Traditional Wind Tunnel Research Articles

Debate Concerning the Mean-Velocity Profile of a Turbulent Boundary Layer

There has been considerable controversy during the past few years concerning the validity of the classical log law that describes the overlap region of the mean-velocity profile in the canonical turbulent boundary layer. Alternative power laws have been proposed by Barenblatt, Chorin, George, and Castillo, to name just a few. Advocates of either law typically have used selected data sets to foster their claims. The experimental and direct numerical simulation data sets from six independent groups are analyzed. For the range of momentum-thickness Reynolds numbers of 5£ 10 2 ‐2:732£ 10 4 , the best-fit values are determined for the “constants” appearing in either law. Our strategy involves calculating the fractional difference between the measured/computed mean velocity and that calculated using either of the two respective laws. This fractional difference is bracketed in the region § §0:5%, so that an accurate, objective measure of the boundary and extent of either law is determined. It is found that, although the extent of the power-law region in outer variables is nearly constant over a wide range of Reynolds numbers, the log-region extent increases monotonically with Reynolds number. The log law and the power law do not cover the same portion of the velocity profile. A very small zone directly above the buffer layer is not represented by the power law. On the other hand, the inner region of the wake zone is covered by it. In the region where both laws show comparable fractional differences, the mean and variance were calculated. From both measures, it is concluded that the examined data do not indicate any statistically significant preference toward either law. I. The Opening Arguments T HE Reynolds numbers encountered in many practical situations are typically several orders of magnitude higher than those studied computationally or even experimentally. High-Reynoldsnumber research facilities are expensive to build and operate, and the few existing are heavily scheduled with mostly developmental work. For traditional wind tunnels, additional complications are introduced at high speeds due to compressibility effects and probe-resolution limitations near walls. Likewise, full computational simulation of high-Reynolds-number flows is beyond the reach of current capabilities. Understanding of turbulence and modeling will, therefore, continue to play a vital role in the computation of high Reynolds number practical flows using the Reynolds averaged Navier‐Stokes equations. Because the existing knowledge base, accumulated mostly through physical as well as numerical experiments, is skewed toward the low Reynolds numbers, the key question in modeling high-Reynolds-number flows is what the Reynolds number effects are on the mean and statistical turbulence quantities. One of the fundamental tenets of boundary-layer research is the idea that, for a given geometry, any statistical turbulence quantity (mean, rms, Reynolds stress, etc.) measured at different facilities and at different Reynolds numbers will collapse to a single universal profile when nondimensionalized using the proper length and velocity scales. (Different scales are used near the wall and away from it.) This is termed self-similarity or self-preservation and allows convenient extrapolation from the low-Reynolds-number laboratory experiments to the much higher-Reynolds-number situations encountered in typical field applications. The universal log profile

Evaluation of personal aerosol samplers challenged with large particles

The Simplified Test Protocol, developed in our earlier studies for testing personal inhalable aerosol samplers, was evaluated in a specially designed small open-section, close-loop wind tunnel. The sampling efficiencies of three personal inhalable aerosol samplers (IOM, GSP, and Button Aerosol Sampler) were measured with 65 μm particles, using the Simplified Test Protocol at four inlet orientations to the wind ( 0, 90, 180 , and 270°). The results were compared with the data collected from other evaluation approaches. Analysis of variance (ANOVA) has shown that there is no statistically significant difference in the samplers’ performance when they are tested in the small and large wind tunnels following the Simplified Test Protocol and in the large wind tunnel following the conventional approach (samplers on a full-size human manikin). Thus, the Simplified Test Protocol has been shown to be suitable for the performance evaluation of personal inhalable aerosol samplers. The new wind tunnel facility was also found useful for handling very large particles, which is a considerable advantage over traditional wind tunnels. Our new wind tunnel was successfully used to measure the sampling efficiencies of the IOM, GSP, and Button Aerosol Sampler when challenged with particles of up to approximately 250 μm aerodynamic diameter at wind velocities of 50 and 100 cm s −1 . The data show that the sampling efficiency of the IOM sampler depends significantly on the wind velocity and is above 100% for particles of 165 and 241 μm mass median aerodynamic diameter. This dependence is not statistically significant for the GSP and Button Aerosol Sampler, whose sampling efficiencies are similar to each other and do not change with increasing test particle size at the indicated wind velocities. Also, the sampling efficiencies of the GSP and Button Aerosol Sampler closely follow the independent data obtained by using a breathing and rotating manikin at a wind velocity of 100 cm s −1 . The new wind tunnel design is expected to enhance the ability to extend the inhalable convention beyond 100 μm .

A 3-D tolerant wind tunnel for general wind engineering tests

A tolerant wind tunnel for general wind engineering model tests is developed. Results for five different test models representing a building and four different road vehicles are presented and discussed. They show the danger of testing larger models in the traditional solid wall and open jet wind tunnels with a consequence of very large-wall corrections. On the other hand, they indicate clearly the effectiveness of the airfoil-slatted test section over a certain range of open-area ratios (OAR), at which a nearly zero-blockage test environment is obtained. Thus, a concept of model-blockage tolerance range is defined. Tunnel configurations and model sizes are recommended, and suggestions for building model tests in an atmospheric boundary layer flow are given.