Journal articles: 'K-omega turbulence model'

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Adanta, Dendy, I. M. Rizwanul Fattah, and Nura Musa Muhammad. "COMPARISON OF STANDARD k-epsilon AND SST k-omega TURBULENCE MODEL FOR BREASTSHOT WATERWHEEL SIMULATION." Journal of Mechanical Science and Engineering 7, no. 2 (October 9, 2020): 039–44. http://dx.doi.org/10.36706/jmse.v7i2.44.

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Currently, Computational Fluid Dynamics (CFD) was utilized to predict the performance, geometry optimization or physical phenomena of a breastshot waterwheel. The CFD method requires the turbulent model to predict the turbulent flow. However, until now there is special attention on the effective turbulent model used in the analysis of breastshot waterwheel. This study is to identify the suitable turbulence model for a breatshot waterwheel. The two turbulence models investigated are: standard k-epsilon model and shear stress transport (SST) k-omega. Pressure based and one degrees of freedom (one-DoF) feature was used in this case with 75 Nm, 150 Nm, 225 Nm and 300 Nm as preloads. Based on the results, the standard k-epsilon model gave similar result with the SST k-omega model. Therefore, the simulation for breastshot waterwheel will be efficient if using the standard k-epsilon model because it requires lower computational power than the SST k-omega model. However, to study about physical phenomenon, the SST k-omega model is recommend.

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Azorakos, Georgios, Bjarke Eltard Larsen, and David R. Fuhrman. "NEW METHODS FOR STABILIZING RANS TURBULENCE MODELS WITH APPLICATION TO LARGE SCALE BREAKING WAVES." Coastal Engineering Proceedings, no. 36v (December 28, 2020): 19. http://dx.doi.org/10.9753/icce.v36v.waves.19.

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Recently, Larsen and Fuhrman (2018) have shown that seemingly all commonly used (both k-omega and k-epsilon variants) two-equation RANS turbulence closure models are unconditionally unstable in the potential flow beneath surface waves, helping to explain the wide-spread over-production of turbulent kinetic energy in CFD simulations, relative to measurements. They devised and tested a new formally stabilized formulation of the widely used k-omega turbulence model, making use of a modified eddy viscosity. In the present work, three new formally-stable k-omega turbulence model formulations are derived and tested in CFD simulations involving the flow and dynamics beneath large-scale plunging breaking waves.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/T2fFRgq3I8E

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Choi, Sung-Woong, Hyoung-Seock Seo, and Han-Sang Kim. "Analysis of Flow Characteristics and Effects of Turbulence Models for the Butterfly Valve." Applied Sciences 11, no. 14 (July 8, 2021): 6319. http://dx.doi.org/10.3390/app11146319.

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In the present study, the flow characteristics of butterfly valves with different sizes DN 80 (nominal diameter: 76.2 mm), DN 262 (nominal diameter: 254 mm), DN 400 (nominal diameter: 406 mm) were numerically investigated under different valve opening percentages. Representative two-equation turbulence models of two-equation k-epsilon model of Launder and Sharma, two-equation k-omega model of Wilcox, and two-equation k-omega SST model of Menter were selected. Flow characteristics of butterfly valves were examined to determine turbulence model effects. It was determined that increasing turbulence effect could cause many discrepancies between turbulence models, especially in areas with large pressure drop and velocity increase. In addition, sensitivity analysis of flow properties was conducted to determine the effect of constants used in each turbulence model. It was observed that the most sensitive flow properties were turbulence dissipation rate (Epsilon) for the k-epsilon turbulence model and turbulence specific dissipation rate (Omega) for the k-omega turbulence model.

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Canbolat, Gökhan, Alperen Yıldızeli, Haluk Anıl Köse, and Sertaç Çadırcı. "Numerical Investigation of Transitional Flow over a Flat Plate under Constant Heat Fluxes." Academic Perspective Procedia 1, no. 1 (November 9, 2018): 187–95. http://dx.doi.org/10.33793/acperpro.01.01.39.

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In this study, a boundary layer flow over a flat plate is investigated numerically at constant inlet freestream velocity and turbulence intensity. After intensive mesh refinements, an adequate computational domain is determined. Four turbulence models (k-epsilon, k-omega, k-omega SST, Transition SST) are used to analyze the boundary layer flow. Local surface friction coefficient distribution is obtained and compared to each other to assess the most convenient turbulence model. The Computational Fluid Dynamics (CFD) results show that the Transition SST turbulence model demonstrates the most realistic surface friction coefficient (Cf) distribution in agreement with the experimental data. Additionally; the effects of constant heat fluxes on Cf values are investigated and it is found that the heating process moves transition backward compared to isothermal case. Moreover, it is fount that Cf values in the turbulent region decrease compared to isothermal case.

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Zalesny, V. B., and S. N. Moshonkin. "Sensitivity of the ocean circulation model to the k–omega vertical turbulence parametrization." Известия Российской академии наук. Физика атмосферы и океана 55, no. 5 (November 25, 2019): 103–13. http://dx.doi.org/10.31857/s0002-3515555103-113.

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Ocean general circulation model (OGCM) of the INM RAS with embedded k turbulent model is developed. The solution of the k model equations depends on the frequencies of buoyancy and velocity shift which are generated by the OGCM. The coefficients of vertical turbulence in OGCM depend on k and omega. The numerical algorithms of both models are based on the splitting method for physical processes. The model equations are split into two stages, describing the three-dimensional transport-diffusion of the kinetic energy of turbulence and frequency and their local generation-dissipation. The system of ordinary differential equations arising at the second stage is solved analytically, which ensures the efficiency of the algorithm. Analytical solution also written for the vertical turbulence coefficient equation. The model is used to study the sensitivity of the model circulation of the North AtlanticArctic Ocean to variations in the parameters of vertical turbulence. Experiments show that varying the coefficients of the analytical model solution can improve the adequacy of the simulation.

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Menter, F. R. "Influence of freestream values on k-omega turbulence model predictions." AIAA Journal 30, no. 6 (June 1992): 1657–59. http://dx.doi.org/10.2514/3.11115.

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Ramadhan Al-Obaidi, Ahmed. "Effects of Different Turbulence Models on Three-Dimensional Unsteady Cavitating Flows in the Centrifugal Pump and Performance Prediction." International Journal of Nonlinear Sciences and Numerical Simulation 20, no. 3-4 (May 26, 2019): 487–509. http://dx.doi.org/10.1515/ijnsns-2018-0336.

