Flow past a thin wedge in a wind tunnel with partially perforated walls at high subsonic velocities

The problem of flow past a thin two-dimensional wedge at high subsonic velocity in a wind tunnel with partially perforated walls is considered for low suction flow rates. The solution of this model problem may be used in determining the optimal parameters of the suction system for which the aerodynamic characteristics in the tunnel are closest to those in an unbounded stream.In conclusion the author wishes to thank E. M. Kalinin for suggesting the study of this problem.     

Flow blockage in model testing in the perforated working section of a wind tunnel as M∞→1

The third flow blockage regime associated with the finite length of the perforated tunnel walls is investigated. In the case of infinitely long permeable boundaries blockage is impossible, since all the air displaced by the body can flow out through the walls even when their permeability is very low. If, however, the length of the permeable boundary is finite, blockage is in principle possible, given a low degree of permeability.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 151–157, May–June, 1991.The authors are grateful to Yu. B. Lifshits for useful comments.     

Progress in wind tunnel experimental techniques for wind turbine

Based on the unsteady aerodynamics experiment (UAE) phase VI and the model experiment in controlled conditions (MEXICO) projects and the related research carried out in China Aerodynamic Research and Development Center (CARDC), the recent progress in the wind tunnel experimental techniques for the wind turbine is summarized. Measurement techniques commonly used for different types of wind tunnel experiments for wind turbine are reviewed. Important research achievements are discussed, such as the wind tunnel disturbance, the equivalence of the airfoil inflow condition, the three-dimensional (3D) effect, the dynamic inflow influence, the flow field structure, and the vortex induction. The corresponding research at CARDC and some ideas on the large wind turbine are also introduced.     

Experimental investigation of a hybrid wind tunnel model

New developments in power electronics (such as the linear motor) may be of great advantage for future economic aerodynamic testing. After a comprehensive review of economical aspects of present wind tunnel technologies, the experimental verification of the hybrid wind tunnel concept will be presented. A scale law is derived to extrapolate the experimental results of the model-HWT to a facility size for simulating full scale Re-numbers. Finally, methods will be discussed by which the flow constancy during the running time may be improved.List of symbols A area - a velocity of sound - d diameter - i influence region - l length - Ma Mach number - m facility mass - n exponent in power law of boundary layer profile u/u ₂ = (y/)^1/n - P power - p pressure - q kinetic pressure (=(/2)u ²) - Re Reynolds number - r radius - t time - u, w velocity - V volume - x, y coordinates - boundary layer thickness - ^* boundary layer displacement thickness - velocity deficit at boundary layer edge (usually defined as = 0.01) - windtunnel efficiency factor - efficiency - ratio of specific heats - test facility mass ratio - kinematic viscosity - normalized coordinate - mass density - stress - ( )_1,2,3 flow region (Fig. 1) presuffix 0 signifies - ( )_2,2,2 flow state (Figs. 7; 11) stagnation condition - ( ) test section values - ( ) _c cryo-windtunnel - ( ) _d diffusor - ( ) _D model drag - ( ) _el electric - ( ) _ew1 head of expansion wave - ( ) _ew2 tail of expansion wave - ( ) _f fan - ( ) _fs fan shaft - ( ) _mt model tunnel - ( ) _N normal temperature windtunnel - ( ) _or original tunnel - ( ) _r,l right, leftrunning waves - ( ) _rp wind tunnel return pipe - ( ) _s suction tube - ( ) _sl test sled - ( ) _sw shock wave - ~ relative system - - values normalized with a ₁ or p ₁ - ETW European Transonic Windtunnel (early, noncryogenic concepts. A = 21 m₂) - HWT Hybrid-Wind-Tunnel - LIM Linear Induction Motor - LN₂ Liquid Nitrogen - LT Ludwieg-tube     

Excitation of velocity fluctuations and noise in a wind tunnel

The aim of this paper is to develop a theory, consistent with the observations, of the nature and location of the structures that determine self-excitation and the emission of the narrow-band components of the noise generated by the open working section of wind tunnels. At the same time, the theory is applied by using it as a basis for constructive solutions.Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.4, pp. 165–173, July–August, 1992.     

