| 1. |
- De Campos, Gustavo Bonolo, et al.
(författare)
-
Propulsive efficiency of boundary layer ingestion propellers
- 2018
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Ingår i: 31st Congress of the International Council of the Aeronautical Sciences, ICAS 2018.
-
Konferensbidrag (refereegranskat)abstract
- The pursuit of lower fuel consumption for aircraft is promoting a departure from contemporary arrangements. One example is the development of more synergetic airframe and propulsion system designs, which are expected to increase significantly aircraft efficiency mainly by means of boundary layer ingestion. By integrating propulsion and airframe, both systems will significantly impact each other. This mutual interference requires the development of novel performance evaluation methods that consider such effects. This manuscript introduces a propulsive efficiency equation for boundary layer ingestion propellers based on the power balance method. Two formulations are presented for numerical and analytical evaluations. The equation is bounded between 0 and 1 and allows a meaningful evaluation of shaft to propulsive powers conversion, which results in an accurate determination of thrust and drag. This manuscript is the first advance of a project that will develop an optimizing tool for boundary layer ingestion propellers based on computational fluid dynamic simulations. The results will be presented in subsequent manuscripts.
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| 2. |
- Lundbladh, Anders, 1964, et al.
(författare)
-
Installation effects for ultra-high bypass engines
- 2017
-
Ingår i: International Society of Air-breathing Engines (ISABE).
-
Konferensbidrag (refereegranskat)abstract
- In the pursuit of ever more fuel-efficient engines, the fan diameter and bypass ratio are increasing rapidly. Although it allows the engine to perform more efficiently, it penalizes the aircraft performance with bigger nacelles, meaning more weight and bigger wetted drag-generating area. The nacelle design of such high bypass ratio engine is a problem, as the efficiency gain from the engine is counterbalanced, and sometimes eliminated by the nacelle weight and drag penalty.The paper presents a method that allows for a parametric design of two-dimensional axisymmetric nacelle geometry based on the shape function approach. An automated process is created that generates nacelle designs based on only a few parameters, meshes, and numerically computes the flow around the designed nacelles. A drag bookkeeping system is defined, and the nacelle drag is extracted from the simulation and analysed.The computed drag of nacelles, ranging from conventional length and thickness nacelles, through short/thin nacelles and ultrashort fan shrouds is analysed. Contrary to the first belief, ultrashort nacelles generate more drag than conventional length when the after-body drag-generating surfaces are considered. Furthermore, the study shows that shorter nacelle will greatly increase the flow velocity around the nacelle cowl and create a shock that induces wave drag.A boundary layer ingesting propulsor provides an alternative way to increase propulsive efficiency. The same automated design method was used to generate two differently sized propulsors mounted behind a fuselage, and the flow was numerically computed. In this case the flow around the nacelle cowl was found to be subsonic without shocks. The value of boundary pressure loss and ingested drag was shown to be predictable from the total pressure in the boundary layer on a similar fuselage without propulsor.
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| 3. |
- Petit, Olivier, 1980
(författare)
-
1D System Transients Coupled with 3D Local Flow Details
- 2016
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This work is a numerical study of the water flow in a square channel, during the closure of a gate. The flow is driven by a difference in surface elevation between an upstream and a downstream water tank. The case resembles, for example, the flow in hydro power water ways during a sudden closure of a turbine unit, in which it is of interest to quantify the amplitude and frequency of the following pressure waves.This work is a continuation of the senior SVC project aiming at studying 1D-3D coupling and system transients coupled to local flow unsteadiness. That project presented initial experimental and numerical studies under the same conditions as in the present work. The current objective is to address the numerical modeling of transients with special focus on detailed 3D processes interacting with the flow in an essentially 1D geometry. First the pressure oscillations observed during the easurement campaign when the gate is closed is analyzed. 3D simulations are performed using a computational domain that includes the upper and lower tank and its free surfaces. A flow rate is specified both at the inlet and outlet of the system, and the free surfaces dictates the pressure level in the system. A lot of time was spent dealing with a flow regulation valve below the upper tank that generated a pressure loss in the system, which was unfortunately not taken notice of in the original experimental study. The flow is assumed to be incompressible, and the time dependent Navier Stokes equations are solved in the system. The closing gate is modelled by cutting up the computational mesh. The results show that both the flow and the pressure behave as in the experiment. The pressure levels are similar as those in the experiment, since the loss generated by the regulating valve is taken into account. The oscillations observed in the experiments are not present in the numerical results, and it is suggested that these fluctuations observed in the measurement campaign are indeed pressure transients occurring due to the water hammer effect. Secondly, the upper tank and the pipe are modelled using a compressible 1D code based on the method of characteristics (MOC). A comparison with the experimental data shows that the correct unsteady behavior of the system is captured by the 1D approach if the losses and the gate characteristics are correctly accounted for, at the same time as the compressibility is adapted to the air contents of the water and flexibility of the structure. Finally, a coupled 1D-3D method is introduced, that combines the precision of the three-dimensional modelling in regions where the flow is complicated, and the simplicity and speed of the one-dimensional modelling for the pipe system. The simulations are time-resolved. The results obtained with the 1D-3D coupling method are in very good agreement with the experiments, and show that the method works.
