Studies of shock/turbulent shear layer interaction using Large-Eddy Simulation

2010 ◽  
Vol 39 (5) ◽  
pp. 800-819 ◽  
Author(s):  
Franklin Génin ◽  
Suresh Menon
2015 ◽  
Vol 137 (8) ◽  
Author(s):  
Yuchuan Wang ◽  
Lei Tan ◽  
Binbin Wang ◽  
Shuliang Cao ◽  
Baoshan Zhu

Large eddy simulation (LES) approach was used to investigate jumps of primary frequency of shear layer flow over a cavity. Comparisons between computational results and experimental data show that LES is an appropriate approach to accurately capturing the critical values of velocity and cavity length of a frequency jump, as well as characteristics of the separated shear layer. The drive force of the self-sustained oscillation of impinging shear layer is fluid injection and reinjection. Flow patterns in the shear layer and cavity before and after the frequency jump demonstrate that the frequency jump is associated with vortex–corner interaction. Before frequency jump, a mature vortex structure is observed in shear layer. The vortex is clipped by impinging corner at approximately half of its size, which induces strong vortex–corner interaction. After frequency jump, successive vortices almost escape from impinging corner without the generation of a mature vortex, thereby indicating weaker vortex–corner interaction. Two wave peaks are observed in the shear layer after the frequency jump because of: (1) vortex–corner interaction and (2) centrifugal instability in cavity. Pressure fluctuations inside the cavity are well regulated with respect to time. Peak values of correlation coefficients close to zero time lags indicate the existence of standing waves inside the cavity. Transitions from a linear to a nonlinear process occurs at the same position (i.e., x/H = 0.7) for both velocity and cavity length variations. Slopes of linear region are solely the function of cavity length, thereby showing increased steepness with increased cavity length.


Author(s):  
Souvik Naskar ◽  
S. Sarkar

Abstract Modern commercial airliners use multi-element aerofoils to enhance take-off and landing performance. Further, multielement aerofoil configurations have been shown to improve the aerodynamic characteristics of wind turbines. In the present study, high resolution Large Eddy Simulation (LES) is used to explore the low Reynolds Number (Re = 0.832 × 104) aerodynamics of a 30P30N multi-element aerofoil at an angle of attack, α = 4°. In the present simulation, wake shed from a leading edge element or slat is found to interact with the separated shear layer developing over the suction surface of the main wing. High receptivity of shear layer via amplification of free-stream turbulence leads to rollup and breakdown, forming a large separation bubble. A transient growth of fluctuations is observed in the first half of the separation bubble, where levels of turbulence becomes maximum near the reattachment and then decay depicting saturation of turbulence. Results of the present LES are found to be in close agreement with the experiment depicting high vortical activity in the outer layer. Some features of the flow field here are similar to those occur due to interactions of passing wake and the separated boundary layer on the suction surface of high lift low pressure turbine blades.


2016 ◽  
Vol 139 (1) ◽  
Author(s):  
K. M. Nair ◽  
S. Sarkar

The primary objective is to perform a large eddy simulation (LES) using shear improved Smagorinsky model (SISM) to resolve the large-scale structures, which are primarily responsible for shear layer oscillations and acoustic loads in a cavity. The unsteady, three-dimensional (3D), compressible Navier–Stokes (N–S) equations have been solved following AUSM+-up algorithm in the finite-volume formulation for subsonic and supersonic flows, where the cavity length-to-depth ratio was 3.5 and the Reynolds number based on cavity depth was 42,000. The present LES resolves the formation of shear layer, its rollup resulting in large-scale structures apart from shock–shear layer interactions, and evolution of acoustic waves. It further indicates that hydrodynamic instability, rather than the acoustic waves, is the cause of self-sustained oscillation for subsonic flow, whereas the compressive and acoustic waves dictate the cavity oscillation, and thus the sound pressure level for supersonic flow. The present LES agrees well with the experimental data and is found to be accurate enough in resolving the shear layer growth, compressive wave structures, and radiated acoustic field.


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