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AbstractIn centrifugal pumps, it is important to select appropriate turbulence model for the numerical simulation in order to obtain reliable and accurate results. In this work, ten turbulence models in 3-D transient simulation for the centrifugal pump are chosen and compared. The pump performance is validated with experimental results. The numerical results reveal that the SST turbulence model was closer to the experimental results in predicting head. In addition, the pressure variation trend for the ten models is very similar which increases and then decreases from the inlet to outlet of the pump along the streamline. The SST k-ω model predicts the performance of the pump was more accurately than other turbulent models. Furthermore, the results also found that the error is the least at design operation condition 300(l/min), which is around 1.98 % for the SST model and 2.14 % and 2.38 % for the LES and transition omega model. Within 7.61 %, the errors at higher flow rate 350(l/min) for SST. The error for SST model is smaller as compared to different turbulent models. For the Realizable k-ɛ model, the errors fluctuate were more high than other models.

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Thivet, F., M. Daouk, and D. Knight. "Influence of the wall condition on k-omega turbulence model predictions." AIAA Journal 40 (January 2002): 179–81. http://dx.doi.org/10.2514/3.15014.

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Moshonkin, Sergey, Vladimir Zalesny, and Anatoly Gusev. "Simulation of the Arctic—North Atlantic Ocean Circulation with a Two-Equation K-Omega Turbulence Parameterization." Journal of Marine Science and Engineering 6, no. 3 (August 18, 2018): 95. http://dx.doi.org/10.3390/jmse6030095.

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The results of large-scale ocean dynamics simulation taking into account the parameterization of vertical turbulent exchange are considered. Numerical experiments were carried out using k − ω turbulence model embedded to the Institute of Numerical Mathematics Ocean general circulation Model (INMOM). Both the circulation and turbulence models are solved using the splitting method with respect to physical processes. We split k − ω equations into the two stages describing transport-diffusion and generation-dissipation processes. At the generation-dissipation stage, the equation for ω does not depend on k. It allows us to solve both turbulence equations analytically that ensure high computational efficiency. The coupled model is used to simulate the hydrophysical fields of the North Atlantic and Arctic Oceans for 1948–2009. The model has a horizontal resolution of 0.25 ∘ and 40 σ -levels along the vertical. The numerical results show the model’s satisfactory performance in simulating large-scale ocean circulation and upper layer dynamics. The sensitivity of the solution to the change in the coefficients entering into the analytical solution of the k − ω model which describe the influence of some physical factors is studied. These factors are the climatic annual mean buoyancy frequency (AMBF) and Prandtl number as a function of the Richardson number. The experiments demonstrate that taking into account the AMBF improves the reproduction of large-scale ocean characteristics. Prandtl number variations improve the upper mixed layer depth simulation.

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Kok, Johan C. "Resolving the dependence on freestream values for the k-omega turbulence model." AIAA Journal 38 (January 2000): 1292–95. http://dx.doi.org/10.2514/3.14547.

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Balabel, Ashraf, Mohammad Faizan, and Ali Alzaed. "Towards a Computational Fluid Dynamics-Based Fuzzy Logic Controller of the Optimum Windcatcher Internal Design for Efficient Natural Ventilation in Buildings." Mathematical Problems in Engineering 2021 (April 10, 2021): 1–10. http://dx.doi.org/10.1155/2021/9936178.

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Recently, increased attention has been given to the coupling of computational fluid dynamics (CFD) with the fuzzy logic control system for obtaining the optimum prediction of many complex engineering problems. The data provided to the fuzzy system can be obtained from the accurate computational fluid dynamics of such engineering problems. Windcatcher performance to achieve thermal comfort conditions in buildings, especially in hot climate regions, is considered as one such complex problem. Windcatchers can be used as natural ventilation and passive cooling systems in arid and windy regions in Saudi Arabia. Such systems can be considered as the optimum solution for energy-saving and obtaining thermal comfort in residential buildings in such regions. In the present paper, three-dimensional numerical simulations for a newly-developed windcatcher model have been performed using ANSYS FLUENT-14 software. The adopted numerical algorithm is first validated against previous experimental measurements for pressure coefficient distribution. Different turbulence models have been firstly applied in the numerical simulations, namely, standard k-epsilon model (1st and 2nd order), standard Wilcox k-omega model (1st and 2nd order), and SST k-omega model. In order to assess the accuracy of each turbulence model in obtaining the performance of the proposed model of the windcatcher system, it is found that the second order k-epsilon turbulence model gave the best results when compared with the previous experimental measurements. A new windcatcher internal design is proposed to enhance the ventilation performance. The fluid dynamics characteristics of the proposed model are presented, and the ventilation performance of the present model is estimated. The numerical velocity profiles showed good agreement with the experimental measurements for the turbulence model. The obtained results have shown that the second order k-epsilon turbulence can predict the different important parameters of the windcatcher model. Moreover, the coupling algorithm of CFD and the fuzzy system for obtaining the optimum operating parameters of the windcatcher design are described.

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Chima, Rodrick V. "Application of the k-omega turbulence model to quasi-three-dimensional turbomachinary flows." Journal of Propulsion and Power 12, no. 6 (November 1996): 1176–79. http://dx.doi.org/10.2514/3.24159.

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13

Zheng, Xiaoqing, and Feng Liu. "Staggered upwind method for solving Navier-Stokes and k-omega turbulence model equations." AIAA Journal 33, no. 6 (June 1995): 991–98. http://dx.doi.org/10.2514/3.12808.

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14

Choi, Chang H., and Jung Y. Yoo. "Cascade-flow calculations using the k-omega turbulence model with explicit-implicit solver." AIAA Journal 35 (January 1997): 1551–52. http://dx.doi.org/10.2514/3.13707.

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Hellsten, Antti, and Seppo Laine. "Extension of k-omega shear-stress transport turbulence model for rough-wall flows." AIAA Journal 36 (January 1998): 1728–29. http://dx.doi.org/10.2514/3.14029.

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Grunloh, Timothy P. "Four equation k-omega based turbulence model with algebraic flux for supercritical flows." Annals of Nuclear Energy 123 (January 2019): 210–21. http://dx.doi.org/10.1016/j.anucene.2018.09.024.

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Habib, Merouane. "Prediction of a Turbulent Flow in Bluff Body Stabilized Burner by Using Two Classical Models of Turbulence." International Journal of Engineering Research in Africa 32 (September 2017): 112–23. http://dx.doi.org/10.4028/www.scientific.net/jera.32.112.

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In present study, a detailed investigation of an annular jet at high diameter ratio r = 0,905 has been reported numerically. The numerical simulation was performed by making use of the commercial CFD code which discretizes the solution domain into quadrilateral elements and use a numerical finite volume method coupled with a multigrid resolution scheme. In this research the applications of k-epsilon and k-omega models for prediction of a turbulent flow in annular jet are described. The flow governing equations are solved by using a performed coupled algorithm. The results of predicted axial velocity profiles are compared with the experimental data. The computations indicated that the results predicted by k-epsilon model are in good agreement with the experiment.