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| 4. |
- Petit, Olivier, 1980, et al.
(författare)
-
A swirl generator case study for OpenFOAM
- 2010
-
Ingår i: 25th IAHR Symposium on Hydraulic Machinery and Systems.
-
Konferensbidrag (refereegranskat)abstract
- This work presents numerical results, using OpenFOAM, of the flow in the swirl flow generator test rig developed at Politehnica University of Timisoara, Romania. The work shows results computed by solving the unsteady Reynolds Averaged Navier Stokes equations. The unsteady method couples the rotating and stationary parts using a sliding grid interface based on a GGI formulation. Turbulence is modeled using the standard k-epsilon model, and block structured wall function ICEM-Hexa meshes are used. The numerical results are validated against experimental LDV results, and against designed velocity profiles. The investigation shows that OpenFOAM gives results that are comparable to the experimental and designed profiles. This case study was presented at the 5th OpenFOAM Workshop, held in Gothenburg, Sweden, as a tutorial on how to treat turbomachinery applications in OpenFOAM.
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| 5. |
- Petit, Olivier, 1980, et al.
(författare)
-
An outlook for radical aero engine intercooler concepts
- 2016
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Ingår i: Proceedings of ASME Turbo Expo 2016: Turbine Technical Conference and Exposition, Seoul, South Korea, Jun 13-17, 2016. - 9780791849743 ; 3
-
Konferensbidrag (refereegranskat)abstract
- A state of the art turbofan engine has an overall efficiency of about 40%, typically composed of a 50% thermal and an 80% propulsive efficiency. Previous studies have estimated that intercooling may improve fuel burn on such an engine with a 3-5% reduction depending on mission length. The intercooled engine benefits stem firstly from a higher Overall Pressure Ratio (OPR) and secondly from a reduced cooling flow need. Both aspects relate to the reduced compressor exit temperature achieved by the intercooler action. A critical aspect of making the intercooler work efficiently is the use of a variable intercooler exhaust nozzle. This allows reducing the heat extracted from the core in cruise operation as well as reducing the irreversibility generated on the intercooler external surface which arises from bypass flow pressure losses. In this respect the improvements, higher OPR and lower cooling flow need, are achieved indirectly and not by directly improving the underlying thermal efficiency. This paper discusses direct methods to further improve the efficiency of intercooled turbofan engines, either by reducing irreversibility generated in the heat exchanger or by using the rejected heat from the intercooler to generate useful power to the aircraft. The performance improvements by using the nacelle wetted surface to replace the conventional intercooler surface is first estimated. The net fuel burn benefit is estimated at 1.6%. As a second option a fuel cooled intercooler configuration, operated during the climb phase, is evaluated providing a net fuel burn reduction of 1.3%. A novel concept that uses the rejected heat to generate additional useful power is then proposed. A secondary cycle able to convert rejected intercooler heat to useful thrust is used to evaluate three possible scenarios. The two first cases investigate the impact of the heat transfer rate on the SFC reduction. As a final consideration the geared intercooled engine cycle is re-optimized to maximize the benefits of the proposed heat recovery system. The maximum SFC improvement for the three cycles is established to 2%, 3.7% and 3%.
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| 6. |
- Petit, Olivier, 1980, et al.
