Measurement of streamwise vorticity fluctuations in a turbulent channel flow

1983 ◽  
Vol 137 ◽  
pp. 165-186 ◽  
Author(s):  
Elefterios G. Kastrinakis ◽  
Helmut Eckelmann
Keyword(s):  
Channel Flow ◽  
Flow Region ◽  
Turbulent Channel Flow ◽  
Statistical Properties ◽  
Streamwise Vorticity ◽  
Calibration Technique ◽  
Flow Measurements ◽  
Outer Flow ◽  
Hot Wires ◽  
Flatness Factor

In a fully developed turbulent channel flow, measurements of the streamwise vorticity fluctuations ωx have been made. A newly designed probe provides simultaneously in addition to the vorticity signal all three velocity signals. The new probe bears a likeness to the Kovasznay-type vorticity probe, but consists of four electrically independent hot wires, each mounted separately on a total of eight supporting prongs. A new calibration technique had to be developed for this probe.In addition to various statistical properties of the three velocity components, the distributions of vorticity fluctuations and of skewness and flatness factors are given up to wall distances as close as y+ = 19. A pronounced maximum of the streamwise vorticity fluctuations was found at y+ ≈ 20. Large values of the flatness factor characterize the outer flow region.

Small-scale anisotropy in turbulent boundary layers

2016 ◽  
Vol 804 ◽  
pp. 5-23 ◽  
Author(s):  
Alain Pumir ◽  
Haitao Xu ◽  
Eric D. Siggia
Keyword(s):  
Reynolds Number ◽  
Channel Flow ◽  
Isotropic Turbulence ◽  
Turbulent Channel Flow ◽  
Statistical Properties ◽  
Simultaneous Action ◽  
Large Reynolds Number ◽  
Small Scale ◽  
Velocity Fluctuations ◽  
Scale Properties

In a channel flow, the velocity fluctuations are inhomogeneous and anisotropic. Yet, the small-scale properties of the flow are expected to behave in an isotropic manner in the very-large-Reynolds-number limit. We consider the statistical properties of small-scale velocity fluctuations in a turbulent channel flow at moderately high Reynolds number ($Re_{\unicode[STIX]{x1D70F}}\approx 1000$), using the Johns Hopkins University Turbulence Database. Away from the wall, in the logarithmic layer, the skewness of the normal derivative of the streamwise velocity fluctuation is approximately constant, of order 1, while the Reynolds number based on the Taylor scale is $R_{\unicode[STIX]{x1D706}}\approx 150$. This defines a small-scale anisotropy that is stronger than in turbulent homogeneous shear flows at comparable values of $R_{\unicode[STIX]{x1D706}}$. In contrast, the vorticity–strain correlations that characterize homogeneous isotropic turbulence are nearly unchanged in channel flow even though they do vary with distance from the wall with an exponent that can be inferred from the local dissipation. Our results demonstrate that the statistical properties of the fluctuating velocity gradient in turbulent channel flow are characterized, on one hand, by observables that are insensitive to the anisotropy, and behave as in homogeneous isotropic flows, and on the other hand by quantities that are much more sensitive to the anisotropy. How this seemingly contradictory situation emerges from the simultaneous action of the flux of energy to small scales and the transport of momentum away from the wall remains to be elucidated.

Characteristics of Low-Speed Streaks and Vortex Structures in Drag-Reduced Turbulent Channel Flow Investigated by Stereoscopic PIV

2004 ◽  
Author(s):  
Feng-Chen Li ◽  
Yasuo Kawaguchi ◽  
Takehiko Segawa ◽  
Koichi Hishida
Keyword(s):  
Water Flow ◽  
Channel Flow ◽  
Water System ◽  
Turbulent Channel Flow ◽  
Stereoscopic Particle Image Velocimetry ◽  
Streamwise Vorticity ◽  
Solution Flow ◽  
Low Speed ◽  
Turbulence Structures ◽  
Low Speed Streaks

In the present study, we employed stereoscopic particle image velocimetry (SPIV) to investigate the characteristics of turbulence structures in a drag-reduced turbulent channel flow with addition of surfactant. The tested drag-reducing fluid was a CTAC (cetyltrimethyl ammonium chloride)/NaSal/Water system maintained at 25°C, having a 30-ppm concentration of CTAC. SPIV measurement was performed for a water flow (Re=1.1×105) and a CTAC solution flow (RE=1.5×105 with 54% drag reduction) in both the streamwise-spanwise and wall-normal-spanwise planes, respectively. A series of wall-normal vortex cores were found to align with the low-speed streaks with opposite vorticity signals at both sides of the streaks and with the vorticity decreased averagely by about one order in CTAC solution flow compared with water flow; the spanwise spacing between the low-speed streaks in the solution flow is increased by about 42%. The streamwise vorticity of the vortex cores appearing in the wall-normal-spanwise plane was also decreased by the use of additives.

Effects on Topology of a Turbulent Channel Flow Subject to Blowing Through a Porous Strip

2006 ◽  
Author(s):  
L. Labraga ◽  
L. Keirsbulck ◽  
M. Haddad ◽  
M. Elhassan
Keyword(s):  
Channel Flow ◽  
Momentum Flux ◽  
Turbulent Channel Flow ◽  
Time Correlation ◽  
Skin Friction Coefficient ◽  
Wall Region ◽  
Reynolds Stresses ◽  
Hot Wire ◽  
Flow Measurements ◽  
Porous Strip

An experimental investigation is performed on a fully developed turbulent channel flow with local injection through a porous strip. The Reynolds number based on the channel half-width was set to 5000. In addition to the no blowing data, measurements are made for three different blowing rates σ = 0.22, 0.36 and 0.58 (where σ is the ratio of momentum flux gain due to the blowing and momentum flux of the incoming channel flow). Measurements carried out with hot-wire anemometry reveal that injection strongly affects both the velocity profiles and the turbulence characteristics. The injection decreases the skin friction coefficient and increases all the Reynolds stresses downstream the blowing strip. Moreover, the anisotropic invariant map (A.I.M.) for the Reynolds stress tensor revealed that blowing decreased the anisotropy of the turbulent structure in the near wall region and a decrease in the longitudinal integral length scale was observed when the blowing rate increased. The space time correlation measurements show that injection increases the inclination of the coherent structures in both (x,y) and (x,z) plan.

Sign in / Sign up

Export Citation Format

Share Document