| 1. |
- Shia-Hui, Peng, 1967, et al.
(författare)
-
CAA analysis of a wing section with flap side-edges based on hybrid RANS-LES computation
- 2015
-
Ingår i: 21st AIAA/CEAS Aeroacoustics Conference, AIAA Aviation. - Reston, Virginia : American Institute of Aeronautics and Astronautics. - 9781624103674
-
Konferensbidrag (refereegranskat)abstract
- Based on hybrid RANS-LES computation of the turbulent flow around a double-flapped wing section, CAA (Computational Aero-Acoustics) analysis was conducted using the Curle, the Kirchhoff and the FW-H acoustic analogy methods. The focus was placed on the flow-induced noise due to the flap side-edges (FSE). It was shown that the FSE has triggered extensive unsteady vortex motions and being the most potent noise-generating source with significant pressure fluctuations on the side-edge surface. In the CAA analysis, two integral surfaces, defined by the iso-surface of vorticity magnitude, were verified when using the Kirchhoff and the FW-H methods. The Kirchhoff method is more sensitive to the location of the integral surface. The analysis using the Curle method indicates that the pressure fluctuations on the surface of the main wing and the first flap have made similar contributions to the far-field noise level, while the second flap contributes slightly less. The Kirchhoff and FW-H methods have predicted overall higher noise levels comparing to the Curle method. In the comparison, the result obtained with a stochastic method based on a RANS solution was also involved. The result has clearly demonstrated that, to capture the most potential noise generation in the presence of flap side edges, turbulence-resolving simulations should be incorporated in hybrid CFD/CAA analysis.
|
|
| 2. |
|
|
| 3. |
- Lejon, Marcus, 1986, et al.
(författare)
-
Simulation of Tip-Clearance Effects in a Transonic Compressor
- 2015
-
Ingår i: ASME Turbo Expo 2015: Turbine Technical Conference and Exposition. - 9780791856635 ; 2A
-
Konferensbidrag (refereegranskat)abstract
- Tip clearance flow can have a large impact on compressor performance and is therefore important to consider in compressor design. A wide range of computational approaches can be used for modeling tip clearance flow. The different modeling strategies reflect compromises between accuracy and computational time. The present study investigates a large tip gap configuration (1.65% of the rotor tip chord) of the highly loaded transonic 1.5 stage compressor Hulda. The aim of the study is to evaluate different modeling approaches and find a method that can predict the effects of a large tip clearance on compressor performance. The modeling approaches investigated are the SAS-SST model in CFX and the k-ε turbulence model using a wall function and Chien’s low-Reynolds model in the in-house CFD solver VolSol++. Results obtained using the chosen solvers and turbulence models are compared with experimental data, and all approaches are shown to predict the overall performance trends. However, the turbulence kinetic energy in the tip clearance flow and the trajectory of the vortex are shown to vary depending on the method. The SAS-SST model predicts the performance well in terms of total pressure ratio, polytropic efficiency as well as radial distribution of total pressure downstream the rotor. Based on the results from the study, SAS-SST is concluded to be a good candidate for detailed studies of transonic compressors with large tip gaps.
|
|
| 4. |
- Strawbridge, Rona J., et al.