(författare)
-
Comparison of numerical and experimental results of the flow in the U9 Kaplan turbine model
- 2010
-
Ingår i: 25th IAHR Symposium on Hydraulic Machinery and Systems. - London : IOP Publishing Ltd. ; , s. 12024-
-
Konferensbidrag (refereegranskat)abstract
- The present work compares simulations made using the OpenFOAM CFD code with experimental measurements of the flow in the U9 Kaplan turbine model. Comparisons of the velocity profiles in the spiral casing and in the draft tube are presented. The U9 Kaplan turbine prototype located in Porjus and its model, located in Älvkarleby, Sweden, have curved inlet pipes that lead the flow to the spiral casing. Nowadays, this curved pipe and its effect on the flow in the turbine is not taken into account when numerical simulations are performed at design stage. To study the impact of the inlet pipe curvature on the flow in the turbine, and to get a better overview of the flow of the whole system, measurements were made on the 1:3.1 model of the U9 turbine. Previously published measurements were taken at the inlet of the spiral casing and just before the guide vanes, using the laser Doppler anemometry (LDA) technique. In the draft tube, a number of velocity profiles were measured using the LDA techniques. The present work extends the experimental investigation with a horizontal section at the inlet of the draft tube. The experimental results are used to specify the inlet boundary condition for the numerical simulations in the draft tube, and to validate the computational results in both the spiral casing and the draft tube. The numerical simulations were realized using the standard k-e model and a block-structured hexahedral wall function mesh.
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| 7. |
- Petit, Olivier, 1980, et al.
(författare)
-
Numerical and experimental investigations of a hydraulic pipe during a gate closure at high Reynolds number
- 2015
-
Ingår i: 6th IAHR meeting of the Working Group Cavitation and dynamic problems. - : Faculty of technologies and systems.
-
Konferensbidrag (refereegranskat)abstract
- The role of hydropower to provide regulated power is important to the Swedish power system. This becomes even more accentuated with the expansion of intermittent renewable electricity sources, such as wind power. The variation of hydropower operation ranges over a large spectrum of time scales, from seconds to years. For scales larger than a minute, the flow may be considered as quasi-steady from a hydrodynamic point of view. The present work addresses the shorter time scales. Such scales are manifested mainly as pressure transients, which is an issue of concern in design and operation of hydropower plants.The objective of the study is to address rapid pressure transients with a special focus on detailed 3D processes interacting with transients travelling in an essentially 1D geometry. The test case is a gate closing in a long rectangular pipe, where a high-Reynolds number flow is driven by a pressure difference between upper and lower water levels. Experimental time-resolved static pressure and PIV data are gathered for validation of the numerical results.In a first stage the computational domain is modelled in 3D with an incompressible volume of fluid method that includes the prediction of the free surfaces. The domain includes the upper and lower water tanks with free water surfaces, a pipe in-between and a closing and opening gate. The gate movement is modelled with a dynamic mesh that removes the cells as the gate closes. The block-structured mesh is generated in ICEM CFD, and parallel simulations are performed using the OpenFOAM open source software. The numerical results are compared with the experimental data, and it is shown that the experimentally observed pressure fluctuations after gate closure are not an effect of the free surfaces.In a second stage, the upper tank and the pipe are modelled using a compressible 1D code based on the method of characteristics (MOC). A comparison with the experimental data shows that the correct unsteady behavior of the system is captured by the 1D approach if the losses and the gate characteristics are correctly accounted for, at the same time as the compressibility is adapted to the air contents of the water and flexibility of the structure.
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| 8. |
- Petit, Olivier, 1980
(författare)
-
Numerical Investigations of Incompressible Turbomachinery Applications using OpenFOAM
- 2010
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Swirling flow and unsteady phenomena are common in technical applications, such as turbines, pumps and compressors. The objective of this work is to get a good understanding of the turbulent flow features inside such applications, and to validate the computational techniques used for such applications.Because of the complexity of the turbulent flow, approximations are made when solving the flow equations in the computational domain. Depending on the level of the approximations, the level of accuracy and detail in the predicted flow will vary. To validate the assumptions used in the simulations and to get a good prediction of the flow, the computational technique as well as the CFD code must thus be validated against detailed measurements.The present work aims at getting a good understanding of the turbulent flow in the U9 Kaplan turbine model, using the OpenFOAM CFD code. Detailed measurements are used to validate the computed turbulent flow features.
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| 9. |
- Petit, Olivier, 1980, et al.
