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The effect of three different sized transverse square grooves (5, 10, and 20 mm) on a turbulent boundary layer was investigated at two values of momentum thickness Reynolds numbers (Rθ=1,000 and 3,000) using hot-wire anemometry. The ratios of the groove depth to the boundary layer thickness (d/δ0) are approximately 0.07, 0.13, and 0.27. Wall shear stress (τw), mean velocity (U), and turbulence intensity downstream of the grooves are compared to those on a corresponding smooth wall The effects of the grooves are more significant at the higher Rθ, with the most pronounced effects caused by the largest size groove. There is an increase in mean velocity (U), streamwise (u′/U0), and wall-normal (ν′/U0) turbulence intensities in the near-wall region immediately downstream of the grooves. The increase propagates outwards in the layer as the streamwise distance increases downstream of the grooves. The increase in ν′/U0is much more significant than that of u′/U0, which is also evident in the spectra of u′ and ν′. There is an increase in τwover the smooth wall value immediately downstream of the grooves at Rθ=1,000, with the increase being more pronounced as the groove size increases. The growth of the internal layer downstream of the grooves is found to scale with the groove size, and is more rapid at Rθ=3,000.

Abstract: A dual-probe hot-film anemometry technique has been developed to measure multiple gas-bubble velocities corresponding to different gas-bubble size groups in air–water flows. A data reduction scheme using wavelet analysis combined with a phase-detection technique is used to discriminate the hot-film anemometer output signals into signals corresponding to different bubble size groups. The phase and bubble size discrimination is based on the magnitude and time derivative of the signal, and the streamwise length of the gas bubbles. A cross-correlation between the discriminated signals from the two probes yields an average time difference of arrival of the gas bubbles at the two sensor locations. The velocities are estimated from the distance between the sensors and the time difference of arrival. The mean bubble size is estimated from the chord length distribution. Measurements performed in vertical-up air–water slug flow show the technique to be a viable method for obtaining bubble velocity and size information. The velocity measurements from the hot-film anemometry are corroborated using a high-speed quantitative flow visualization system.

Laser-Doppler velocimetry (LDV) measurements and flow visualizations are used to study a turbulent boundary layer over a smooth wall with transverse square cavities at two values of the momentum thickness Reynolds number (R?=400 and 1300). The cavities are spaced 20 element widths apart in the streamwise direction. Flow visualizations reveal a significant communication between the cavities and the overlying shear layer, with frequent inflows and ejections of fluid to and from cavities. There is evidence to suggest that quasi-streamwise near-wall vortices are responsible for the ejections of fluid out of the cavities. The wall shear stress, which is measured accurately, increases sharply immediately downstream of the cavity. This increase is followed by a sudden decrease and a slower return to the smooth wall value. Integration of the wall shear stress in the streamwise direction indicates that there is an increase in drag of 3.4% at bothR?.

Low-Reynolds-number effects in a zero pressure gradient turbulent boundary layer have been investigated using a two-component LDV system. The momentum thickness Reynolds number R? is in the range 400 to 1320. The wall shear stress is determined from the mean velocity gradient close to the wall, allowing scaling on wall variables of the inner region of the layer to be examined unambiguously. The results indicate that, for the present R? range, this scaling is not appropriate. The effect of R? on the Reynolds normal and shear stresses is felt within the sublayer. Outside the buffer layer, the mean velocity is more satisfactorily described by a power-law than by a logarithmic distribution.

This experiment investigated the effects of free-stream turbulence intensity, length scale, Reynolds number, and leading-edge velocity gradient on stagnation-region heat transfer. Heat transfer was measured in the stagnation region of four models with elliptical leading edges downstream of five turbulence-generating grids. Stagnation-region heat transfer augmentation increased with decreasing length scale but ann optimum scale was not found. A correlation was developed that fit heat transfer data for isotropic turbulence to within ±4 percent but did not predict data for anisotropic turbulence. Stagnation heat transfer augmentation caused by turbulence was unaffected by the velocity gradient. The data of other researchers compared well with the correlation. A method of predicting heat transfer downstream of the stagnation point was developed.

This experiment investigated the effects of free-stream turbulence intensity, length scale, Reynolds number, and leading-edge velocity gradient on stagnation-region heat transfer. Heat transfer was measured in the stagnation region of four models with elliptical leading edges downstream of five turbulence-generating grids. Stagnation-region heat transfer augmentation increased with decreasing length scale but ann optimum scale was not found. A correlation was developed that fit heat transfer data for isotropic turbulence to within ±4 percent but did not predict data for anisotropic turbulence. Stagnation heat transfer augmentation caused by turbulence was unaffected by the velocity gradient. The data of other researchers compared well with the correlation. A method of predicting heat transfer downstream of the stagnation point was developed.

Abstract:  The effect of transverse square grooves on the drag characteristics of a flat plate has been investigated using direct drag measurements in a tow tank. Two flat plates with 2.5 and 5 mm transverse square grooves, with groove spacing (s) to groove width (w) ratio, s/w=10, 20 and 40, were tested at plate length Reynolds numbers in the range 2–10106. There is an increase in drag over the “smooth” plate for all s/w configurations.

The feasibility of using a rotating heat pipe to anti-ice the nose cones of small turbofan aero-engines is investigated. A stationary jacket evaporator design was used to transport heat into the rotating heat pipe located along the central fan shaft of the engine. The rotating heat pipe condenser was made an integral part of the nose cone using a high conductivity, lightweight material and the tip of the nose cone. The use of heating channels along the nose cone and passive heat transfer enhancement in the evaporator were also investigated. The computational model used to predict the heat transfer performance is outlined. The overall heat transfer to the nose cone was 0.8–1.2 kW using water in the heat pipe and 0.4–0.75kW using ethanol. The heating channels were not effective due to the small contact area with the nose cone. The heat transfer enhancement in the evaporator increased the total heat transfer modestly and the temperature of the nose cone increased over the contact area made with the high conductivity material. The results show that rotating heat pipes are a feasible nose cone anti-icing technology.

Natural killer cells capable of lysing herpes simplex virus type 1(HSV-I)-infected fibroblasts were studied in three groups of patients unusually susceptible to severe herpesvirus infections. Cord blood was evaluated because of the known susceptibility of neonates to disseminated infections due to herpes simplex virus type 2 at birth. Only 30% of the cord blood specimens tested demonstrated normal lysis of HSV-l-Infected fibroblasts and a normal increment in the lysis of infected over uninfected cells. Five out of six patients with Wiskott-Aldrich syndrome (WAS) also were found to have abnormally low responses by these criteria. The one WAS patient with normal responses had had little difficulty with infections and had survived much longer than usual. Five patients with severe herpesvirus infections and no known primary cellular immunodeficiency had natural killer cell function significantly below normal (P <0.001). These data suggest that natural killer cells probably play an important role in human resistance to herpesvirus infection and that deficiencies of this system may result in unusual susceptibility to herpesvirus infections.