(författare)
-
Identification of a novel proinsulin-associated SNP and demonstration that proinsulin is unlikely to be a causal factor in subclinical vascular remodelling using Mendelian randomisation
- 2017
-
Ingår i: Atherosclerosis. - : Elsevier BV. - 0021-9150 .- 1879-1484. ; 266, s. 196-204
-
Tidskriftsartikel (refereegranskat)abstract
- Background and aims: Increased proinsulin relative to insulin levels have been associated with subclinical atherosclerosis (measured by carotid intima-media thickness (cIMT)) and are predictive of future cardiovascular disease (CVD), independently of established risk factors. The mechanisms linking proinsulin to atherosclerosis and CVD are unclear. A genome-wide meta-analysis has identified nine loci associated with circulating proinsulin levels. Using proinsulin-associated SNPs, we set out to use a Mendelian randomisation approach to test the hypothesis that proinsulin plays a causal role in subclinical vascular remodelling.Methods: We studied the high CVD-risk IMPROVE cohort (n = 3345), which has detailed biochemical phenotyping and repeated, state-of-the-art, high-resolution carotid ultrasound examinations. Genotyping was performed using Illumina Cardio-Metabo and Immuno arrays, which include reported proinsulin-associated loci. Participants with type 2 diabetes (n = 904) were omitted from the analysis. Linear regression was used to identify proinsulin-associated genetic variants.Results: We identified a proinsulin locus on chromosome 15 (rs8029765) and replicated it in data from 20,003 additional individuals. An 11-SNP score, including the previously identified and the chromosome 15 proinsulin-associated loci, was significantly and negatively associated with baseline IMTmean and IMTmax (the primary cIMT phenotypes) but not with progression measures. However, MR-Eggers refuted any significant effect of the proinsulin-associated 11-SNP score, and a non-pleiotropic SNP score of three variants (including rs8029765) demonstrated no effect on baseline or progression cIMT measures.Conclusions: We identified a novel proinsulin-associated locus and demonstrated that whilst proinsulin levels are associated with cIMT measures, proinsulin per se is unlikely to have a causative effect on cIMT.
|
|
| 5. |
- Yao, Huadong, 1982, et al.
(författare)
-
Aero-acoustic analysis and assessment of conceptual low-noise airframe configurations
- 2015
-
Ingår i: 2nd GRAIN2 Open Workshop and Mid-term Review 'Greening Aviation – A Global Challenge' Xi'an, China, 5th - 8th May 2015.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- High-lift (HL) configuration represents a significant part of airframe noise. Two different low-noise HL designs have been assessed with respect to a baseline HL configuration, which is a full-scale regional aircraft wing with a double-slotted part-span flap. The first design uses a single slotted flap. The second design, with a single slotted flap, has invoked a Krueger flap. Hybrid CFD/CAA analysis has been performed using acoustic analogies (the Kirchhoff, FW-H and Curle methods) based on hybrid RANS/-LES computations. It is shown that the Krueger flap has the best aerodynamic and aero-acoustic performances, which haves led to a noise reduction by 6-10dB. One of energetic airframe noise sources is associated to turbulent flow motion over the flap side-edge (FSE). To reduce FSE noise, a fence is attached onto the side edge. In the analysis of this configuration, an effective stochastic noise generation and radiation (SNGR) method was used, which formulates the noise sources based on the RANS solutions computations. The Lighthill acoustic analogy and boundary element method (BEM) in frequency domain have been employed for noise prediction. The analysis shows that the fence is able to effectively reduce noise by about 7dB. Another dominant airframe noise source is the turbulent flow induced by a landing gear (LG). Four low-noise conceptual designs are investigated for a full-scale main landing gear (MLG). The LG-bay door is opened to explore its noise scattering effect. Several different concepts measures for noise reduction have been investigated, including fairing, shallow LG-bay and acoustic liners. The aero-acoustic analysis has been demonstrated that, with a lined bay rear wall, the noise level has been was reduced by 1.817dBA. In the presentation, the aero-acoustic analysis and assessment on the aforementioned airframe configurations will be reporteds and discussed.
|
|
| 6. |
- Yao, Huadong, 1982, et al.
(författare)
-
Assessment of Flap Side-Edge Fence Noise using SNGR Method
- 2016
-
Ingår i: 21st AIAA/CEAS Aeroacoustics Conference, 2015; Dallas; United States; 22 June 2015 through 26 June 2015. - Reston, Virginia : American Institute of Aeronautics and Astronautics.
-
Konferensbidrag (refereegranskat)abstract
- In this paper, the noise reduction efficiency of a flap side-edge fence is revisited and investigated using the stochastic noise generation and radiation (SNGR) method coupled with the Reynolds averaged Navier-Stokes equations (RANS). The configurations are of full scale. The baseline configuration is slotted with double flaps. The fence is attached onto both side edges of the flaps for the purpose of suppressing turbulent vortices induced by the side edge. Furthermore, the efficiency of the SNGR method is assessed as a fast prediction approach for the flap side-edge noise. The noise generation in the SNGR method employs the stochastic model to construct a synthetic turbulent field and takes advantage of the acoustic analogy to formulate the noise sources. The wave equation for the noise radiation is computed by means of the boundary element method (BEM) in frequency space. The BEM takes into account the noise scattered by the surfaces. The fences are found to be efficient for depressing the wake produced by the side edges of the double slotted flaps. Since the energetic vortices contained in the wake are the major contributor of the noise generation, the fence enable an effective noise reduction, particularly in the low frequencies below 200 Hz.
|
|
| 7. |
- Yao, Huadong, 1982, et al.
(författare)
-
Noise radiated by low-Reynolds number flows past a hemisphere at Ma=0.3
- 2017
-
Ingår i: Physics of Fluids. - : AIP Publishing. - 1070-6631 .- 1089-7666. ; 29:7, s. Article no 076102 -
-
Tidskriftsartikel (refereegranskat)abstract
- Flows past a hemisphere and their noise generation are investigated at the Reynolds numbers (Re) of 1000 and 5000. The Mach number is 0.3. The computational method of the flows is large eddy simulation. The noise is computed using the Ffowcs Williams and Hawkings Formulation 1C (F1C). An integral surface with an open end is defined for the F1C. The end surface is removed to reduce the numerical contamination that is introduced by vortices passing this surface. However, the contamination cannot be completely reduced since a discontinuity of the flow quantities still exists at the open surface boundary. This problem is solved using a surface correction method, in which a buffer zone is set up at the end of the integral surface. The transformation of flow structures due to Re is explored. Large coherent structures are observable at low Re, whereas they diminish at high Re. A large amount of small-scale turbulent vortices occur in the latter case. It is found that these characteristics of the flows have an important influence on the noise generation in regard to the noise spectra. In the flows studied in this work, the fluctuating pressure on the walls is a negligible noise contributor as compared with the wake.
|
|
| 8. |
- Abou-Taouk, Abdallah, 1982, et al.
(författare)
-
CFD analysis and application of dynamic mode decomposition for resonant-mode identification and damping in an SGT-100 DLE combustion system
- 2015
-
Ingår i: Proceedings of the 7th European Combustion Meeting. - 9789631212570
-
Konferensbidrag (refereegranskat)abstract
- This paper presents result of a turbulent reacting flow simulation based on a hybrid Unsteady Reynolds Averaged Navier Stokes/Large Eddy Simulation model (Menter’s SAS-SST model) applied to an experimental version of an industrial gas turbine combustion chamber at a pressure of 6 bar. The kinetics were represented by a recently developed in-house 4-step reaction mechanism using 7 species. A reasonably good agreement with measurements is found concerning velocity, temperature, pressure loss, mixture fraction and fuel mass fraction. The dynamic mode decomposition algorithm is also used here in order to identify some resonant modes and to quantify their respective frequency and damping. A number of low frequency modes with combustion dynamics included are observed and compared with the measurements.
|
|
| 9. |
- Abou-Taouk, Abdallah, 1982, et al.
(författare)
-
CFD analysis of a SGT-800 burner in a combustion RIG
- 2016
-
Ingår i: ASME Turbo Expo, June 13 – 17, 2016, Seoul, South Korea.
-
Konferensbidrag (refereegranskat)abstract
- This work focuses on 3D turbulent reacting flow modeling of a SGT-800 3rd generation dry low emission (DLE) burner at both atmospheric and engine-like conditions. At atmospheric pressure the burner is fitted in a test rig with high pre-heating of the incoming air. To reduce the computational cost, the M4 mechanism previously developed by Abou-Taouk et al. (2013) is used for operating pressure of 1 bar. A new novel optimized 4-step reaction mechanism for methane-air mixture is developed in the present work at an operating pressure of 20 bar. The mechanism is based on a large sample of detailed chemistry solutions that are processed by an iterative optimization procedure. This leads to a reduced 4-step mechanism, reproducing the targeted detailed chemistry solutions in terms of laminar flame speeds, species profiles and temperatures. The CFD simulations are performed using the combined eddy dissipation model / finite rate chemistry (EDM/FRC) turbulence chemistry interaction model. The turbulence is modeled using both the k-ω SST and the scale adaptive simulation (SAS) turbulence models. A comprehensive testing and measurement campaign carried out at atmospheric pressure for this burner was previously performed in a combustion test rig. The CFD results are compared to measurement data which includes for example flame position and pressure drop.
|
|
| 10. |
- Abou-Taouk, Abdallah, 1982, et al.
(författare)
-
CFD investigation of a Stirling engine f exi-fuel burner based on MILD combustion
- 2015
-
Ingår i: Proceedings of the International Symposium on Turbulence, Heat and Mass Transfer. - 2377-2816. ; 0, s. 855-858
-
Konferensbidrag (refereegranskat)abstract
- This paper presents the comparison of results from tests and 3D CFD combustion simulations based on both RANS and hybrid URANS/LES (SAS-SST model) turbulence models applied to an industrial Stirling engine combustion chamber at atmospheric pressure. Both natural gas and landf ll gas mixture were simulated. The combustor is designed to operate in the MILD combustion mode which is characterized by low f ame temperatures and low NOX emissions. The kinetics for the landf ll gas was represented by a new optimized 4-step global mechanism, named AAT4NR, which was optimized for the present landf ll mixture. The new mechanism is developed using well-established optimization tools, where the coeff cients of the 4-step global chemistry are determined from a set of reference detailed chemistry solutions. A good agreement with measurements is found concerning major emissions, temperatures and NOX-levels.
|
|
| 11. |
- Abou-Taouk, Abdallah, 1982, et al.
(författare)
-
CFD investigation of a Stirling engine flexi-fuel burner based on MILD combustion
- 2015
-
Ingår i: Turbulence, Heat and Mass Transfer 8. - 2377-2816. - 9781567004274 ; 8
-
Konferensbidrag (refereegranskat)abstract
- This paper presents comparisons of results from tests and 3D CFD combustion simulations based on both RANS and hybrid URANS/LES (SAS-SST model) turbulence models applied to an industrial Stirling engine combustion chamber at atmospheric pressure. Both methane gas and landfill gas were simulated. The combustor is designed to operate in the MILD combustion mode which is characterized by low flame temperatures and low NOx emissions. A 4-step reduced reaction mechanism, named AAT4NR, involving seven species was developed to represent the landfill gas. The optimization was performed at atmospheric pressure for a range of fresh gas temperatures [300 K - 1000 K] and equivalence ratios [0.15 - 1]. Comparisons with detailed chemistry solutions of a planar propagating flame front show that the laminar flame speed, the adiabatic flame temperature, the ignition delay time and the species concentration at equilibrium are adequately predicted. There is good agreement between the quantities predicted with URANS/LES and experimental data, in terms of flow and flame dynamics, averaged temperatures, NOX-levels and the concentrations of some major species.
|
|
| 12. |
- Abou-Taouk, Abdallah, 1982, et al.
(författare)
-
Optimized Reduced Chemistry and Molecular Transport for Large Eddy Simulation of Partially Premixed Combustion in a Gas Turbine
- 2016
-
Ingår i: Combustion Science and Technology. - : Informa UK Limited. - 0010-2202 .- 1563-521X. ; 188:1, s. 21-39
-
Tidskriftsartikel (refereegranskat)abstract
- A methodology is discussed to automatically determine the parameters of closed budget equations for chemical species mass fractions and energy, in order to simulate spatially filtered flames as required in large eddy simulation (LES). The method accounts for the effects of LES filtering on chemistry and transport by simultaneously optimizing, for a reduced number of species, the Arrhenius reaction rates and a correction to mixture-averaged molecular diffusion coefficients. The objective is to match, for a given filter size, spatially filtered canonical one-dimensional flames simulated with detailed chemistry solutions. This approach is designed for quite well-resolved LES, in which most of the unresolved fluctuations result from flame thickening due to spatial filtering, thus featuring weak levels of sub-grid scale flame wrinkling. Methane-air partially premixed combustion is addressed. A four-step reduced reaction mechanism involving seven species is developed along with mass and heat molecular transport properties. The optimization is performed at atmospheric pressure and at 3 bar, for ranges of fresh gas temperatures [300–650 K] and equivalence ratios [0.4–1.2]. Comparisons with the filtered detailed chemistry solution of a planar propagating front show that the laminar flame speed, the adiabatic flame temperature, the species profiles in the reaction zone, and the flow chemical composition and temperature at equilibrium are adequately predicted. The new sub-grid scale modeling approach is then applied to three-dimensional LES of an industrial gas turbine burner. Good agreement is found between the quantities predicted with LES and experimental data, in terms of flow and flame dynamics, axial velocities, averaged temperatures, and some major species concentrations. Results are also improved compared to previous simulations of the same burner.
|
|
| 13. |
- Andersson, Niklas, 1976, et al.
(författare)
-
Numerical Simulation of Stirling Engines Using an Unsteady Quasi-One-Dimensional Approach
- 2015
-
Ingår i: Journal of Fluids Engineering, Transactions of the ASME. - : ASME International. - 1528-901X .- 0098-2202. ; 137:5, s. Art. no. 051104-
-
Tidskriftsartikel (refereegranskat)abstract
- An existing computer code for solving the quasi-one-dimensional flow equations governing unsteady compressible flow in tubes with smoothly varying cross-section areas, has been adapted to the simulation of the oscillatory flow in Stirling engines for engine design purposes. By utilizing an efficient smoothing algorithm for the area function that preserves the total volume of the tube, it has been possible to achieve a highly accurate and fully conservative numerical scheme. Sub-models for wall friction and heat transfer have been added, enabling the simulation of gas heaters, gas coolers, and regenerators. The code has been used for the modeling of an alpha-type Stirling engine and validated for a range of operating conditions with good results.
|
|
| 14. |
- Cuppoletti, Daniel, et al.
(författare)
-
Elimination of shock associated noise in supersonic jets by destructive wave interference
- 2018
-
Ingår i: AIAA Aerospace Sciences Meeting, 2018. - Reston, Virginia : American Institute of Aeronautics and Astronautics.
-
Konferensbidrag (refereegranskat)abstract
- A novel application of fluidic injection was developed to investigate and understand the effects of discrete fluidic injection internal to the jet nozzle. Various injection locations, angles, and conditions were studied resulting in unique acoustic behavior and flow field modifications. For most conditions the acoustics are relatively unaffected or increased, but for very specific conditions noise was drastically decreased. For optimized conditions the shock noise was completely eliminated and in other cases a jet instability was generated that significantly decreased high frequency noise. Measurements of the velocity field indicated that shock interaction due to shocks from the injection jet interact with the primary jet shocks, and significantly reduce the shock strength, attributing massive shock noise reduction. Validation of the experimental results was achieved with LES, which provided additional insight into the shock suppression due to resolution of the flowfield internal to the nozzle. Optimal injection parameters resulted in reduction of OASPL of -7 dB at the upstream and downstream angles simultaneously through a combination of shock disruption and streamwise vorticity introduction. A new mechanism of supersonic jet noise reduction, destructive interference of the shock structure in the jet is reported.
|
|
| 15. |
- Cuppoletti, Daniel, et al.