(författare)
-
Numerical Investigations of Unsteady Flow in a Centrifugal Pump with a Vaned Diffuser
- 2013
-
Ingår i: International Journal of Rotating Machinery. - : Hindawi Limited. - 1542-3034 .- 1023-621X. ; Volume 2013
-
Tidskriftsartikel (refereegranskat)abstract
- Computational fluid dynamics (CFD) analyses were made to study the unsteady three-dimensional turbulence in the ERCOFTACcentrifugal pump test case. The simulations were carried out using the OpenFOAM Open Source CFD software. The test caseconsists of an unshrouded centrifugal impeller with seven blades and a radial vaned diffuser with 12 vanes. A large number ofmeasurements are available in the radial gap between the impeller and the diffuse, making this case ideal for validating numericalmethods. Results of steady and unsteady calculations of the flow in the pump are compared with the experimental ones, and fourdifferent turbulent models are analyzed. The steady simulation uses the frozen rotor concept, while the unsteady simulation uses afully resolved sliding grid approach. The comparisons show that the unsteady numerical results accurately predict the unsteadinessof the flow, demonstrating the validity and applicability of that methodology for unsteady incompressible turbomachinery flowcomputations.The steady approach is less accurate, with an unphysical advection of the impeller wakes, but accurate enough for acrude approximation. The different turbulence models predict the flow at the same level of accuracy, with slightly different results.
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| 10. |
- Petit, Olivier, 1980, et al.
(författare)
-
The ERCOFTAC centrifugal pump OpenFOAM case-study
- 2009
-
Ingår i: IAHR International Meeting of the Workgroup on Cavitation and Dynamic Problems in Hydraulic Machinery and Systems. - 9788021439474 ; , s. 523-532
-
Konferensbidrag (refereegranskat)abstract
- This work investigates the rotor-stator interaction features of OpenFOAM-1.5-dev, such as frozenrotor and sliding grid. The case studied is the ERCOFTAC Test Case U3: Centrifugal Pump with aVaned Diffuser, a testcase from the ERCOFTAC Turbomachinery Special Interest Group. The casewas presented by Combès at the ERCOFTAC Seminar and Workshop on Turbomachinery FlowPrediction VII, in Aussois, 1999. It is a valid test case for evaluation of rotor-stator interactionfeatures, as detailed experimental data is available.The investigation shows that OpenFOAM gives results that are comparable to the experimental data,in particular for the sliding grid case. The results are less accurate in the frozen rotor simulation due tothe improper treatment of the impeller wakes that is part of the frozen rotor formulation.The ERCOFTAC centrifugal pump OpenFOAM case-study was developed as a contribution to theOpenFOAM Turbomachinery Working Group, and was presented and discussed at the FourthOpenFOAM Workshop in Montréal, 2009. The complete set-up of the case-study is available from theOpenFOAM-extend project at SourceForge, and instructions and comments are available from theOpenFOAM Wiki.
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| 11. |
- Petit, Olivier, 1980, et al.
(författare)
-
The flow in the U9 Kaplan turbine - preliminary and planned simulations using CFX and OpenFOAM
- 2008
-
Ingår i: 24th IAHR Symposium Hydraulic MAchinery and Systems, Foz Do Iguassu, Brasil.
-
Konferensbidrag (refereegranskat)abstract
- The present work compares the CFX and OpenFOAM CFD codes with respect to the prediction of the flow in the U9 Kaplan turbine spiral casing, distributor and draft tube. The simulations use similar settings and the same computational grids – unstructured wall-function grids with 10.3M cells in the spiral casing and distributor, and 1.04M cells in the draft tube. The results show that the two codes give similar results in the spiral casing and distributor, and almost identical results in the draft tube. Previous studies [1] have shown the same behaviour in the Turbine-99 draft tube, for a block-structured wall-function grid. There are however no previous studies where the flow in a spiral casing and distributor have been studied and compared using the same settings and computational grid in CFX and OpenFOAM.The next phase of the project consists of comparisons with the results from an on-going experimental investigation.
