scholarly journals Characteristics of vortex packets in turbulent boundary layers

2003 ◽  
Vol 478 ◽  
pp. 35-46 ◽  
Author(s):  
BHARATHRAM GANAPATHISUBRAMANI ◽  
ELLEN K. LONGMIRE ◽  
IVAN MARUSIC
Keyword(s):  
Vector Fields ◽  
Spatial Organization ◽  
Reynolds Shear Stress ◽  
Stereoscopic Particle Image Velocimetry ◽  
Hairpin Vortices ◽  
Image Velocimetry ◽  
Extraction Algorithm ◽  
Logarithmic Layer ◽  
Identification And Characterization

Stereoscopic particle image velocimetry (PIV) was used to measure all three instantaneous components of the velocity field in streamwise–spanwise planes of a turbulent boundary layer at Reτ=1060 (Reθ=2500). Datasets were obtained in the logarithmic layer and beyond. The vector fields in the log layer (z+=92 and 150) revealed signatures of vortex packets similar to those proposed by Adrian and co-workers in their PIV experiments. Groups of legs of hairpin vortices appeared to be coherently arranged in the streamwise direction. These regions also generated substantial Reynolds shear stress, sometimes as high as 40 times −uw. A feature extraction algorithm was developed to automate the identification and characterization of these packets of hairpin vortices. Identified patches contributed 28% to −uw while occupying only 4% of the total area at z+=92. At z+=150, these patches occupied 4.5% of the total area while contributing 25% to −uw. Beyond the log layer (z+=198 and 530), the spatial organization into packets is seen to break down.

Very-large-scale motions in a turbulent boundary layer

2011 ◽  
Vol 673 ◽  
pp. 80-120 ◽  
Author(s):  
JAE HWA LEE ◽  
HYUNG JIN SUNG
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Turbulent Boundary Layer ◽  
Large Scale ◽  
Spatial Organization ◽  
Reynolds Shear Stress ◽  
Three Dimensional ◽  
Hairpin Vortices ◽  
Extraction Algorithm ◽  
Normal Distance

Direct numerical simulation of a turbulent boundary layer was performed to investigate the spatially coherent structures associated with very-large-scale motions (VLSMs). The Reynolds number was varied in the range Reθ = 570–2560. The main simulation was conducted by using a computational box greater than 50δo in the streamwise domain, where δo is the boundary layer thickness at the inlet, and inflow data was obtained from a separate inflow simulation based on Lund's method. Inspection of the three-dimensional instantaneous fields showed that groups of hairpin vortices are coherently arranged in the streamwise direction and that these groups create significantly elongated low- and high-momentum regions with large amounts of Reynolds shear stress. Adjacent packet-type structures combine to form the VLSMs; this formation process is attributed to continuous stretching of the hairpins coupled with lifting-up and backward curling of the vortices. The growth of the spanwise scale of the hairpin packets occurs continuously, so it increases rapidly to double that of the original width of the packets. We employed the modified feature extraction algorithm developed by Ganapathisubramani, Longmire & Marusic (J. Fluid Mech., vol. 478, 2003, p. 35) to identify the properties of the VLSMs of hairpin vortices. In the log layer, patches with the length greater than 3δ–4δ account for more than 40% of all the patches and these VLSMs contribute approximately 45% of the total Reynolds shear stress included in all the patches. The VLSMs have a statistical streamwise coherence of the order of ~6δ; the spatial organization and coherence decrease away from the wall, but the spanwise width increases monotonically with the wall-normal distance. Finally, the application of linear stochastic estimation demonstrated the presence of packet organization in the form of a train of packets in the log layer.

scholarly journals Experimental Investigation of Flow Structures Around side-by-side Yawed Cylinders in Shallow Water

2019 ◽  
Vol 2 (3) ◽  
pp. 1138-1151
Author(s):  
Ebubekir Kütük ◽  
Umutcan Olmuş ◽  
Tahir Durhasan ◽  
Hüseyin Akıllı
Keyword(s):  
Shear Stress ◽  
Shallow Water ◽  
Vector Fields ◽  
Particle Image ◽  
Reynolds Shear Stress ◽  
Flow Structures ◽  
Piv Technique ◽  
Gap Ratio ◽  
Image Velocimetry ◽  
Yaw Angle

The aim of this experimental study is to investigate the flow behaviour around two equally yawed side-by-side cylinders in shallow water. Time averaged velocity vector fields, Reynolds shear stress distrubutions and streamline patterns were obtained using Particle Image Velocimetry (PIV) technique. The gap ratio between the cylinders were in the range of G/D=0.25-1.25 with an increment of 0.25 where G is the distance between the cylinders and D is the cylinder diameter. Five different yaw angles of cylinders were employed during the experiment. The results showed that the yaw angle, α had an important effect on the flow structures of the downstream of the cylinders. Reynolds shear stress and vortex structures were decreased, the intensity of the jet like flow were significantly attenuated for the gap ratios of G/D=0.25, 0.50 and 0.75.

