| 131. |
- Saha, Ranjan, 1984-
(författare)
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Aerodynamic Investigation of Leading Edge Contouring and External Cooling on a Transonic Turbine Vane
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Efficiency improvement in turbomachines is an important aspect in reducing the use of fossil-based fuel and thereby reducing carbon dioxide emissions in order to achieve a sustainable future. Gas turbines are mainly fossil-based turbomachines powering aviation and land-based power plants. In line with the present situation and the vision for the future, gas turbine engines will retain their central importance in coming decades. Though the world has made significant advancements in gas turbine technology development over past few decades, there are yet many design features remaining unexplored or worth further improvement. These features might have a great potential to increase efficiency. The high pressure turbine (HPT) stage is one of the most important elements of the engine where the increased efficiency has a significant influence on the overall efficiency as downstream losses are substantially affected by the prehistory. The overall objective of the thesis is to contribute to the development of gas turbine efficiency improvements in relation to the HPT stage. Hence, this study has been incorporated into a research project that investigates leading edge contouring near endwall by fillet and external cooling on a nozzle guide vane with a common goal to contribute to the development of the HPT stage. In the search for HPT stage efficiency gains, leading edge contouring near the endwall is one of the methods found in the published literature that showed a potential to increase the efficiency by decreasing the amount of secondary losses. However, more attention is necessary regarding the realistic use of the leading edge fillet. On the other hand, external cooling has a significant influence on the HPT stage efficiency and more attention is needed regarding the aerodynamic implication of the external cooling. Therefore, the aerodynamic influence of a leading edge fillet and external cooling, here film cooling at profile and endwall as well as TE cooling, on losses and flow field have been investigated in the present work. The keystone of this research project has been an experimental investigation of a modern nozzle guide vane using a transonic annular sector cascade. Detailed investigations of the annular sector cascade have been presented using a geometric replica of a three dimensional gas turbine nozzle guide vane. Results from this investigation have led to a number of new important findings and also confirmed some conclusions established in previous investigations to enhance the understanding of complex turbine flows and associated losses. The experimental investigations of the leading edge contouring by fillet indicate a unique outcome which is that the leading edge fillet has no significant effect on the flow and secondary losses of the investigated nozzle guide vane. The reason why the leading edge fillet does not affect the losses is due to the use of a three-dimensional vane with an existing typical fillet over the full hub and tip profile. Findings also reveal that the complex secondary flow depends heavily on the incoming boundary layer. The investigation of the external cooling indicates that a coolant discharge leads to an increase of profile losses compared to the uncooled case. Discharges on the profile suction side and through the trailing edge slot are most prone to the increase in profile losses. Results also reveal that individual film cooling rows have a weak mutual effect. A superposition principle of these influences is followed in the midspan region. An important finding is that the discharge through the trailing edge leads to an increase in the exit flow angle in line with an increase of losses and a mixture mass flow. Results also indicate that secondary losses can be reduced by the influence of the coolant discharge. In general, the exit flow angle increases considerably in the secondary flow zone compared to the midspan zone in all cases. Regarding the cooling influence, the distinct change in exit flow angle in the area of secondary flows is not noticeable at any cooling configuration compared to the uncooled case. This interesting zone requires an additional, accurate study. The investigation of a cooled vane, using a tracer gas carbon dioxide (CO2), reveals that the upstream platform film coolant is concentrated along the suction surfaces and does not reach the pressure side of the hub surface, leaving it less protected from the hot gas. This indicates a strong interaction of the secondary flow and cooling showing that the influence of the secondary flow cannot be easily influenced. The overall outcome enhances the understanding of complex turbine flows, loss behaviour of cooled blade, secondary flow and interaction of cooling and secondary flow and provides recommendations to the turbine designers regarding the leading edge contouring and external cooling. Additionally, this study has provided to a number of new significant results and a vast amount of data, especially on profile and secondary losses and exit flow angles, which are believed to be helpful for the gas turbine community and for the validation of analytical and numerical calculations.
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| 132. |
- Saha, Ranjan, 1984-, et al.