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| 12. |
- Petit, Olivier, 1980
(författare)
-
Towards Full Predictions of the Unsteady Incompressible Flow in Rotating Machines, Using OpenFOAM
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main objective of the present work is to validatemethodologies for accurate numerical predictions of the incompressible flow ofwater in the U9 Kaplan turbine model. The term “prediction” implies that the useof detailed experimental data for boundary conditions should be avoided, andthat all important features of the studied case should be included. Thatincludes specifying boundary conditions at locations where the flow conditionscan be easily estimated, and where reasonable variations in those estimations donot significantly affect the flow prediction. As an example, the U9 Kaplanturbine model has a sharply bent inlet pipe, and it is here argued that thesecondary flow from that should be taken into account by including the pipe inthe simulation. In the case of rotating machines, such as the U9 Kaplan turbinemodel, the interaction between rotating and stationary components (rotor-statorinteraction) is a feature that must be included in the simulations.Three highly relevant well-documented cases have been used in the present work,the ERCOFTAC Centrifugal Pump, the Timisoara Swirl Generator and the U9 Kaplanturbine model. All three cases include rotor-stator interaction. The latter,being the main goal of the studies, has just recently been studiedexperimentally and is a computationally demanding case. Thus, the former twocases were used while validating the new implementations and evaluating thenumerical settings, until the results were reliable and efficient. Two rotor-statorinteraction methods were investigated, the steady-state frozen-rotor approach,and the unsteady sliding grid approach, and the results from four turbulencemodels were compared.The results show that both approaches canbe used to couple the rotating and stationary parts of the domain. However, thefrozen rotor yields an unphysical advection of the runner wakes, and suchresults should only be used for a first estimation or as initial conditions forfull unsteady sliding grid simulations. The predictions compare very well withthe experimental results, and the main differences can be explained by thegeometrical simplifications that were made. The four turbulence models behavesimilarly, with a minor preference for different models in the different cases.The present work is done using the OpenFOAM OpenSource CFD toolbox. The code ischosen to facilitate an OpenSource distribution of the developments, to beshared in the scientific community, and to be directly useful in industry. It was not possible to achieve the results presented here with OpenFOAM before the start of the present work,which has significantly contributed to the validation of, and trust in, the newimplementations.
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| 13. |
- Petit, Olivier, 1980, et al.
(författare)
-
Unsteady Simulations of the Flow in a Swirl Generator, using OpenFOAM
- 2011
-
Ingår i: International Journal of Fluid Machinery and Systems. - 1882-9554. ; 4:1, s. pp.199-208
-
Tidskriftsartikel (refereegranskat)abstract
- This work presents numerical results, using OpenFOAM, of the flow in the swirl flow generator test rig developed at Politehnica University of Timisoara, Romania. The work shows results computed by solving the unsteady Reynolds Averaged Navier Stokes equations. The unsteady method couples the rotating and stationary parts using a sliding grid interface based on a GGI formulation. Turbulence is modeled using the standard k-ε model, and block structured wall function ICEM-Hexa meshes are used. The numerical results are validated against experimental LDV results, and against design velocity profiles. The investigation shows that OpenFOAM gives results that are comparable to the experimental and design profiles. The unsteady pressure fluctuations at four different positions in the draft tube is recorded. A Fourier analysis of the numerical results is compared whit that of the experimental values. The amplitude and frequency predicted by the numerical simulation are comparable to those given by the experimental results, though slightly over estimated.
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| 14. |
- Samuelsson, Sebastian, 1987, et al.
(författare)
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Adaption of a Turbofan Engine for High Power Offtakes for a Turbo-electric Propulsive Fuselage Concept
- 2019
-
Ingår i: ISABE 2019 Papers.
-
Konferensbidrag (refereegranskat)abstract
- To lower the fuel consumption and its associated emissions, several new aircraft concepts are being investigated. One such concept is the turbo-electric propulsive fuselage concept (PFC) that is being studied in the EU Horizon 2020 project CENTRELINE for a 2035 entry into service (EIS). The PFC makes use of a rear-mounted electric fuselage fan to ingest part of the fuselage boundary layer. The fuselage fan is powered by power offtakes from two under-wing podded geared turbofans. In this paper, a design of the under-wing main power plants is presented and compared to an engine for a conventional reference aircraft with the same EIS year. A free power turbine (PT) stage for the large power offtake required is added aft of the low pressure turbine (LPT). The PT is connected to an electric generator on the same shaft that is integrated in the PT hub. The addition of the PT allows for mechanically decoupling the electric machinery from the LP spool, which is considered beneficial for the electric machinery operation. It also allows for a removal of one LPT stage compared to the reference engine. The power plants for the PFC show a reduction of fan diameter by 11%, as well as a reduction in engine weight of 13% excluding the electric machinery weight.
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| 15. |
- Seitz, Arne, et al.
(författare)
-
Concept validation study for fuselage wake-filling propulsion integration
- 2018
-
Ingår i: 31st Congress of the International Council of the Aeronautical Sciences, ICAS 2018.
-
Konferensbidrag (refereegranskat)abstract
- The present paper provides an overview together with intermediate results of the work-in-progress research performed in the EC-funded Horizon 2020 collaborative project CENTRELINE (“ConcEpt validatioN sTudy foR fusElage wake-filLIng propulsioN integration”), aiming at demonstrating the proof of concept for a groundbreaking approach to synergistic propulsion-airframe integration, the so-called Propulsive Fuselage Concept (PFC). The concept features a turbo-electrically driven propulsive device integrated in the very aft-section of the fuselage, dedicated to the purpose of fuselage wake-filling. Currently at TRL 1-2, CENTRELINE's target is to mature the technological key features of the PFC to TRL 3-4. The core of the targeted proof-of-concept is formed by two experimental test campaigns supported by high-fidelity 3D numerical simulation and integrated multidisciplinary design optimisation techniques for aerodynamics, aero-structures as well as the energy and propulsion system.