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Elwekeel, Fifi NM, Qun Zheng, and Antar MM Abdala. "Air/mist cooling in a rectangular duct with varying shapes of ribs." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 228, no. 11 (November 13, 2013): 1925–35. http://dx.doi.org/10.1177/0954406213512295.

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A numerical investigation of turbulent forced convection in a three-dimensional channel with periodic ribs on the lower channel wall is conducted. The lower wall is subjected to a uniform heat flux condition while the upper wall insulated. This study was conducted to investigate the forced convection, flow friction, and performance factor in a horizontal air and air/mist cooled rectangular duct, with various shaped ribs. Calculations are carried out for square ribs (case A), triangular ribs (case B), and trapezoidal ribs (case C and case D) cross sections over a range of Reynolds numbers (8000–20,000), constant mist mass fraction (6%), and fixed rib height and pitch. To investigate turbulence model effects, computations based on a finite volume method are carried out by utilizing three turbulence models: the standard k-ω, Omega Reynolds stress, and shear stress transport turbulence models. The predicted results from using several turbulence models reveal that the shear stress transport turbulence model provides better agreement with available measurements than others. It is found that the average mist cooling enhancement is about 1.8 times. The air/mist provides the higher heat transfer enhancement over air with trapezoidal-shaped ribs (38°, case C).

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Zhang, De-Sheng, Da-Zhi Pan, Hai-Yu Wang, and Wei-Dong Shi. "Numerical prediction of cavitating flow around a hydrofoil using pans and improved shear stress transport k-omega model." Thermal Science 19, no. 4 (2015): 1211–16. http://dx.doi.org/10.2298/tsci1504211z.

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The prediction accuracies of partially-averaged Navier-Stokes model and improved shear stress transport k-? turbulence model for simulating the unsteady cavitating flow around the hydrofoil were discussed in this paper. Numerical results show that the two turbulence models can effectively reproduce the cavitation evolution process. The numerical prediction for the cycle time of cavitation inception, development, detachment, and collapse agrees well with the experimental data. It is found that the vortex pair induced by the interaction between the re-entrant jet and mainstream is responsible for the instability of the cavitation shedding flow.

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Česenek, Jan. "Space-time discontinuous Galerkin method for the numerical simulation of viscous compressible gas flow with the k-omega turbulence model." EPJ Web of Conferences 180 (2018): 02016. http://dx.doi.org/10.1051/epjconf/201818002016.

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In this article we deal with the numerical simulation of the non-stationary compressible turbulent flow described by the Reynolds-Averaged Navier-Stokes (RANS) equations. This RANS system is equipped with two-equation k-omega turbulence model. The discretization of these two systems is carried out separately by the space-time discontinuous Galerkin method. This method is based on the piecewise polynomial discontinuous approximation of the sought solution in space and in time. We use the numerical experiments to demonstrate the applicability of the shown approach. All presented results were computed with the own-developed code.

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Azzouz, El Amin, Samir Houat, and Ahmed Zineddine Dellil. "Numerical Assessment of Turbulent Flow Driving in a Two-Sided Lid-Driven Cavity with Antiparallel Wall Motion." Defect and Diffusion Forum 406 (January 2021): 133–48. http://dx.doi.org/10.4028/www.scientific.net/ddf.406.133.

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In this paper, the case of the steady two-dimensional flow in a two-sided lid-driven square cavity is numerically investigated by the finite volume method (FVM). The flow motion is due to the top and bottom horizontal walls sliding symmetrically in the opposite direction with equal velocities, UT and UB, obtained through three respective Reynolds numbers, Re1,2=10000, 15000, and 20000. Due to the lack of availability of experimental results in this Reynolds number margin for this type of flow, the problem is first examined by considering that the flow is turbulent with the inclusion of four commonly used RANS turbulence models: Omega RSM, SST k-ω, RNG k-ε and Spalart-Allmaras (SA). Next, the regime is considered being laminar in the same range of Reynolds numbers. A systematic evaluation of the flow characteristics is performed in terms of stream-function contour, velocity profiles, and secondary vortices depth. Examination of the calculation results reveals the existence of a great similarity of the predicted flow structures between the Omega RSM model and those from the laminar flow assumption. On the other hand, the computed flow with the SST k-ω model, the RNG k-ε model, and the SA model reveals a remarkable under-prediction which appears clearly in the size and number of secondary vortices in the near-wall regions. Various benchmarking results are presented in this study.

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Azzouz, El Amin, Samir Houat, and Ahmed Zineddine Dellil. "Numerical Assessment of Turbulent Flow Driving in a Two-Sided Lid-Driven Cavity with Antiparallel Wall Motion." Defect and Diffusion Forum 406 (January 2021): 133–48. http://dx.doi.org/10.4028/www.scientific.net/ddf.406.133.

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In this paper, the case of the steady two-dimensional flow in a two-sided lid-driven square cavity is numerically investigated by the finite volume method (FVM). The flow motion is due to the top and bottom horizontal walls sliding symmetrically in the opposite direction with equal velocities, UT and UB, obtained through three respective Reynolds numbers, Re1,2=10000, 15000, and 20000. Due to the lack of availability of experimental results in this Reynolds number margin for this type of flow, the problem is first examined by considering that the flow is turbulent with the inclusion of four commonly used RANS turbulence models: Omega RSM, SST k-ω, RNG k-ε and Spalart-Allmaras (SA). Next, the regime is considered being laminar in the same range of Reynolds numbers. A systematic evaluation of the flow characteristics is performed in terms of stream-function contour, velocity profiles, and secondary vortices depth. Examination of the calculation results reveals the existence of a great similarity of the predicted flow structures between the Omega RSM model and those from the laminar flow assumption. On the other hand, the computed flow with the SST k-ω model, the RNG k-ε model, and the SA model reveals a remarkable under-prediction which appears clearly in the size and number of secondary vortices in the near-wall regions. Various benchmarking results are presented in this study.

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Liu, Fieng, and Xiaoqing Zheng. "Staggered finite volume scheme for solving cascade flow with a k-omega turbulence model." AIAA Journal 32, no. 8 (August 1994): 1589–97. http://dx.doi.org/10.2514/3.12148.

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Choual, Kheireddine, and Redouane Benzeguir. "Simulation of Opposed-Jets Configuration H₂/Air, CH₄/Air." International Letters of Chemistry, Physics and Astronomy 55 (July 2015): 34–46. http://dx.doi.org/10.18052/www.scipress.com/ilcpa.55.34.

