scholarly journals Implicit LES for Supersonic Microramp Vortex Generator: New Discoveries and New Mechanisms

2011 ◽  
Vol 2011 ◽  
pp. 1-15 ◽  
Author(s):  
Qin Li ◽  
Chaoqun Liu
Keyword(s):  
Vortex Ring ◽  
Vortex Tube ◽  
Vortex Generator ◽  
Shock Interaction ◽  
Surface Separation ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Boundary Layer Interaction ◽  
Fifth Order ◽  
Made In

This paper serves as a summary of our recent work on LES for supersonic MVG. An implicitly implemented large eddy simulation (ILES) by using the fifth-orderWENOscheme is applied to study the flow around the microramp vortex generator (MVG) at Mach 2.5 andRe⁡θ=1440. A number of new discoveries on the flow around supersonic MVG have been made including spiral points, surface separation topology, source of the momentum deficit, inflection surface, Kelvin-Helmholtz instability, vortex ring generation, ring-shock interaction, 3D recompression shock structure, and influence of MVG decline angles. Most of the new discoveries, which were made in 2009, were confirmed by experiment conducted by the UTA experimental team in 2010. A new 5-pair-vortex-tube model near the MVG is given based on the ILES observation. The vortex ring-shock interaction is found as the new mechanism of the reduction of the separation zone induced by the shock-boundary layer interaction.

Flow Around a Simplified Car, Part 1: Large Eddy Simulation

2005 ◽  
Vol 127 (5) ◽  
pp. 907-918 ◽  
Author(s):  
Siniša Krajnović ◽  
Lars Davidson
Keyword(s):  
Reynolds Number ◽  
The Body ◽  
Ground Vehicle ◽  
Surface Separation ◽  
Recirculating Flow ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Reynolds Number Effects ◽  
Sharp Edges ◽  
High Reynolds

Large eddy simulations (LES) were made of flows around a generic ground vehicle with sharp edges at the rear end (an Ahmed body with a 25° angle of the rear slanted surface). Separation of the flow at the rear results in large regions with recirculating flow. As the separation is determined by the geometry, the Reynolds number effects are minimized. Resolution requirements of this recirculating flow are smaller than those in LES of wall attached flows. These two consequences of the geometry of the body are used to predict the experimental flow at relatively high Reynolds number. Recommendations are presented for the preparation and realization of LES for vehicle flows. Comparison of the LES results with the experimental data shows good agreement.

Large-Eddy Simulation and Passive Control of Flows for a Low Pressure Turbine Cascade

2009 ◽  
Author(s):  
Jibing Lan ◽  
Yonghui Xie ◽  
Di Zhang ◽  
Jing Shu
Keyword(s):  
Pressure Fluctuation ◽  
Passive Control ◽  
Static Pressure ◽  
Separation Bubble ◽  
Suction Surface ◽  
Surface Separation ◽  
Low Pressure Turbine ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Fluctuation Frequency

A rectangular bar which just likes a forward-backward facing step was designed to passive control of the Low-Pressure Turbine (LPT) PakB cascade suction surface separation. Large-eddy simulation (LES) was adopted to analyze the separated-transition flows for the PakB cascade with and without the rectangular bar at Re (Reynolds number based on inlet condition and axial chord) of 86,000 and the freestream turbulence intensity of 1%. Computed results of uncontrolled condition agree well with the experimental data of Lake et al.[6, 7]. And the LES results shown that the rectangular bar control device was successful to control the LPT cascade suction surface separation and provides about 10% kinetic loss coefficient reduction from the uncontrolled one. Unsteady flow structures were also investigated in detail. Static pressure fluctuation frequency at six locations, ranging from 0.56Cx to 0.95Cx axial chord location and with a constant wall normal distance y/h = 1.0, was the same to the separation bubble vortex shedding frequency. Unsteady fluctuation velocity was examined too, which confirmed that the separation bubble vortex frequency was the same to the suction surface static pressure fluctuation frequency.

Large Eddy Simulation of a Vortex Ring Impacting a Bump

2014 ◽  
Vol 6 (3) ◽  
pp. 261-280
Author(s):  
Heng Ren ◽  
Ning Zhao ◽  
Xi-Yun Lu
Keyword(s):  
Large Eddy Simulation ◽  
Vortex Ring ◽  
Three Dimensional ◽  
Vortical Flow ◽  
Flow State ◽  
Vortical Structures ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Flow Phenomena ◽  
Flow Evolution

AbstractA vortex ring impacting a three-dimensional bump is studied using large eddy simulation for a Reynolds number Re = 4 × 104 based on the initial diameter and translational speed of the vortex ring. The effects of bump height and vortex core thickness for thin and thick vortex rings on the vortical flow phenomena and the underlying physical mechanisms are investigated. Based on the analysis of the evolution of vortical structures, two typical kinds of vortical structures, i.e., the wrapping vortices and the hair-pin vortices, are identified and play an important role in the flow state evolution. The boundary vorticity flux is analyzed to reveal the mechanism of the vorticity generation on the bump surface. The circulation of the primary vortex ring reasonably elucidates some typical phases of flow evolution. Further, the analysis of turbulent kinetic energy reveals the transition from laminar to turbulent state. The results obtained in this study provide physical insight into the understanding of the mechanisms relevant to the flow evolution and the flow transition to turbulent state.

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