Theoretical and experimental investigations of wall adaptation control in wind tunnel and hybrid wind tunnel testing

The hybrid wind tunnel principle is an economical alternative to classical wind tunnels. Wall adaptation tests are reported which are performed in a small scale arrangement duplicating original kinematic relations. A new method for controlling the quality of wall adaptation is presented which is based on the pressure distribution at the rigid wall. This procedure may also be applied for wall adaptation in conventional wind tunnel technique.The experimental investigations reported here have been carried out by the following students in the course of undergraduate work: Ch. Bauer, C. Schultes, Th. Reimer and U. Walter. I am very grateful for their great care accomplished contributions.     

Thermally stratifying a wind tunnel for buoyancy influenced flows

A novel method of heating wind tunnel flows to strong thermal stratifications is described. Variable electric heating is employed to create user-selectable temperature profiles in steady, uniform mean flow. Linear temperature gradients of up to 200 °C/m (Väisälä frequencies of 2.5 rad s^-1) can be sustained. The performance of the facility is discussed in the context of continuously-stratified grid-generated turbulence, although it is useful for a broader set of applications. The flow field is found to be free of deleterious natural convection and internal wave effects. The departure from homogeneity of grid-generated, stratified turbulence in the facility is roughly ±10% away from the wall influenced regions.     

Evaluation of a new wind tunnel with expanding corners

A new low-speed, closed-circuit, closed-test-section wind tunnel, called BLT, has been designed and built at KTH. The turbulence intensity in the test section is <0.04%, the total pressure variation is <±0.1% and the temperature variation is <±0.07°C over the cross-sectional area. The concept of expanding corners with an expansion ratio of 1.32 first investigated by Lindgren et al. in 1998, has been implemented successfully with a two-dimensional total pressure loss coefficient of 0.047 at a chord Reynolds number of 200,000. It is comparable to or even better than the values found in most wind tunnels using nonexpanding corners. The findings in this study prove the usefulness of expanding corners to achieve a compact wind tunnel circuit design without compromising the flow quality.     

Gas dynamics of a low-pressure chamber in a high-enthalpy short-duration wind tunnel

Gas dynamics of a low-pressure chamber in a double-chamber hotshot wind tunnel is considered. The time needed to fill the second chamber is in good agreement with the value obtained by examining the quasi-steady process of emptying and filling of the high-pressure and low-pressure chambers. The transitional process is strongly affected by wave processes in the channel between the chambers. By changing the place of the throttling grid in this channel, one can change the time of filling of the second chamber (decrease it severalfold). The examined schemes of air input into the second chamber ensure its complete deceleration. The Mach number at the exit of the second chamber (in the wind-tunnel nozzle throat) is almost constant over the cross section and close to unity.Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 1, pp. 29–43, January–February, 2005.     

One-dimensional transonic gas flow in a wind tunnel with perforated walls

Near-sonic inviscid gas flow in the working section of a wind tunnel with perforated walls is investigated in the context of the one-dimensional theory with Darcy's boundary condition.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 143–148, November–December, 1988.     

Methods for investigating supersonic ground effect in a blowdown wind tunnel

Two methods to experimentally investigate supersonic ground effect problems in a wind tunnel have been examined to determine their relative effectiveness compared to a more realistic, but physically unfeasible, representation of the ground effect by means of a moving ground. Experimental data were compared with the results of numerical simulations. The latter, once validated against pressure data from the wind tunnel, confirmed that generally a symmetry technique is more suitable than an elevated ground approach.     

CFD wind tunnel test: Field velocity patterns of wind on a building with a refuge floor

This paper reports a CFD wind tunnel study of wind patterns on a square-plan building with a refuge floor at its mid-height level. In this study, a technique of using calibrated power law equations of velocity and turbulent intensity applied as the boundary conditions in CFD wind tunnel test is being evaluated by the physical wind tunnel data obtained by the Principal Author with wind blowing perpendicularly on the building without a refuge floor. From the evaluated results, an optimised domain of flow required to produce qualitative agreement between the wind tunnel data and simulated results is proposed in this paper. Simulated results with the evaluated technique are validated by the wind tunnel data obtained by the Principal Author. The results contribute to an understanding of the fundamental behaviour of wind flow in a refuge floor when wind is blowing perpendicularly on the building. Moreover, the results reveal that the designed natural ventilation of a refuge floor may not perform desirably when the wind speed on the level is low. Under this situation, the refuge floor may become unsafe if smoke was dispersed in the leeward side of the building at a level immediately below the refuge floor.