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| 16. |
- Silva, Vinicius Tavares, et al.
(författare)
-
Numerical Simulation of Nacelle Flowfield for Counter-Rotating Open Rotor Propellers
- 2017
-
Ingår i: International Society of Air-breathing Engines (ISABE).
-
Konferensbidrag (refereegranskat)abstract
- This paper summarizes the development of a tool for designing axisymmetric nacelles for counter-rotating open rotor (CROR) engines, based on predefined geometries, global input relations and one-dimensional perfect gas equations. A nacelle geometry was generated to match the flight conditions and base dimensions of the Airbus AI-PX7 CROR propeller. Furthermore, the 3D turbulent flowfield around the nacelle was evaluated via Computational Fluid Dynamics (CFD) for four different angles of attack: 0°, 4°, 6° and 8°. The computations were performed for the nacelle without the propellers as a first analysis. The formation of shock waves, boundary layer separation and inlet flow distortion were the main parameters of the CFD study. The nacelle design was considered to be successful as a preliminary approach, since, even for the highest angle of attack, no critical conditions for the engine performance were detected.
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| 17. |
- Tavares Silva, Vinícius, 1991, et al.
(författare)
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Influence of Variable Geometry Compressor on Transient Performance of Counter-Rotating Open Rotor Engines
- 2018
-
Ingår i: Journal of Engineering for Gas Turbines and Power. - : ASME International. - 1528-8919 .- 0742-4795. ; 140:12
-
Tidskriftsartikel (refereegranskat)abstract
- This work describes a methodology used for counter-rotating (CR) propellers performance estimation. The method is implemented in an in-house program for gas turbine performance prediction, making possible the simulation of the counter-rotating open rotor (CROR) architecture. The methodology is used together with a variable geometry compressor control strategy to avoid surge conditions. Two cases are simulated under transient operation for both fixed and variable geometry compressor. The influence of the variable geometry control on the transient performance of CROR engines is evaluated and a comprehensive understanding on the transient behavior of this type of engine could be obtained. It is shown that the use of the variable geometry compressor control does not significantly affect the overall engine performance, while avoiding the surge conditions, thus ensuring the engine operation safety.
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| 18. |
- Tavares Silva, Vinícius, 1991, et al.
(författare)
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Multipoint aerodynamic design of ultrashort nacelles for ultrahigh-bypass-ratio engines
- 2022
-
Ingår i: Journal of Propulsion and Power. - 1533-3876 .- 0748-4658. ; 38:4, s. 541-558
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a newly developed methodology for multipoint aerodynamic design of ultrashort nacelles for ultrahigh-bypass-ratio turbofan engines. An integrated aerodynamic framework, based on parametric geometry generation and flowfield solution via three-dimensional Reynolds-averaged Navier-Stokes equations, was built and used for designing several ultrashort nacelle shapes and to evaluate their aerodynamic performance. An approach for modeling the inlet-fan coupling is presented and validated. A design strategy is introduced, and various test cases are evaluated under the following critical operating conditions: midcruise, low speed/high angle of attack, and pure crosswind. The major design parameters are highlighted and their influence in the flowfield is discussed in detail for all the chosen flight conditions. Performance was evaluated by assessing inlet flow distortion and by bookkeeping of thrust and drag. The framework has proven to be suitable for designing high-performance nacelles capable of operating under critical flight conditions, without flow separation or high levels of distortion. Drooping the inlet by 4 deg is shown to reduce the drag at cruise by 1.9%, which also has a large beneficial impact on internal lip separation at high-incidence conditions. Furthermore, crosswind was identified as the most severe of the conditions, requiring a drastic reshaping of the nacelle to avoid internal lip separation. Two final nacelle designs were compared: the first allowed inlet separation under a 90 deg crosswind condition, whereas the second was reshaped to be separation-free under all operating conditions. Reshaping to avoid separation has increased drag by 5.1% at cruise.
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| 19. |
- Thulin, Oskar, 1987, et al.