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The opposed-jets configuration is very used in industrial systems. The actual practical applications use clean fuels which in stead of classical hydrocarbons. The present work is a numerical simulation of opposed diffusion jets using FLUENT6.3.26. We have compared different turbulence models and combustion models and mechanisms to find which gives the best predictions for this type of flows. We have used methane and hydrogen fuels because they are considered as clean fuels. The comparison between k-ε, k-omega and RSM turbulent models shows that both of k-ε and RSM gives good results. The use of k-ε is more practical because it requires less long time to be implied. The comparison between the combustion models shows that EDC gives more realistic results than eddy dissipation and Finite rate models. In addition, the detailed chemical mechanisms are more adequate to this model. For both methane and hydrogen flames, the detailed mechanisms gives good results and temperatures.

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Nering, Konrad, and Kazimierz Rup. "Modified algebraic model of laminar-turbulent transition for internal flows." International Journal of Numerical Methods for Heat & Fluid Flow 30, no. 4 (January 21, 2019): 1743–53. http://dx.doi.org/10.1108/hff-10-2018-0597.

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Purpose For internal flows with small values of the Reynolds number, there is often at a considerable distance from the pipe inlet cross-section a change of the flow form from laminar to turbulent. To describe this phenomenon of laminar-turbulent transition in the pipe, also parallel-plate channel flow, a modified algebraic intermittency model was used. The original model for bypass transition developed by S. Kubacki and E. Dick was designed for simulating bypass transition in turbomachinery. Design/methodology/approach A modification of mentioned model was proposed. Modified model is suitable for simulating internal flows in pipes and parallel-plate channels. Implementation of the modified model was made using the OpenFOAM framework. Values of several constants of the original model were modified. Findings For selected Reynolds numbers and turbulence intensities (Tu), localization of laminar breakdown and fully turbulent flow was presented. Results obtained in this work were compared with corresponding experimental results available in the literature. It is particularly worth noting that asymptotic values of wall shear stress in flow channels and asymptotic values of axis velocity obtained during simulations are similar to related experimental and theoretical results. Originality/value The modified model allows precision numerical simulation in the area of transitional flow between laminar, intermittent and turbulent flows in pipes and parallel-plate channels. Proposed modified algebraic intermittency model presented in this work is described by a set of two additional partial differential equations corresponding with k-omega turbulence model presented by Wilcox (Wilcox, 2006).

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Česenek, Jan. "Space-time discontinuous Galerkin method for the numerical simulation of the compressible turbulent gas flow through the porous media." EPJ Web of Conferences 213 (2019): 02011. http://dx.doi.org/10.1051/epjconf/201921302011.

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The article is concerned with the numerical simulation of the compressible turbulent gas flow through the porous media using space-time discontinuous Galerkin method.The mathematical model of flow is represented by the system of non-stationary Reynolds-Averaged Navier-Stokes (RANS) equations. The flow through the porous media is characterized by the loss of momentum. This RANS system is equipped with two-equation k-omega turbulence model. The discretization of these two systems is carried out separately by the space-time discontinuous Galerkin method. This method is based on the piecewise polynomial discontinuous approximation of the sought solution in space and in time. We present some numerical experiments to demonstrate the applicability of the method using own-developed code.

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Ofei, Titus Ntow, and Aidil Yunus Ismail. "Eulerian-Eulerian Simulation of Particle-Liquid Slurry Flow in Horizontal Pipe." Journal of Petroleum Engineering 2016 (September 29, 2016): 1–10. http://dx.doi.org/10.1155/2016/5743471.

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In this study, a computational fluid dynamics (CFD) simulation which adopts the inhomogeneous Eulerian-Eulerian two-fluid model in ANSYS CFX-15 was used to examine the influence of particle size (90 μm to 270 μm) and in situ particle volume fraction (10% to 40%) on the radial distribution of particle concentration and velocity and frictional pressure loss. The robustness of various turbulence models such as the k-epsilon (k-ε), k-omega (k-ω), SSG Reynolds stress, shear stress transport, and eddy viscosity transport was tested in predicting experimental data of particle concentration profiles. The k-epsilon model closely matched the experimental data better than the other turbulence models. Results showed a decrease in frictional pressure loss as particle size increased at constant particle volume fraction. Furthermore, for a constant particle volume fraction, the radial distribution of particle concentration increased with increasing particle size, where high concentration of particles occurred at the bottom of the pipe. Particles of size 90 μm were nearly buoyant especially for high particle volume fraction of 40%. The CFD study shows that knowledge of the variation of these parameters with pipe position is very crucial if the understanding of pipeline wear, particle attrition, or agglomeration is to be advanced.

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Wu, Ran Ran, and Ding Fan. "Air Pressure Reducer Modeling by CFD Methodology." Advanced Materials Research 960-961 (June 2014): 547–50. http://dx.doi.org/10.4028/www.scientific.net/amr.960-961.547.

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In this paper, the computational fluid dynamics (CFD) methodology as well as the shear-stress transport (SST) k-omega turbulence model was adopted to model the air pressure reducer (APR). Changing the gas needle’s displacement of APR continuously, the writer obtains the displacement-pressure characteristics of APR. In order to demonstrate the validity of these characteristics, a physical experiment was conducted, which generates another displacement-pressure characteristic. Comparing the two characteristics with a good agreement, it is indicated that the CFD methodology is suitable to study the displacement-pressure characteristics of APR.

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Qiao, Lei, Jun-Qiang Bai, Jia-Kuan Xu, Jing-Lei Xu, and Yang Zhang. "Modeling of Supersonic/Hypersonic Boundary Layer Transition Using a Single-Point Approach." International Journal of Nonlinear Sciences and Numerical Simulation 19, no. 3-4 (June 26, 2018): 263–74. http://dx.doi.org/10.1515/ijnsns-2017-0011.

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AbstractDuring the process of aerodynamic shape design of supersonic and hypersonic space planes, laminar flow design and boundary layer transition prediction play important roles in aero-thermal numerical simulations and aero-thermal protection design. Therefore, in this study, a computational fluid dynamics compatible transition closure model for high speed laminar-to-turbulent transitional flows is formulated with consideration of the analysis results from stability theory. The proposed model contains two transport equations to describe the transition mechanism using local variables. Specifically, the eddy viscosity of laminar fluctuations and intermittency factor are chosen to be the characteristic parameters and modeled by transport equations. Accounting for the dominant instability modes at supersonic/hypersonic conditions, the first- and second- modes are modeled using local variables through the analysis of laminar self-similar boundary layers. Then, the present transition model is applied with compressibility corrected $k$-$\omega$ shear stress transport turbulence model. Thus, as the main significance of the current work, the present model is enabled to capture the overshoot phenomena as well as predict the transition onset position. Finally, comparisons between the predictions using the present model and the wind tunnel experimental results of several well-documented flow cases are provided to validate the proposed transition turbulence model.

