An Experimental Investigation in a Turbulent Channel Flow With a Thick Viscous Sublayer (Hot-Film Measurements in Oil)

In a turbulent channel-flow hot-film measurements have been made. To achieve a sublayer thickness of approximately 1 cm at y+ = 10, oil was used. The Reynolds numbers used for the investigations were 5,600 and 8,200 based on the channel-width of 22 cm and the channel center-line velocity. In the vicinity of the wall, y+ \u3c 0.1, the u\u27-fluctuations were found to be proportional to the wall distance, y+. The u\u27-values obtained with a hot-film probe for y+ \u3e 0.7 were all greater than those obtained with a hot-film wall probe, but extrapolation of the data from the movable hot-film probe to the wall gave good agreement with the data from the flush-mounted wall-film probe. The instantaneous values of the u\u27-fluctuations in the region 0 \u3c y+ \u3c 5 are very similar to the instantaneous values of the wall-gradient, but there is a time shift which is proportional to the wall distance, y+. Disturbances in the flow in this region were observed to be convected with a constant velocity toward the wall. The mean value of the convection velocity was found to be approximately equal to the friction velocity, uT. The Reynolds stress was found to be intermittent in the vicinity of the wall with high peak to mean ratios. It was found that the probability density of the instantaneous streamwise velocity is skewed for all y+ values except y+ ≈ 13. For y+ \u3c 13 the most probable instantaneous velocity is less than the mean velocity; for y+ \u3e 13 the opposite was found

Investigation of near wall Turbulence using Multiplane Stereo PIV

The joint probability density functions of the streamwise/wall-normal (uv) and streamwise/spanwise (uw) velocity fluctuations undergo a strong structual change in the near wall region of a fully developed turbulent boundary layer flow when approaching the wall. In order to understand the physics behind this experimental result, the spatio-temporal flow structure was investigated at several y locations, both simultaneously and separated in time, by means of multiplane stereo PIV. The size, shape and intensity of various coherent velocity structures could be determined from the spatio-temporal cross correlation functions after subdividing the flow field according to the quadrand splitting technique. Furthermore the convection velocity of the different coherent structures was measure

Steuerung der Vorderkantenablösung an einem Tragflügel mittels interner Schallanregung

Durch künstlich erzeugte periodische Durchströmung eines Schlitzes nahe der Profilvorderkante eines NACA 0012-Tragflügelprofils konnte eine vollständig abgelöste Strömung oberhalb des kritischen Anstellwinkels wieder zum Anlegen gebracht werden. Dabei erwiesen sich drei Frequenzbereiche als besonders effektiv, in denen sich das Wiederanlegen der abgelösten Strömung durch Anregung der freien Scherschicht mit besonders geringen Anregungspegeln erreichen ließ. Ein weiteres wichtiges Ergebnis war, daß im Bereich höherer Reynoldszahlen bei geeigneten Abmessungen der Kombination aus Schlitzen und darunterliegendem abgeschlossenen zylindrischen Hohlraum selbsterregte Resonanzschwingungen auftraten, die eine dynamische Beeinflussung der Strömungsablösung ohne externe Energiezufuhr ermöglichten

Base Bleed Efficiency Criterion

The base bleed of a two-dimensional body with different slot widths at the trailing edge is examined. It is shown that the value of the maximum base pressure depends on the slot width but in all cases corresponds to the same value of the momentum flux density. This parameter is determined only by the body drag. Turbulent characteristics of the wake behind the body are measured at the optimum value of the momentum flux density. Visualization of the flowpattern immediately behind the trailing edge of the body was made without and with bleeding

The effect of jet bleed on base pressure distribution, shedding frequency, and mean velocity profiles in the wake behind a two-dimensional blunt model

SIGLEAvailable from TIB Hannover: RA 1396(1990,9) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

An experimental investigation of base bleed effect on the wake turbulent structure behind of two-dimensional blunt model

SIGLEAvailable from TIB Hannover: RA 1396(1991,9) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman