Aero-Optical Effects of Mc=0.5 Supersonic Mixing Layer

2014 ◽  
Vol 989-994 ◽  
pp. 863-866
Author(s):  
Li Feng Tian ◽  
Shi He Yi ◽  
Yang Zhu Zhu ◽  
Yu Xin Zhao ◽  
Lin He
Keyword(s):  
Large Scale ◽  
Near Field ◽  
Mixing Layer ◽  
Wavefront Aberration ◽  
Spatiotemporal Resolution ◽  
Large Scale Structures ◽  
Supersonic Mixing ◽  
Optical Effects ◽  
Supersonic Mixing Layer ◽  
Scale Structures

Supersonic turbulent mixing layer requires high spatiotemporal resolution of measuring techniques to study its aero-optical effects. However, the spatiotemporal resolution of existing techniques is not high enough. NPLS-WT (NPLS based wavefront technique) is a new aero-optics measuring technique developed in 2010. Its time resolution is 6ns, and spatial resolution and time correction resolution can reach up to micrometers and 200ns respectively. NPLS-WT was used in this paper to study aero-optical effects induced by Mc=0.5 supersonic mixing layer. The fine wavefront aberration information is revealed by the OPD of high resolution. The results show that the wavefront in near field is not sensitive to the resolution, and large-scale structures play a dominant role on the wavefront in near field. The cumulative effects analysis show us that the density difference between large-scale structures and free stream is the main reason to wavefront aberration, and the larger the vortex is, the more obvious the effect to wavefront aberration is.

scholarly journals Characteristics of Large-Scale Structures in Supersonic Planar Mixing Layer with Finite Thickness

2014 ◽  
Vol 6 ◽  
pp. 878679
Author(s):  
Hailong Zhang ◽  
Jiping Wu ◽  
Jian Chen ◽  
Weidong Liu
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Finite Thickness ◽  
Mixing Layer ◽  
Mixing Enhancement ◽  
Laser Scattering ◽  
Large Scale Structures ◽  
Eddy Simulation ◽  
Planar Laser ◽  
Scale Structures

Nanoparticle-based planar laser scattering (NPLS) experiments and large eddy simulation (LES) were launched to get the fine structure of the supersonic planar mixing layer with finite thickness in the present study. Different from the turbulent development of supersonic planar mixing layer with thin thickness, the development of supersonic planar mixing layer with finite thickness is rapidly. The large-scale structures of mixing layer that possess the characters of quick movement and slow changes transmit to downriver at invariable speed. The transverse results show that the mixing layer is strip of right and dim and possess 3D characteristics. Meanwhile the vortices roll up from two sides to the center. Results indicate that the higher the pressure of the high speed side is, the thicker the mixing layer is. The development of mixing layer is restrained when the pressure of lower speed side is higher. The momentum thickness goes higher with the increase of the clapboard thickness. Through increasing the temperature to change the compression can affect the development of the vortices. The present study can make a contribution to the mixing enhancement and provide initial data for the later investigations.

scholarly journals Examination of large-scale structures in a turbulent plane mixing layer. Part 2. Dynamical systems model

2001 ◽  
Vol 441 ◽  
pp. 67-108 ◽  
Author(s):  
L. UKEILEY ◽  
L. CORDIER ◽  
R. MANCEAU ◽  
J. DELVILLE ◽  
M. GLAUSER ◽  
...  
Keyword(s):  
Dynamical System ◽  
Velocity Field ◽  
Large Scale ◽  
Stokes Equations ◽  
Temporal Dynamics ◽  
Mixing Layer ◽  
Basis Set ◽  
Large Scale Structures ◽  
Scale Structures ◽  
Low Order

The temporal dynamics of large-scale structures in a plane turbulent mixing layer are studied through the development of a low-order dynamical system of ordinary differential equations (ODEs). This model is derived by projecting Navier–Stokes equations onto an empirical basis set from the proper orthogonal decomposition (POD) using a Galerkin method. To obtain this low-dimensional set of equations, a truncation is performed that only includes the first POD mode for selected streamwise/spanwise (k1/k3) modes. The initial truncations are for k3 = 0; however, once these truncations are evaluated, non-zero spanwise wavenumbers are added. These truncated systems of equations are then examined in the pseudo-Fourier space in which they are solved and by reconstructing the velocity field. Two different methods for closing the mean streamwise velocity are evaluated that show the importance of introducing, into the low-order dynamical system, a term allowing feedback between the turbulent and mean flows. The results of the numerical simulations show a strongly periodic flow indicative of the spanwise vorticity. The simulated flow had the correct energy distributions in the cross-stream direction. These models also indicated that the events associated with the centre of the mixing layer lead the temporal dynamics. For truncations involving both spanwise and streamwise wavenumbers, the reconstructed velocity field exhibits the main spanwise and streamwise vortical structures known to exist in this flow. The streamwise aligned vorticity is shown to connect spanwise vortex tubes.

scholarly journals Large-Scale Structures in a Subsonic Mixing Layer

1994 ◽  
Vol 6 (9) ◽  
pp. S7-S7 ◽  
Author(s):  
Saad Ragab ◽  
Madhu Sreedhar ◽  
Daniel Mulholland
Keyword(s):  
Large Scale ◽  
Mixing Layer ◽  
Large Scale Structures ◽  
Scale Structures

scholarly journals A LES Study on Passive Mixing in Supersonic Shear Layer Flows Considering Effects of Baffle Configuration