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Andric, Jelena, Stefan Lindstrom, Srdjan Sasic, and Håkan Nilsson. "Particle-level simulations of flocculation in a fiber suspension flowing through a diffuser." Thermal Science 21, suppl. 3 (2017): 573–83. http://dx.doi.org/10.2298/tsci160510185a.

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We investigate flocculation in dilute suspensions of rigid, straight fibers in a decelerating flow field of a diffuser. We carry out numerical studies using a particle-level simulation technique that takes into account the fiber inertia and the non-creeping fiber-flow interactions. The fluid flow is governed by the Reynolds-averaged Navier-Stokes equations with the standard k-omega eddy-viscosity turbulence model. A one-way coupling between the fibers and the flow is considered with a stochastic model for the fiber dispersion due to turbulence. The fibers interact through short-range attractive forces that cause them to aggregate into flocs when fiber-fiber collisions occur. We show that ballistic deflection of fibers greatly increases the flocculation in the diffuser. The inlet fiber kinematics and the fiber inertia are the main parameters that affect fiber flocculation in the prediffuser region.

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Iliev, Rossen. "A CFD analysis of the performance characteristics of different Darrieus turbine runners." E3S Web of Conferences 207 (2020): 02012. http://dx.doi.org/10.1051/e3sconf/202020702012.

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This paper presents the capabilities of analyzing different Darrieus wind turbine runners with the computer program Ansys Fluent. A K-omega turbulence model was used in the case of a two-dimensional flow with a suitable computational grid around the profile of the blades. The obtained theoretical performance characteristics were validated on test rig №7 (Wind Turbines) in the Laboratory of Hydropower and Hydraulic Turbomachinery (HEHT Lab) at the Technical University of Sofia. The data analysis shows that it’s possible to predict the performance characteristic and the optimum operating regime of the Darrieus wind turbine.

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Alvarado, Yolitzin, Rosenberg Romero, Juan Carlos García, Adrian del Pozo, Roberto Zenit, and Sergio Alonso Serna. "Using CFD and PIV to investigate rotating cage-related hydrodynamics for CO2 corrosion studies analyzing 2-, 4- and 8-coupons setups." Anti-Corrosion Methods and Materials 66, no. 6 (November 4, 2019): 802–11. http://dx.doi.org/10.1108/acmm-09-2017-1836.

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Purpose The purpose of this study is to evaluate the corrosion in CO2 using Rotating cage (RC) and Computational fluid dynamics (CFD) software. RC experiments were carried out in a CO2 environment, to evaluate corrosion in a C-Mn Steel. CFD software was used to simulate RC flow conditions during the corrosion process, to evaluate wall shear stress. Design/methodology/approach The RC is used as a laboratory tool for studies of accelerated corrosion, according to standard ASTM G184-06. Steel corrosion was studied by means of the RC methodology. The hydrodynamics are solved numerically using CFD. Numerical calculations were performed on a 2D geometry of 8 coupons JG, for speeds of 460 and 230 rpm. The flow was analyzed with vector graphics and velocity profiles. The numerical calculations were validated with experimental measurements of the velocity field obtained with the technique of Particle Image Velocimetry (PIV). Findings Different turbulence models were used, in which CFD simulations were compared with data obtained from PIV. According to this comparison, the best turbulence model was determined. Originality/value It was found that experimental flow speeds have closer values with Spalart–Allmaras modeling than K-epsilon and K-kl-omega.

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Khalaji, E., M. R. Nazari, and Z. Seifi. "2D numerical simulation of impinging jet to the flat surface by $$k - \omega - \overline{{v^{2} }} - f$$ k - ω - v 2 ¯ - f turbulence model." Heat and Mass Transfer 52, no. 1 (October 3, 2015): 127–40. http://dx.doi.org/10.1007/s00231-015-1688-y.

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Rodríguez-Ocampo, Paola Elizabeth, Michael Ring, Jassiel Vladimir Hernández-Fontes, Juan Carlos Alcérreca-Huerta, Edgar Mendoza, and Rodolfo Silva. "CFD Simulations of Multiphase Flows: Interaction of Miscible Liquids with Different Temperatures." Water 12, no. 9 (September 16, 2020): 2581. http://dx.doi.org/10.3390/w12092581.

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The incorporation of new equations to extend the applicability of open-source computational fluid dynamics (CFD) software according to the user’s needs must be complemented with code verification and validation with a representative case. This paper presents the development and validation of an OpenFOAM®-based solver suitable for simulating multiphase fluid flow considering three fluid phases with different densities and temperatures, i.e., two miscible liquids and air. A benchmark “dam-break” experiment was performed to validate the solver. Ten thermistors measured temperature variations in different locations of the experimental model and the temperature time series were compared against those of numerical probes in analogous locations. The accuracy of the temperature field assessment considered three different turbulence models: (a) zero-equation, (b) k-omega (Reynolds averaged simulation; RAS), and (c) large eddy simulation (LES). The simulations exhibit a maximum time-average relative and absolute errors of 9.3% and 3.1 K, respectively; thus, the validation tests proved to achieve an adequate performance of the numerical model. The solver developed can be applied in the modeling of thermal discharges into water bodies.

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Şumnu, Ahmet, İbrahim Halil Güzelbey, and Orkun Öğücü. "Aerodynamic Shape Optimization of a Missile Using a Multiobjective Genetic Algorithm." International Journal of Aerospace Engineering 2020 (June 8, 2020): 1–17. http://dx.doi.org/10.1155/2020/1528435.

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The aim of this paper is to demonstrate the effects of the shape optimization on the missile performance at supersonic speeds. The N1G missile model shape variation, which decreased its aerodynamic drag and increased its aerodynamic lift at supersonic flow under determined constraints, was numerically investigated. Missile geometry was selected from a literature study for optimization in terms of aerodynamics. Missile aerodynamic coefficient prediction was performed to verify and compare with existing experimental results at supersonic Mach numbers using SST k-omega, realizable k-epsilon, and Spalart-Allmaras turbulence models. In the optimization process, the missile body and fin design parameters need to be estimated to design optimum missile geometry. Lift and drag coefficients were considered objective function. Input and output parameters were collected to obtain design points. Multiobjective Genetic Algorithm (MOGA) was used to optimize missile geometry. The front part of the body, the main body, and tailfins were improved to find an optimum missile model at supersonic speeds. The optimization results showed that a lift-to-drag coefficient ratio, which determines the performance of a missile, was improved about 11-17 percent at supersonic Mach numbers.

