ABSTRACT: Transonic wind tunnels (TWT) are sophisticated tools for the investigations of flows with Mach numbers of order one. The most characteristic feature of a facility such as this is, for sure, the openings in the walls of the test section. The openings in the walls permit the proper relief effect, and this, on the other hand, makes possible the experimentation at the transonic range. The results to be presented in this paper correspond to an analysis of the flow in the test section of a TWT containing a NACA 0012 airfoil. Both numerical and experimental investigations were conducted. For the numerical investigation, a three-dimensional, finite-difference code, based on the diagonal algorithm, was employed, whereas for the experimentation, the classical static-pressure taps as well as the pressure sensitive paint (PSP) techniques were used. The classical static-pressure tap method is indicated as PSI technique. The pressure distributions were investigated for Mach numbers in the range of 0.6 - 0.8 and angles of attack from 0º up to 8º. The relief effect due to the slots, which provides for avoiding choking effects, is clearly demonstrated when one compares the flow along both solid and perforated walls. In the first part of this research report, the main focus will be on the numerical results. Notwithstanding this, and for comparison purposes, some experimental results will be called upon here, together with some literature data.

ABSTRACT: This research project focuses upon the wake behind a two-dimensional blunt-trailing-edged body. Data are obtained numerically by means of a Direct Numerical Simulation code. The body has an elliptical nose followed by a straight section that ends in a blunt base. The present paper is dedicated to the analysis of the onset of the shedding process. The effort is certainly worthwhile, because, in contrast to the case of the circular cylinder, the boundary layers's separation points are defined and fixed. This allows a better assessment of the vital influence of the boundary layers upon the wake, in a controlled way. This is not the case for the circular cylinder, because, in this instance, the separation points oscillate in relation to a mean position. In the present analysis, the relationship between the onset of shedding Reynolds number, RehK , and the aspect ratio, AR, is obtained. To this end, a wide range of aspect ratios, between 3 and 25, was investigated. The result represented by this relationship is a novelty in the literature. Values of RehK are strongly influenced by the aspect ratio for the case of the short cylinders - for which AR is low. After AR about 9, the curve flattens and the influence of the aspect ratio upon the shedding Reynolds number is very mild. Besides, the paper discusses another very important aspect; the overall stability of the pre-shedding laminar bubble at the base of the body. It is important to stress that the latter study relies on the fact that the boundary layers separation points are fixed.

This work describes a lumped parameter mathematical model for the prediction of transients in an aerodynamic circuit of a transonic wind tunnel. Control actions to properly handle those perturbations are also assessed. The tunnel circuit technology is up to date and incorporates a novel feature: high-enthalpy air injection to extend the tunnel’s Reynolds number capability. The model solves the equations of continuity, energy and momentum and defines density, internal energy and mass flow as the basic parameters in the aerodynamic study as well as Mach number, stagnation pressure and stagnation temperature, all referred to test section conditions, as the main control variables. The tunnel circuit response to control actions and the stability of the flow are numerically investigated. Initially, for validation purposes, the code was applied to the AWT ("Altitude Wind Tunnel" of NASA-Lewis). In the sequel, the Brazilian transonic wind tunnel was investigated, with all the main control systems modeled, including injection.