2014 ◽  
Vol 6 ◽  
pp. 836146 ◽  
Author(s):  
Ren Zhao-Xin ◽  
Wang Bing
Keyword(s):  
Pressure Loss ◽  
Total Pressure ◽  
Large Scale ◽  
Mixing Layer ◽  
Total Pressure Loss ◽  
Mixing Efficiency ◽  
Mixing Enhancement ◽  
Supersonic Mixing ◽  
Passive Mixing ◽  
Supersonic Mixing Layer

Under the background of dual combustor ramjet (DCR), a numerical investigation of supersonic mixing layer was launched, focused on the mixing enhancement method of applying baffles with different geometric configurations. Large eddy simulation with high order schemes, containing a fifth-order hybrid WENO compact scheme for the convective flux and sixth-order compact one for the viscous flux, was utilized to numerically study the development of the supersonic mixing layer. The supersonic cavity flow was simulated and the cavity configuration could influence the mixing characteristics, since the impingement process of large scale structures formed inside the cavity could raise the vorticity and promote the mixing. The effect of baffle's configurations on the mixing process was analyzed by comparing the flow properties, mixing efficiency, and total pressure loss. The baffle could induce large scale vortexes, promote the mixing layer to lose its stability easily, and then lead to the mixing efficiency enhancement. However, the baffle could increase the total pressure loss. The present investigation could provide guidance for applying new passive mixing enhancement methods for the supersonic mixing.

Dynamics of Large-Scale Structures for Jets in a Crossflow

1999 ◽  
Vol 121 (3) ◽  
pp. 577-587 ◽  
Author(s):  
F. Muldoon ◽  
S. Acharya
Keyword(s):  
Shear Layer ◽  
Large Scale ◽  
Computational Study ◽  
Near Field ◽  
Velocity Ratio ◽  
Leeward Side ◽  
Dynamic Features ◽  
Mean Velocity ◽  
Large Scale Structures ◽  
Scale Structures

Results of a three-dimensional unsteady computational study of a row of jets injected normal to a crossflow are presented with the aim of understanding the dynamics of the large-scale structures in the region near the jet. The jet to crossflow velocity ratio is 0.5. A modified version of the computer program (INS3D), which utilizes the method of artificial compressibility, is used for the computations. Results obtained clearly indicate that the near-field large-scale structures are extremely dynamic in nature, and undergo breakup and reconnection processes. The dynamic near-field structures identified include the counterrotating vortex pair (CVP), the horseshoe vortex, wake vortex, wall vortex, and shear layer vortex. The dynamic features of these vortices are presented in this paper. The CVP is observed to be a convoluted structure interacting with the wall and horseshoe vortices. The shear layer vortices are stripped by the crossflow, and undergo pairing and stretching events in the leeward side of the jet. The wall vortex is reoriented into the upright wake system. Comparison of the predictions with mean velocity measurements is made. Reasonable agreement is observed.

Large-scale structures in a forced turbulent mixing layer

1985 ◽  
Vol 150 ◽  
pp. 23-39 ◽  
Author(s):  
M. Gaster ◽  
E. Kit ◽  
I. Wygnanski
Keyword(s):  
Turbulent Mixing ◽  
Large Scale ◽  
Phase Distribution ◽  
Mixing Layer ◽  
Global Scale ◽  
Travelling Wave ◽  
Mean Flow ◽  
Turbulent Mixing Layer ◽  
Large Scale Structures ◽  
Scale Structures

The large-scale structures that occur in a forced turbulent mixing layer at moderately high Reynolds numbers have been modelled by linear inviscid stability theory incorporating first-order corrections for slow spatial variations of the mean flow. The perturbation stream function for a spatially growing time-periodic travelling wave has been numerically evaluated for the measured linearly diverging mean flow. In an accompanying experiment periodic oscillations were imposed on the turbulent mixing layer by the motion of a small flap at the trailing edge of the splitter plate that separated the two uniform streams of different velocity. The results of the numerical computations are compared with experimental measurements.When the comparison between experimental data and the computational model was made on a purely local basis, agreement in both the amplitude and phase distribution across the mixing layer was excellent. Comparisons on a global scale revealed, not unexpectedly, less good accuracy in predicting the overall amplification.

Vortex dynamics and sound emission in excited high-speed jets

2018 ◽  
Vol 839 ◽  
pp. 313-347 ◽  
Author(s):  
Michael Crawley ◽  
Lior Gefen ◽  
Ching-Wen Kuo ◽  
Mo Samimy ◽  
Roberto Camussi
Keyword(s):  
Shear Layer ◽  
Large Scale ◽  
Noise Source ◽  
Near Field ◽  
Velocity Fields ◽  
Source Mechanism ◽  
Time Resolved ◽  
Large Scale Structures ◽  
Coherent Ring ◽  
Scale Structures

This work aims to study the dynamics of and noise generated by large-scale structures in a Mach 0.9 turbulent jet of Reynolds number $6.2\times 10^{5}$ using plasma-based excitation of shear layer instabilities. The excitation frequency is varied to produce individual or periodic coherent ring vortices in the shear layer. First, two-point cross-correlations are used between the acoustic near field and far field in order to identify the dominant noise source region. The large-scale structure interactions are then investigated by stochastically estimating time-resolved velocity fields using time-resolved near-field pressure traces and non-time-resolved planar velocity snapshots (obtained by particle image velocimetry) by means of an artificial neural network. The estimated time-resolved velocity fields show multiple mergings of large-scale structures in the shear layer, and indicate that disintegration of coherent ring vortices is the dominant aeroacoustic source mechanism for the jet studied here. However, the merging of vortices in the initial shear layer is also identified as a non-trivial noise source mechanism.

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