(författare)
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Influence of Prehistory and Leading Edge Contouring on Aero Performance of a Three-Dimensional Nozzle Guide Vane
- 2014
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Ingår i: Journal of turbomachinery. - : ASME Press. - 0889-504X .- 1528-8900. ; 136:7, s. 071014-1-071014-10
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Tidskriftsartikel (refereegranskat)abstract
- Experiments are conducted to investigate the effect of the prehistory in the aerodynamic performance of a three-dimensional nozzle guide vane with a hub leading edge contouring. The performance is determined with two pneumatic probes (five hole and three hole) concentrating mainly on the end wall. The investigated vane is a geometrically similar gas turbine vane for the first stage with a reference exit Mach number of 0.9. Results are compared for the baseline and filleted cases for a wide range of operating exit Mach numbers from 0.5 to 0.9. The presented data includes loading distributions, loss distributions, fields of exit flow angles, velocity vector, and vorticity contour, as well as mass-averaged loss coefficients. The results show an insignificant influence of the leading edge fillet on the performance of the vane. However, the prehistory (inlet condition) affects significantly in the secondary loss. Additionally, an oil visualization technique yields information about the streamlines on the solid vane surface, which allows identifying the locations of secondary flow vortices, stagnation line, and saddle point.
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| 133. |
- Saha, Ranjan, 1984-, et al.
(författare)
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Shower Head and Trailing Edge Cooling Influence on Transonic Vane Aero Performance
- 2014
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Ingår i: ASME Turbo Expo 2014. - : ASME Press. - 9780791845622
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Konferensbidrag (refereegranskat)abstract
- An experimental investigation on a cooled nozzle guide vane has been conducted in an annular sector to quantify aerodynamic influences of shower head and trailing edge cooling. The investigated vane is a typical high pressure gas turbine vane, geometrically similar to a real engine component, operated at a reference exit Mach number of 0.89. The investigations have been performed for various coolant-to-mainstream mass-flux ratios. New loss equations are derived and implemented regarding coolant aerodynamic losses. Results lead to a conclusion that both trailing edge cooling and shower head film cooling increase the aerodynamic loss compared to an uncooled case. In addition, the trailing edge cooling has higher aerodynamic loss compared to the shower head cooling. Secondary losses decrease with inserting shower head film cooling compared to the uncooled case. The trailing edge cooling appears to have less impact on the secondary loss compared to the shower head cooling. Area-averaged exit flow angles around midspan increase for the trailing edge cooling.
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| 134. |
- Saha, Ranjan, 1984-, et al.
(författare)
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Shower Head and Trailing Edge Cooling Influence on Transonic Vane Aero Performance
- 2014
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Ingår i: Journal of turbomachinery. - : ASME Press. - 0889-504X .- 1528-8900. ; 136:11, s. 111001-
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Tidskriftsartikel (refereegranskat)abstract
- An experimental investigation on a cooled nozzle guide vane (NGV) has been conducted in an annular sector to quantify aerodynamic influences of shower head (SH) and trailing edge (TE) cooling. The investigated vane is a typical high pressure gas turbine vane, geometrically similar to a real engine component, operated at a reference exit Mach number of 0.89. The investigations have been performed for various coolant-to-mainstream mass-flux ratios. New loss equations are derived and implemented regarding coolant aerodynamic losses. Results lead to a conclusion that both TE cooling and SH film cooling increase the aerodynamic loss compared to an uncooled case. In addition, the TE cooling has higher aerodynamic loss compared to the SH cooling. Secondary losses decrease with inserting SH film cooling compared to the uncooled case. The TE cooling appears to have less impact on the secondary loss compared to the SH cooling. Area-averaged exit flow angles around midspan increase for the TE cooling.
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| 135. |
- Weng, Zebin, et al.
(författare)
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Performance improvement of variable-angle annular thermoelectric generators considering different boundary conditions
- 2022
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Ingår i: Applied Energy. - : Elsevier BV. - 1872-9118 .- 0306-2619. ; 306
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Tidskriftsartikel (refereegranskat)abstract
- Practical applications of thermoelectric generators are impeded by their low thermoelectric conversion efficiency, and improving the efficiency is vital for the advancements of thermoelectric technology. In this paper, a novel method is proposed for the performance analysis and improvement of the annular thermoelectric generators with variable-angle PN legs (VATEGs). The influence of the PN leg angle on the output performance of the VATEG is investigated by introducing an angle function. Given the volume of the PN legs, the relationship of output performance between the VATEG and traditional constant-angle ATEG (CATEG) is established under different boundary conditions based on a proposed generic model of VATEG. The results are verified numerically using the finite element method. Using the model, it is shown that the output performance of the VATEG is significantly affected by the shape of the PN leg. Finally, the thermal stress on the PN leg is next investigated using a high-fidelity 3D model of the variable-angle PN legs implemented in COMSOL, and it is found that the shape difference has a considerable influence on the thermal stability of VATEG. Under the condition of constant heat flux on the hot side and constant temperature on the cold side of the thermoelectric modules, it shows that when the radius factor is 2, the output performance can be improved by 35% with the designed VATEG, at the expense of 30% higher maximum thermal stress on the PN legs.