Estimation of Turbulent Length Scales at a Turbocharger Inlet Using Particle Image Velocimetry

2021 ◽  
Author(s):  
Deb Banerjee ◽  
Ahmet Selamet ◽  
Rick Dehner
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Operating Conditions ◽  
Stereoscopic Particle Image Velocimetry ◽  
Length Scales ◽  
Image Velocimetry ◽  
Fundamental Understanding ◽  
Compressor Inlet ◽  
Kolmogorov Scale

Abstract Stereoscopic Particle Image Velocimetry measurements are carried out at the inlet of a turbocharger compressor at four different shaft speeds from 80,000 rpm to 140,000 rpm and over the entire range of flow rates from choke to mild surge. This paper describes the procedure used in processing the PIV data leading to the estimates of turbulent length scales – integral, Taylor, and Kolmogorov, to enhance the fundamental understanding and characterization of the compressor inlet flow field. The analysis reveals that at most operating conditions the three different length scales have markedly different magnitudes, as expected, while they have somewhat similar qualitative distributions with respect to the duct radius. For example, at 80,000 rpm and at a flow rate of 15.7 g/s (mild surge), the longitudinal integral length scale is of the order of 15 mm, the Taylor scale is around 0.5 mm, and the Kolmogorov scale is about 10 microns. With the onset of flow reversal, the turbulent kinetic energy and turbulent intensity at the compressor inlet are observed to increase rapidly, while the magnitudes of the Kolmogorov scale and to a certain extent, the Taylor scale are found to decrease suggesting that the increased turbulence gives rise to even smaller flow structures. The variation of length scales with compressor shaft speed has also been studied.

Estimation of Turbulent Length Scales at a Turbocharger Inlet using Stereoscopic Particle Image Velocimetry

2022 ◽  
Author(s):  
Deb Banerjee ◽  
Ahmet Selamet ◽  
Rick Dehner
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Operating Conditions ◽  
Stereoscopic Particle Image Velocimetry ◽  
Length Scales ◽  
Image Velocimetry ◽  
Fundamental Understanding ◽  
Compressor Inlet ◽  
Kolmogorov Scale

Abstract Stereoscopic Particle Image Velocimetry measurements are carried out at the inlet of a turbocharger compressor at four different shaft speeds from 80,000 rpm to 140,000 rpm and over the entire range of flow rates from choke to mild surge. This paper describes the procedure used in processing the PIV data leading to the estimates of turbulent length scales - integral, Taylor, and Kolmogorov, to enhance the fundamental understanding and characterization of the compressor inlet flow field. The analysis reveals that at most operating conditions the three different length scales have markedly different magnitudes, as expected, while they have somewhat similar qualitative distributions with respect to the duct radius. For example, at 80,000 rpm and at a flow rate of 15.7 g/s (mild surge), the longitudinal integral length scale is of the order of 15 mm, the Taylor scale is around 0.5 mm, and the Kolmogorov scale is about 10 microns. With the onset of flow reversal, the turbulent kinetic energy and turbulent intensity at the compressor inlet are observed to increase rapidly, while the magnitudes of the Kolmogorov scale and to a certain extent, the Taylor scale are found to decrease suggesting that the increased turbulence gives rise to even smaller flow structures. The variation of length scales with compressor shaft speed has also been studied.

Experimental and Computational Characterization of a Large-Scale, Underwater Towed SPIV System

2017 ◽  
Author(s):  
Emily L. Harrison ◽  
Joseph P. Ramsey ◽  
Li Jiang
Keyword(s):  
Large Scale ◽  
Reynolds Numbers ◽  
Stereoscopic Particle Image Velocimetry ◽  
Taylor Model ◽  
Eddy Simulation ◽  
Image Velocimetry ◽  
Large Eddy ◽  
Out Of Plane ◽  
Naval Surface Warfare

A new underwater Stereoscopic Particle Image Velocimetry (SPIV) Torpedo system was designed and constructed at the Naval Surface Warfare Center, Carderock Division for testing in the David Taylor Model Basin. The purpose of the work was to conduct a shakedown test of the new SPIV system to ensure it properly captured SPIV images, and successfully resolved both the in- and out-of-plane velocity fields. To test the system, SPIV measurements were taken on the free-stream flow in the basin and the canonical flow field produced by a circular cylinder at Reynolds numbers around 100,000. After successfully measuring the flow fields, cylinder results were compared to large eddy simulation results that were obtained using NavyFOAM.

Sign in / Sign up

Export Citation Format

Share Document