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Puelles Magán, Guillermo, Wouter Terra, and Andrea Sciacchitano. "Aerodynamics Analysis of Speed Skating Helmets: Investigation by CFD Simulations." Applied Sciences 11, no. 7 (April 1, 2021): 3148. http://dx.doi.org/10.3390/app11073148.

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In this work, we investigate the flow field around speed skating helmets and their associated aerodynamic drag by means of computational fluid dynamics (CFD) simulations. An existing helmet frequently used in competition was taken as a baseline. Six additional helmet designs, as well as the bare-head configuration, were analysed. All the numerical simulations were performed via 3D RANS simulations using the SST k-ω turbulence model. The results show that the use of a helmet always reduces the aerodynamic drag with respect to the bare head configuration. Besides, an optimised helmet design enables a reduction of the skaters aerodynamic drag by 5.9%, with respect to the bare-head configuration, and by 1.6% with respect to the use of the baseline Omega helmet.

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Zhang, Kai, Ali Ghobadian, and Jamshid M. Nouri. "Scale-Resolving Simulation of a Propane-Fuelled Industrial Gas Turbine Combustor Using Finite-Rate Tabulated Chemistry." Fluids 5, no. 3 (July 29, 2020): 126. http://dx.doi.org/10.3390/fluids5030126.

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The scale-resolving simulation of a practical gas turbine combustor is performed using a partially premixed finite-rate chemistry combustion model. The combustion model assumes finite-rate chemistry by limiting the chemical reaction rate with flame speed. A comparison of the numerical results with the experimental temperature and species mole fraction clearly showed the superiority of the shear stress transport, K-omega, scale adaptive turbulence model (SSTKWSAS). The model outperforms large eddy simulation (LES) in the primary region of the combustor, probably for two reasons. First, the lower amount of mesh employed in the simulation for the industrial-size combustor does not fit the LES’s explicit mesh size dependency requirement, while it is sufficient for the SSTKWSAS simulation. Second, coupling the finite-rate chemistry method with the SSTKWSAS model provides a more reasonable rate of chemical reaction than that predicted by the fast chemistry method used in LES simulation. Other than comparing with the LES data available in the literature, the SSTKWSAS-predicted result is also compared comprehensively with that obtained from the model based on the unsteady Reynolds-averaged Navier–Stokes (URANS) simulation approach. The superiority of the SSTKWSAS model in resolving large eddies is highlighted. Overall, the present study emphasizes the effectiveness and efficiency of coupling a partially premixed combustion model with a scale-resolving simulation method in predicting a swirl-stabilized, multi-jets turbulent flame in a practical, complex gas turbine combustor configuration.

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Hu, Xing Jun, Feng Tao Ren, Bo Yang, and Peng Guo. "Effect of Sunroofs and Side Windows on Aerodynamic Characteristics of Transit Bus." Applied Mechanics and Materials 224 (November 2012): 333–37. http://dx.doi.org/10.4028/www.scientific.net/amm.224.333.

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In this paper, k-Omega turbulence model is applied in the numerical simulation of the transit bus, several typical working conditions of the transit bus with windows open at a speed of 10m/s are investigated, and a custom function Q is introduced to characterize the amount of ventilation of each window. The results show that, when the transit bus travels with windows open, the air always flows into the carriage through the middle and rear side windows of the transit bus, and circulates in the carriage and then flows out of the carriage through the front side window. When the bus travels with sunroofs open in leeward mode and side windows open, the amount of ventilation is the maximum. This working condition is the best one when taking both drag coefficient and the amount of ventilation.

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Gagnon, Louis, Marc J. Richard, and Benoît Lévesque. "SIMULATION OF A ROTATING DEVICE THAT REDUCES THE AERODYNAMIC DRAG OF AN AUTOMOBILE." Transactions of the Canadian Society for Mechanical Engineering 35, no. 2 (June 2011): 229–49. http://dx.doi.org/10.1139/tcsme-2011-0014.

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A two-dimensional Computational Fluid Dynamics (CFD) analysis of the Ahmed body is performed using the k-omega-SST turbulence model implemented in the OpenFOAM (OF) software. The analysis is then modified to include a rotating paddle wheel which captures energy from the swirl that forms behind the vehicle. The rotating wheel is implemented using a General Grid Interface (GGI) in the mesh. Flow energy is captured by the wheel and the power generated by the wheel reaches 16.1 W at optimal conditions. Overall drag reductions of up to 7.6% are also found as side-effects of the rotating paddle wheel. Computations are run in parallel on a dual core computer. A mesh of 30,000 cells is used. Y+ values on the walls of the vehicle range from 60 to 500. Tests are run at both fixed and variable paddle wheel angular velocities.

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Svantesson, Jonas L., Mikael Ersson, Matej Imris, and Pär G. Jönsson. "Numerical Analysis of Slag Transfer in the IronArc Process." Metallurgical and Materials Transactions B 51, no. 5 (August 20, 2020): 2171–86. http://dx.doi.org/10.1007/s11663-020-01930-9.

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Abstract The IronArc process is a novel approach to ironmaking which aims to reduce the associated $${\hbox {CO}}_{2}$$ CO 2 emissions. By superheating gas using electricity in a plasma generator (PG) the heat required for the process can be supplied without burning of coke. Reduction of hematite and magnetite ores is facilitated by additions of hydrocarbons from liquid natural gas (LNG). The melting and reduction of ore will produce a molten slag containing 90 pct wüstite, which will be corrosive to most refractory materials. A freeze-lining can prevent refractory wear by separating the molten slag from the refractory. This approach is evaluated in CFD simulations by studying the liquid flow and solidification of the slag using the enthalpy–porosity model in two different slag transfer designs. It was found that a fast moving slag causes a high near-wall turbulence, which prevents solidification in the affected areas. The RSM turbulence model was verified against published experimental research on solidification in flows. It was found to accurately predict the freeze-lining thickness when a steady state was reached, but with lacking accuracy for predicting the time required for formation of said freeze-lining. The results were similar when the $$k{-}\omega $$ k - ω SST model was used. A design with a slower flow causes more solidified material on the walls and can protect all areas of the refractory wall from the corrosive slag. A parameter study was done on the effect of viscosity, mushy zone parameter, heat conductivity and mass flow on the amount of solidified material, thickness of solidified material, heat flux, and wall shear stress. In the current geometry, freeze-linings completely protect the refractory for mass flow rates of up to 3 $${\text {kg}} \, {\text {s}}^{-1},$$ kg s - 1 , and are stable for the expected viscosity (0.05 to 0.3 Pa), heat conductivity (2 $${\text {W}}\, {\text {m}}^{-1}\,{\text {K}}^{-1}),$$ W m - 1 K - 1 ) , and used mushy zone parameter (10,000).