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| 136. |
- Abdalla, Alvaro, et al.
(författare)
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The Effect of Engine Dimensions on Supersonic Aircraft Performance
- 2013
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Ingår i: 4:th CEAS Air & Space Conference.
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Konferensbidrag (refereegranskat)abstract
- In aircraft design a critical part of the design isthe engine selection. This is typically making aselection from exiting engines. Looking at a nextgeneration future fighters, however, where thetime of deployment may be 20-30 years in thefuture this is not a valid approach as there willbe an evolution in the engine designs. E.g. anew European fighter aircraft will most likelybe a collaborative project also involving thedevelopment of an engine for that aircraft. Inthis study conceptual engine-airframe co-designis demonstrated, using models of comparablefidelity for both the engine design and theaircraft design. This co-design leads to a deeperunderstanding of the tradeoffs from both sides,and means that also more radical designs andinnovations can be evaluated in a fair way.
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| 137. |
- Alexandersson, Martin, et al.
(författare)
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Prediction of roll motion using fully nonlinear potential flow and ikeda’s method
- 2021
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Ingår i: Proceedings of the International Offshore and Polar Engineering Conference. - : International Society of Offshore and Polar Engineers. - 1098-6189 .- 1555-1792. - 9781880653821 ; , s. 1670-1679
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Konferensbidrag (refereegranskat)abstract
- Getting the best possible accuracy with the lowest possible computational cost is an important factor in the early design stage of ships. Potential flow-based analysis presents such a solution for seakeeping analyses. The accuracy of roll motion in potential flow is however not so good, due to the large influence from vicsous roll damping, which is missing in these calculations. This paper proposes a hybrid method, as a solution to this problem, where the viscous roll damping from Ikeda’s semi-empirical method is injected into an existing 3D unsteady fully nonlinear potential flow (FNPF) method. The hybrid method is investigated using roll decay tests with the KVLCC2 test case. This investigation shows that the accuracy of simulated roll motions is significantly improved and also shows good agreement with the corresponding roll decay model tests.
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| 138. |
- Ask, Jonas, 1970, et al.
(författare)
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Flow and dipole source evaluation of a generic SUV
- 2007
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Ingår i: 13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference). - Reston, Virigina : American Institute of Aeronautics and Astronautics.
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Konferensbidrag (refereegranskat)abstract
- Accurately predicting both average flow quantities and acoustic sources at the front side window of today's ground vehicles is still a considerable challenge to automotive companies world-wide. One of the most important aspects for obtaining trustworthy results, but also the most tedious one and therefore perhaps overlooked, is the control and outcome of the mesh generation process. Generating unstructured volume meshes suitable for Large Eddy Simulations with high level representation of geometrical details is both a time consuming and an extremely computer demanding activity. This work investigates two different mesh generation processes with the main aim to evaluate their outcome with respect to the prediction of the two dominating dipole sources in a temporal form of the Curie's equation. Only a handful of papers exists with high level representation of the vehicle geometry and the aim of predicting the fluctuating exterior noise sources. To the author's knowledge no studies have been conducted in which both these source terms are evaluated quantitatively against measurements. The current paper investigates the degree to which the amplitude of these two source terms can be predicted by using the traditional law-of-the-wall and hex-dominant meshes with isotropic resolution boxes for a detailed ground vehicle geometry. For this purpose the unstructured segregated commercial FLUENT Finite Volume Method code is used. The flow field is treated as incompressible, and the Smagorinsky-Lilly model is used to compute the sub-grid stresses. Mean flow quantities are measured with a 14-hole probe for 14 rakes downstream of the side mirror. Dynamic pressure sensors are distributed at 16 different positions over the side window to capture the fluctuating pressure signals. All measurements in this work were conducted at Ford's acoustic wind tunnel in Cologne. All simulations accurately predict the velocity magnitude closest to the side window and downstream of the mirror head recirculation zoner. Some variations in the size and shape of this recirculation zone are found between the different meshes, most probably caused by differences in the detachment of the mirror head boundary layer. The Strouhal number of the shortest simulation was computed from the fundamental frequency of the mirror lift force component. The computed Strouhal number agrees well with the corresponding results from similar objects and gives an indication of an acceptable simulation time. Dynamic pressure sensors at 16 different locations at the vehicle side window were also used to capture the levels of the two dipole source terms. These results are compared against the three simulations. With the exception of three positions, at least one of the three simulations accurately captures the levels of both source terms up to about 1000Hz. The three positions with less agreement as compared to measurements were found to be in regions sensitive to small changes in the local flow direction.