(författare)
-
Elimination of Shock-Associated Noise in Supersonic Jets by Destructive Wave Interference
- 2019
-
Ingår i: AIAA Journal. - 1533-385X .- 0001-1452. ; 57:2, s. 720-734
-
Tidskriftsartikel (refereegranskat)abstract
- A novel application of fluidic injection was developed to investigate and understand the effects of discrete fluidic injection internal to the jet nozzle. Various injection locations, angles, and conditions were studied, resulting in unique acoustic behavior and flowfield modifications. For most conditions, the acoustics are relatively unaffected or increased, but for very specific conditions, noise was drastically decreased. For optimized conditions, the shock noise was completely eliminated, and in other cases, a jet instability was generated that significantly decreased high-frequency noise. Measurements of the velocity field indicated that shock interaction, due to shocks from the injection jets, interacts with the primary jet shocks and significantly reduces the shock strength, attributing massive shock noise reduction. Validation of the experimental results was achieved with large-eddy simulation, which provided additional insight into the shock suppression due to resolution of the flowfield internal to the nozzle. Optimal injection parameters resulted in reduction of overall sound pressure level of -7 d B at the upstream and downstream angles simultaneously through a combination of shock disruption and streamwise vorticity introduction. A new mechanism of supersonic jet noise reduction and destructive interference of the shock structure in the jet is reported.
|
|
| 16. |
- Hafsteinsson, Haukur, 1984, et al.
(författare)
-
Noise Control of Supersonic Jet with Steady and Flapping Fluidic Injection
- 2015
-
Ingår i: AIAA Journal. - 1533-385X .- 0001-1452. ; 53:11, s. 3251-3272
-
Tidskriftsartikel (refereegranskat)abstract
- Large-eddy simulation is used to investigate steady-state mass flow injection into a supersonic jet stream with and without flapping motion of the microjets. The results are validated with particle image velocimetry and acoustic measurements. The effect of microjet penetration on the far-field acoustics is studied by altering the number of injectors, the cross-sectional area of each injector, and the injection mass flow. The injectors are evenly distributed around the nozzle exit. The injection angle is 90 deg relative to the main jet flow. This research is a continuation of a previous large-eddy simulation study of pulsed injection that showed that the unsteady injection-induced pressure pulses in the jet caused increased tonal noise for far-field observers at low angles. Flapping jet injection was shown to minimize the creation of the pressure pulses, except for high-amplitude flapping angles and high injection mass flows, where the injections divert out of the shear layer and introduce periodic superposition of the double shock-cell structure. Furthermore, the flapping injection did not show improved noise reduction compared with the steady injection, which is essentially promising because steady injection proves to be a more practical solution for implementation in real jet engine applications.
|
|
| 17. |
- Manning, Alisa, et al.
(författare)
-
A Low-Frequency Inactivating AKT2 Variant Enriched in the Finnish Population Is Associated With Fasting Insulin Levels and Type 2 Diabetes Risk
- 2017
-
Ingår i: Diabetes. - : AMER DIABETES ASSOC. - 0012-1797 .- 1939-327X. ; 66:7, s. 2019-2032
-
Tidskriftsartikel (refereegranskat)abstract
- To identify novel coding association signals and facilitate characterization of mechanisms influencing glycemic traits and type 2 diabetes risk, we analyzed 109,215 variants derived from exome array genotyping together with an additional 390,225 variants from exome sequence in up to 39,339 normoglycemic individuals from five ancestry groups. We identified a novel association between the coding variant (p.Pro50Thr) in AKT2 and fasting plasma insulin (FI), a gene in which rare fully penetrant mutations are causal for monogenic glycemic disorders. The low-frequency allele is associated with a 12% increase in FI levels. This variant is present at 1.1% frequency in Finns but virtually absent in individuals from other ancestries. Carriers of the FI-increasing allele had increased 2-h insulin values, decreased insulin sensitivity, and increased risk of type 2 diabetes (odds ratio 1.05). In cellular studies, the AKT2-Thr50 protein exhibited a partial loss of function. We extend the allelic spectrum for coding variants in AKT2 associated with disorders of glucose homeostasis and demonstrate bidirectional effects of variants within the pleckstrin homology domain of AKT2.
|
|