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Mirzaei, M., and A. Sohankar. "Numerical study of convective heat transfer and fluid flow around two side by side square cylinders using $$ k - \omega - \overline{{\upsilon^{2} }} - f $$ k − ω − υ 2 ¯ − f turbulence model." Heat and Mass Transfer 49, no. 12 (August 13, 2013): 1755–69. http://dx.doi.org/10.1007/s00231-013-1216-x.

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Jang, Hyeonmu, Insu Paek, Seungjoo Kim, and Deockjin Jeong. "Performance Prediction and Validation of a Small-Capacity Twisted Savonius Wind Turbine." Energies 12, no. 9 (May 7, 2019): 1721. http://dx.doi.org/10.3390/en12091721.

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In this study, an off-grid–type small wind turbine for street lighting was designed and analyzed. Its performance was predicted using a computational fluid dynamics model. The proposed wind turbine has two blades with a radius of 0.29 m and a height of 1.30 m. Ansys Fluent, a commercial computational fluid dynamics solver, was used to predict the performance, and the k-omega SST model was used as the turbulence model. The simulation result revealed a tip-speed ratio of 0.54 with a maximum power coefficient, or an aerodynamic rotor efficiency of 0.17. A wind turbine was installed at a measurement site to validate the simulation, and a performance test was used to measure the power production. To compare the simulation results obtained from the CFD simulation with the measured electrical power performance, the efficiencies of the generator and the controller were measured using a motor-generator testbed. Also, the control strategy of the controller was found from the field test and applied to the simulation results. Comparing the results of the numerical simulation with the experiment, the maximum power-production error at the same wind speed was found to be 4.32%.

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Djajadiwinata, Eldwin, Shereef Sadek, Shaker Alaqel, Jamel Orfi, and Hany Al-Ansary. "Numerical and One-Dimensional Studies of Supersonic Ejectors for Refrigeration Application: The Significance of Wall Pressure Variation in the Converging Mixing Section." Applied Sciences 11, no. 7 (April 5, 2021): 3245. http://dx.doi.org/10.3390/app11073245.

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This paper studies the pressure variation that exists on the converging mixing section wall of a supersonic ejector for refrigeration application. The objective is to show that the ejector one-dimensional model can be improved by considering this wall’s pressure variation which is typically assumed constant. Computational Fluid Dynamics (CFD) simulations were used to obtain the pressure variation on the aforementioned wall. Four different ejectors were simulated. An ejector was obtained from a published experimental work and used to validate the CFD simulations. The other three ejectors were a modification of the first ejector and used for the parametric study. The secondary mass flow rate, m˙s, was the main parameter to compare. The CFD validation results indicate that the transition SST turbulence model is better than the k-omega SST model in predicting the m˙s. The results of the ejector one-dimensional model were compared before and after incorporating the wall pressure variation. The comparison shows that the effect of the pressure variation is significant at certain operating conditions. Even around 2% change in the average pressure can give around 32% difference in the prediction of m˙s. For the least sensitive case, around 2% change in the average pressure can give around 7% difference in the prediction.

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Kim, Youjin, Galih Bangga, and Antonio Delgado. "Investigations of HAWT Airfoil Shape Characteristics and 3D Rotational Augmentation Sensitivity Toward the Aerodynamic Performance Improvement." Sustainability 12, no. 18 (September 15, 2020): 7597. http://dx.doi.org/10.3390/su12187597.

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This study investigates the impacts of dierent airfoil shapes on the 3D augmentationand power production of horizontal axis wind turbines (HAWTs). The aerodynamic eect fromchanging the leading and trailing edge of the airfoil is the emphasis of the research. Varied powerproduced from modifying sensitivity on 3D augmentations, caused by revamping airfoil shapes, areshown. The 3D correction law, considering the chord to radius ratio and the blades’ pitch angle inthe rotation, is applied to the airfoil lift coecients. The blade element method (BEM) embeddedin the software Qblade with modified lift coecients simulates the power productions of threewind turbines from these airfoils. The comparisons of the boundary layer characteristics, sectionalforces, and inflow angle of the blade sections are calculated. The k-omega SST turbulence model inOpenFoam visualizes the stall and separation of the blades’ 2D section. The airfoils with a roundedleading edge show a reduced stall and separated flow region. The power production is 2.3 timeshigher for the airfoil constructed with a more rounded leading edge S809r and two times higher forthe airfoil S809gx of the symmetric structure.

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Li, Lei, Guoping Huang, and Jie Chen. "Effects of tip-jet on the performance of a ducted fan." Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 234, no. 2 (September 13, 2019): 508–21. http://dx.doi.org/10.1177/0954410019876516.

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Tip-jet technology has potential value for application in vertical take-off and landing or short take-off and landing concept aircraft. The main objective of this current work is to investigate the effects of the tip-jet on the performance of a ducted fan in hover. The overall flow field of the ducted fans with tip-jet was simulated by using the shear-stress transport k-omega turbulence model with a refined high-quality structured grid at various rotational speeds. The comparative analysis of the performances of the ducted fans with different tip-jet locations was carried out. The results indicate that the circulation of the blade with tip-jet is affected by the flow blockage, Coanda effect, and edge-shed vortex. These flow features were formed by the tip-jet. The fan’s thrust could be augmented when the nozzle was a little farther from the blade trailing edge. However, a higher jet flow utility efficiency could be achieved when the nozzle was close to the blade trailing edge.

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Islam, Md Shafiqul, Md Arafat Hasan, and A. B. M. Toufique Hasan. "Numerical Analysis of Bypass Mass Injection on Thrust Vectoring of Supersonic Nozzle." MATEC Web of Conferences 179 (2018): 03014. http://dx.doi.org/10.1051/matecconf/201817903014.

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High speed aerospace applications require rapid control of thrust (i.e. thrust vectoring) in order to achieve better manoeuvrability. Among the existing technologies, shock vector control is one of the efficient ways to achieve thrust vectoring. In the present study, bypass mass injection (passive control) was used to generate shock vectoring in a planar supersonic Converging-Diverging (CD) nozzle. Two diffenrent bypass lines were used to inject mass in the diverging section varying their dimension in the span wise direction (10 mm ×10 mm2 square channel and 2.68 mm×38 mm2 rectangular channel) in such a way that, the mass flow ratio in both the case remain the same (4.9%) in order to compare the effect of bypass channel dimension in the resulting thrust vector angle and thrust performance. Reynolds-averaged Navier-Stokes (RANS) equations with k-omega SST turbulence model have been implemented through numerical computations to capture the three-dimensional steady characterstics of the flow field. Results showed a significant change in the shock structure with the fromation of recirculation zone near the bypass injection port in both the case with a variation of shock structure and thrust performance for different geometry bypass lines. It was found that, thrust vector angle increases as injection length increases in the span wise direction.