(författare)
-
First and second law analysis of radical intercooling concepts
- 2017
-
Ingår i: Proceedings of the ASME Turbo Expo. - 9780791850770 ; 1
-
Konferensbidrag (refereegranskat)abstract
- An exergy framework was developed taking into consideration a detailed analysis of the heat exchanger (intercooler) component irreversibilities. Moreover, it was further extended to include an adequate formulation for closed systems, e.g. a secondary cycle, moving with the aircraft. Afterwards the proposed framework was employed to study two radical intercooling concepts. The first proposed concept uses already available wetted surfaces, i.e. nacelle surfaces, to reject the core heat and contribute to an overall drag reduction. The second concept uses the rejected core heat to power a secondary organic Rankine cycle and produces useful power to the aircraft-engine system. Both radical concepts are integrated into a high bypass ratio turbofan engine, with technology levels assumed to be available by year 2025. A reference intercooled cycle incorporating a heat exchanger in the bypass duct is established for comparison. Results indicate that the radical intercooling concepts studied in this paper show similar performance levels to the reference cycle. This is mainly due to higher irreversibility rates created during the heat exchange process. A detailed assessment of the irreversibility contributors, including the considered heat exchangers and the secondary cycle major components is made. A striking strength of the present analysis is the assessment of the component irreversibility rate and its contribution to the overall aero-engine losses.
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| 20. |
- Thulin, Oskar, 1987, et al.
(författare)
-
First and Second Law Analysis of Radical Intercooling Concepts
- 2018
-
Ingår i: Journal of Engineering for Gas Turbines and Power. - : ASME International. - 1528-8919 .- 0742-4795. ; 140:8, s. 081201-081201-10
-
Tidskriftsartikel (refereegranskat)abstract
- An exergy framework was developed taking into consideration a detailed analysis of the heat exchanger (HEX) (intercooler (IC)) component irreversibilities. Moreover, it was further extended to include an adequate formulation for closed systems, e.g., a secondary cycle (SC), moving with the aircraft. Afterward, the proposed framework was employed to study two radical intercooling concepts. The first proposed concept uses already available wetted surfaces, i.e., nacelle surfaces, to reject the core heat and contributes to an overall drag reduction. The second concept uses the rejected core heat to power a secondary organic Rankine cycle and produces useful power to the aircraft-engine system. Both radical concepts are integrated into a high bypass ratio (BPR) turbofan engine, with technology levels assumed to be available by year 2025. A reference intercooled cycle incorporating a HEX in the bypass (BP) duct is established for comparison. Results indicate that the radical intercooling concepts studied in this paper show similar performance levels to the reference cycle. This is mainly due to higher irreversibility rates created during the heat exchange process. A detailed assessment of the irreversibility contributors, including the considered HEXs and SC, is made. A striking strength of the present analysis is the assessment of the component-level irreversibility rate and its contribution to the overall aero-engine losses.
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| 21. |
- Wang, Chao, et al.
(författare)
-
1D-3D coupling for hydraulic system transient simulations
- 2017
-
Ingår i: Computer Physics Communications. - : Elsevier BV. - 0010-4655. ; 210, s. 1-9
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Tidskriftsartikel (refereegranskat)abstract
- This work describes a coupling between the 1D method of characteristics (MOC) and the 3D finite volume method of computational fluid dynamics (CFD). The coupling method is applied to compressible flow in hydraulic systems. The MOC code is implemented as a set of boundary conditions in the OpenFOAM open source CFD software. The coupling is realized by two linear equations originating from the characteristics equation and the Riemann constant equation, respectively. The coupling method is validated using three simple water hammer cases and several coupling configurations. The accuracy and robustness are investigated with respect to the mesh size ratio across the interface and to 3D flow features close to the interface. The method is finally applied to the transient flow caused by the closing and opening of a knife valve (gate) in a pipe, where the flow is driven by the difference in free surface elevation between two tanks. A small region surrounding the moving gate is resolved by CFD, using a dynamic mesh library, while the rest of the system is modeled by MOC. Minor losses are included in the 1D region, corresponding to the contraction of the flow from the upstream tank into the pipe, a separate stationary flow regulation valve, and a pipe bend. The results are validated with experimental data. A 1D solution is provided for comparison, using the static gate characteristics obtained from steady-state CFD simulations.
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| 22. |
- Xisto, Carlos, 1984, et al.