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| 139. |
- Asnaghi, Abolfazl, 1984, et al.
(författare)
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Propeller tip vortex mitigation by roughness application
- 2021
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Ingår i: Applied Ocean Research. - : Elsevier BV. - 0141-1187. ; 106
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the application of surface roughness on model and full scale marine propellers in order to mitigate tip vortex cavitation is evaluated. To model the turbulence, SST k−ω model along with a curvature correction is employed to simulate the flow on an appropriate grid resolution for tip vortex propagation, at least 32 cells per vortex diameter according to our previous guidelines. The effect of roughness is modelled by modified wall functions. The analysis focuses on two types of vortices appearing on marine propellers: tip vortices developing in lower advance ratio numbers and leading edge tip vortices developing in higher advance ratio numbers. It is shown that as the origin and formation of these two types of vortices differ, different roughness patterns are needed to mitigate them with respect to performance degradation of propeller performance. Our findings clarify that the combination of having roughness on the blade tip and a limited area on the leading edge is the optimum roughness pattern where a reasonable balance between tip vortex cavitation mitigation and performance degradation can be achieved. This pattern in model scale condition leads to an average TVC mitigation of 37% with an average performance degradation of 1.8% while in full scale condition an average TVC mitigation of 22% and performance degradation of 1.4% are obtained.
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| 140. |
- Capitao Patrao, Alexandre, 1988
(författare)
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Simulation and Analysis of a Novel Open Rotor Propeller - the Boxprop
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Economic factors and environmental awareness is driving the evolution of aircraft engines towards increasingly higher efficiencies, reaching for lower fuel consumption and lower emissions. The Counter-Rotating Open Rotor (CROR) is actively being researched around the world, promising a significantly increased propulsion efficiency relative to existing turbofans by employing two, counter-rotating propeller blade rows, thereby increasing the bypass ratio of the engine. Historically, these engines have been plagued by very high noise levels, mainly due to the impingement of the front rotor tip vortices on the rear rotor. In modern designs, the noise levels have been significantly decreased by clipping the rear, counter-rotating propeller. Unfortunately, this comes at a cost of decreased efficiency.An alternative, potential solution lies with the Boxprop, which was invented by Richard Avellán and Anders Lundbladh. The Boxprop consist of blade pairs joined at the tip, and are conceptually similar to box wings. It is hypothesized that the Boxprop can eliminate the tip vortex found in conventional blades, consequently increasing the efficiency of the blades, and reducing their acoustic signature.The present work highlights advances done in the research surrounding the Boxprop. A validation of the deployed CFD methodology is presented, in which numerical and experimental results compare favourably. Performance results for a Boxprop (GP-X-701) designed for cruise conditions are presented and compared with a generic conventional propeller (GP-S-609). It is shown that the present Boxprop cruise design can reach the required thrust for replacing the front rotor of a modern CROR, but with increased swirl relative to the analyzed conventional propeller. This is mainly due to the effect of the blade passage unloading one of the Boxprop blade halves near the tip, forcing the blade to be more highly loaded closer to the hub. The swirl generated by the Boxprop could be partially recovered if it is used together with a rear counter-rotating propeller. A Wake Analysis Method (WAM) is presented in this work and is used to quantify the power flows inherent to the flow features of the propeller wake. The power flows can be characterized as propulsively beneficial, recoverable, or pure losses. It has the ability to distinguish the kinetic energies of the tip vortices, wakes, and other disturbances from the flow field. The Wake Analysis Method was applied on the two propellers mentioned earlier, and confirmed that the Boxprop produces 50\% more swirl than the conventional propeller. Additionally, the method very clearly shows the lack of tip vortex on the Boxprop, and the presence of it in the flow field of the conventional propeller.
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