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Ruhland, Johannes, and Christian Breitsamter. "Numerical analysis of high-lift configurations with oscillating flaps." CEAS Aeronautical Journal 12, no. 2 (April 2021): 345–59. http://dx.doi.org/10.1007/s13272-021-00498-7.

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AbstractThis study presents two-dimensional aerodynamic investigations of various high-lift configuration settings concerning the deflection angles of droop nose, spoiler and flap in the context of enhancing the high-lift performance by dynamic flap movement. The investigations highlight the impact of a periodically oscillating trailing edge flap on lift, drag and flow separation of the high-lift configuration by numerical simulations. The computations are conducted with regard to the variation of the parameters reduced frequency and the position of the rotational axis. The numerical flow simulations are conducted on a block-structured grid using Reynolds Averaged Navier Stokes simulations employing the shear stress transport $$k-\omega $$ k - ω turbulence model. The feature Dynamic Mesh Motion implements the motion of the oscillating flap. Regarding low-speed wind tunnel testing for a Reynolds number of $$0.5 \times 10^{6}$$ 0.5 × 10 6 the flap movement around a dropped hinge point, which is located outside the flap, offers benefits with regard to additional lift and delayed flow separation at the flap compared to a flap movement around a hinge point, which is located at 15 % of the flap chord length. Flow separation can be suppressed beyond the maximum static flap deflection angle. By means of an oscillating flap around the dropped hinge point, it is possible to reattach a separated flow at the flap and to keep it attached further on. For a Reynolds number of $$20 \times 10^6$$ 20 × 10 6 , reflecting full scale flight conditions, additional lift is generated for both rotational axis positions.

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Zou, Jin, Guoge Tan, Hanbing Sun, Jie Xu, and Yongkang Hou. "Numerical Simulation of the Ducted Propeller and Application to a Semi-Submerged Vehicle." Polish Maritime Research 27, no. 2 (June 1, 2020): 19–29. http://dx.doi.org/10.2478/pomr-2020-0023.

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AbstractThe self-propulsion test of underwater vehicles is the key technique for predicting and evaluating the navigation performance of these submersibles. In this study, the numerical simulation of a standard propeller JD7704+Ka4-70 is first presented and the results are compared with experiments to validate the numerical approaches. The reason why the propulsion efficiency of the ducted propeller is higher than that of the conventional propeller is explored. Then, the paper proposes a series of numerical simulations conducted to test the performance of the ducted propeller designed according to the JD7704+Ka4-70 in order to match with the unmanned semi-submerged vehicle (USSV), and the propeller’s open water characteristic curves are obtained. The results show a reasonable agreement with the regression analysis. Afterwards, the numerical simulations focus on a self-propulsion test of the USSV with the designed ducted propeller and the self-propulsion point is obtained. The streamlines through the hull as well as the ducted propellers are clearly obtained, together with the velocity distributions of the propeller plane. The results vividly demonstrate the hydrodynamic performance of the USSV with the designed propellers. In this paper, all the CFD simulations are based on the numerical software, Star-CCM+, and use the Reynolds-averaged Navier‒Stokes (RANS) equations with the shear stress transport (SST) k-omega turbulence model.

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Bhide, Kalyani, Kiran Siddappaji, and Shaaban Abdallah. "Aspect Ratio Driven Relationship between Nozzle Internal Flow and Supersonic Jet Mixing." Aerospace 8, no. 3 (March 16, 2021): 78. http://dx.doi.org/10.3390/aerospace8030078.

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This work attempts to connect internal flow to the exit flow and supersonic jet mixing in rectangular nozzles with low to high aspect ratios (AR). A series of low and high aspect ratio rectangular nozzles (design Mach number = 1.5) with sharp throats are numerically investigated using steady state Reynolds-averaged Navier−Stokes (RANS) computational fluid dynamics (CFD) with k-omega shear stress transport (SST) turbulence model. The numerical shadowgraph reveals stronger shocks at low ARs which become weaker with increasing AR due to less flow turning at the throat. Stronger shocks cause more aggressive gradients in the boundary layer resulting in higher wall shear stresses at the throat for low ARs. The boundary layer becomes thick at low ARs creating more aerodynamic blockage. The boundary layer exiting the nozzle transforms into a shear layer and grows thicker in the high AR nozzle with a smaller potential core length. The variation in the boundary layer growth on the minor and major axis is explained and its growth downstream the throat has a significant role in nozzle exit flow characteristics. The loss mechanism throughout the flow is shown as the entropy generated due to viscous dissipation and accounts for supersonic jet mixing. Axis switching phenomenon is also addressed by analyzing the streamwise vorticity fields at various locations downstream from the nozzle exit.

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Mahomed, Irshaad, and Beric W. Skews. "Expansion wave diffraction over a 90 degree corner." Journal of Fluid Mechanics 757 (September 25, 2014): 649–64. http://dx.doi.org/10.1017/jfm.2014.491.

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AbstractThe diffraction of an initially one-dimensional plane expansion wave over a 90° corner was explored using experiment and numerical simulation. Unlike studies of shock diffraction, expansion wave diffraction has hardly been documented previously. The planar expansion wave was produced in a shock tube by bursting a diaphragm. Two independent parameters were identified for study: (i) the initial diaphragm shock tube pressure ratio, which determines the strength (pressure ratio) of the expansion, and (ii) the position of the diaphragm from the apex of the 90° corner, which determines the width of the wave. The experimentation only considered variation in the shock tube pressure ratio whereas the simulation varied both parameters. A Navier–Stokes solver with Menter’s shear stress transport $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}k\mbox{--}\omega $ turbulence model was found to adequately model the overall flow field. A number of major flow features were identified occurring in the vicinity of the corner. These were: a shear layer that originated by flow separation at the apex of the corner; a vortex within a separation bubble that remained attached to the wall, in sharp contrast to what happens in the shock wave diffraction case, where the vortex convects downstream; and a reflected compression wave arising from perturbation signals generated by the diffraction. For a narrow-width expansion wave existing prior to diffraction, the reflected compression wave steepens into an outwardly propagating, weak cylindrical shock wave. Regions of supersonic flow are identified surrounding the bubble and can extend downstream depending on the pressure ratio. Another major flow feature identified in some cases was an oblique shock located near the separation bubble. A large wake region is evident immediately downstream of the bubble and appears to consist of two distinct layers. The experimental results showed large-scale turbulent structures within the separation bubble, and shear layer instability and vortex shedding from the separation bubble were also evident.

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Journal articles on the topic 'K-omega turbulence model'

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