(författare)
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Analytical model for the performance estimation of pre-cooled pulse detonation turbofan engines
- 2017
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Ingår i: Proceedings of the ASME Turbo Expo. ; 1
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Konferensbidrag (refereegranskat)abstract
- This paper proposes a pulse detonation combustion (PDC) model integrated within Chalmers University' s gas turbine simulation tool GESTPA N (GEneral Stationary and Transient Propulsion ANalsysis). The model will support the development of novel aircraft engine architectures exploiting the synergies between intercooling, aftercooling and PDC. The proposed engine architectures are based on a reference high bypass ratio geared-turbofan engine model with performance levels estimated to be available by year 2050. Parametric studies have been carried out for each proposed advanced architecture, providing engine cycle mid-cruise design point parameters. Design sensitivity studies related to intercooling technology in combination with a PDC are further explored for a number of heat-exchanger design effectiveness values and associated pressure loss levels. The acquired results suggest that the incorporation of PDC technology within a conventional core has the potential to significantly improve engine thermal efficiency. Incorporating intercooling improves the cycle performance for any pre-combustion OPR above 10 and contributes to an increase in specific power over the entire range of OPR. Finally, the results demonstrate that aftercooling the high pressure compressor delivery air further improves core specific power, but cancels out any SFC and thermal efficiency benefits arising from pulse detonation.
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| 23. |
- Xisto, Carlos, 1984, et al.
(författare)
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Assessment of CO2 and NOx emissions in intercooled pulsed detonation turbofan engines
- 2018
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Ingår i: Proceedings of the ASME Turbo Expo. ; 1
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Konferensbidrag (refereegranskat)abstract
- In the present paper, the synergistic combination of intercooling with pulsed detonation combustion is analyzed concerning its contribution to NOxand CO2emissions. CO2is directly proportional to fuel burn and can, therefore, be reduced by improving specific fuel consumption and reducing engine weight and nacelle drag. A model predicting NOxgeneration per unit of fuel for pulsed detonation combustors, operating with jet-A fuel, is developed and integrated within Chalmers University's gas turbine simulation tool GESTPAN. The model is constructed using CFD data obtained for different combustor inlet pressure, temperature and equivalence ratio levels. The NOxmodel supports the quantification of the trade-off between CO2and NOxemissions in a 2050 geared turbofan architecture incorporating intercooling and pulsed detonation combustion and operating at pressures and temperatures of interest in gas turbine technology for aero-engine civil applications.
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| 24. |
- Xisto, Carlos, 1984, et al.
(författare)
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Assessment of CO2 and NOx emissions in intercooled pulsed detonation turbofan engines
- 2019
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Ingår i: Journal of Engineering for Gas Turbines and Power. - : ASME International. - 1528-8919 .- 0742-4795. ; 141:1
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Tidskriftsartikel (refereegranskat)abstract
- In the present paper, the synergistic combination of intercooling with pulsed detonation combustion is analyzed concerning its contribution to NOx and CO2 emissions. CO2 is directly proportional to fuel burn and can, therefore, be reduced by improving specific fuel consumption and reducing engine weight and nacelle drag. A model predicting NOx generation per unit of fuel for pulsed detonation combustors, operating with jet-A fuel, is developed and integrated within Chalmers University's gas turbine simulation tool GESTPAN. The model is constructed using CFD data obtained for different combustor inlet pressure, temperature and equivalence ratio levels. The NOx model supports the quantification of the trade-off between CO2 and NOx emissions in a 2050 geared turbofan architecture incorporating intercooling and pulsed detonation combustion and operating at pressures and temperatures of interest in gas turbine technology for aero-engine civil applications.
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| 25. |
- Xisto, Carlos, 1984, et al.
(författare)
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The Efficiency of a Pulsed Detonation Combustor-Axial Turbine Integration
- 2018
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Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638. ; 82-83, s. 80-91
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Tidskriftsartikel (refereegranskat)abstract
- The paper presents a detailed numerical investigation of a pulsed detonation combustor (PDC) coupled with a transonic axial turbine stage. The time-resolved numerical analysis includes detailed chemistry to replicate detonation combustion in a stoichiometric hydrogen–air mixture, and it is fully coupled with the turbine stage flow simulation. The PDC–turbine performance and flow variations are analyzed for different power input conditions, by varying the system purge fraction. Such analysis allows for the establishment of cycle averaged performance data and also to identify key unsteady gas dynamic interactions occurring in the system. The results obtained allow for a better insight on the source and effect of different loss mechanisms occurring in the coupled PDC–turbine system. One key aspect arises from the interaction between the non-stationary PDC outflow and the constant rotor blade speed. Such interaction results in pronounced variations of rotor incidence angle, penalizing the turbine efficiency and capability of generating a quasi-steady shaft torque.
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