Freestream

About: Freestream is a research topic. Over the lifetime, 3428 publications have been published within this topic receiving 56147 citations.

On liquid droplet combustion at high pressures.

Abstract: 2 to 5. It is found that in the upstream there is a wake or heat transfer along the x axis and this wake is larger for higher freestream temperature. On the x axis in the upstream the temperature has a significant change in a short distance near the leading edge and becomes essentially uniform beyond the station x/L = —1.9 (not shown). In the y direction the radiation has a large effect on the temperature field in the range 0 < y/L < 0.2. All of these temperature variations are larger in the case of higher freestream temperatures. In the downstream the temperature variation in the vicinity of the plate should be determined from the boundary-layer equations. Here we show the only results for the optically thick case. For the optically thin case the procedure is quite the same. For gases of finite optical depth the energy equation is a nonlinear integro-differential equation of high complexity; this method may still be applicable but needs extensive computing time.

Experimental study of transonic buffet phenomenon on a 3D swept wing

Abstract: The objective of this paper is to analyze the 3D buffet phenomenon which appears on a swept wing at a high Mach number and/or high angle of attack. This aerodynamic instability induces strong wall pressure fluctuations and as such limits aircraft envelope. Consequently, it is interesting to understand this phenomenon in order to not only improve aircraft performance but also to provide more flexibility during the design phase. Results from two wind tunnel tests on a 3D half wing-body configuration are presented for several freestream Mach numbers (0.78–0.86) and Reynolds numbers (2.83 × 106–8.49 × 106, based on the aerodynamic mean chord). The buffet phenomenon is characterized using steady and unsteady wall pressure measurements. By opposition to the 2D buffet which exhibits rather a well marked peak in the pressure spectra, the 3D buffet is characterized by a broadband bump at a much higher Strouhal number (between 4 and 7 times higher). It is also observed that two different instabilities coexist on th...

Studies on laminar boundary-layer receptivity to freestream turbulence near a leading edge

Abstract: An experimental study of the generation of Tollmien-Schlichting waves and wave packets in a flat-plate boundary-layer by weak freestream turbulence has been conducted with the intent of clarifying receptivity mechanisms. Emphasis was placed upon the properties of such waves at stations as far forward as the minimum critical Reynolds number. It was found that alteration of the flow about the leading edge, due either to an asymmetry associated with lift, or due to a change of the fineness ratio of the leading edge, altered the T-S wave amplitude at early stations. The subsequent growth of the waves proceeded faster than expected according to certain stability theory results. Speculation regarding receptivity mechanisms is made.

Characteristics of the compressible shear layer over a cavity

Abstract: The compressible shear layer over a 3:1 rectangular cavity was investigated using schlieren photography and planer laser imaging at freestream Mach numbers of 1.8, 2.1, 2.8, and 3.5. The purpose of this investigation was to study the characteristics of the shear layer structures and their convective velocity over this Mach number range. Schlieren images show leading- and trailing-edge shock waves, as well as shock waves emanating from the shear layer, which became less prevalent as the Mach number increased. Streamwise planar laser sheet lighting images indicate the existence of organized roller-type structures at the lower Mach numbers studied (M =2.1 and 2.8). These structures became less coherent as the Mach number was increased, although the cavity appears to cause the large-scale structures to persist at higher levels of compressibility than found in planar free shear layers. Plan view images indicate that the two dimensionality of the large-scale structures decreased with increasing Mach number. Autocorrelations performed on single-pulse images show that the structure size decreased 63% when the freestream Mach number was increased from 1.8 to 3.5. By double pulsing the laser at delays of 15, 20, and 25 πs, the evolution of the large-scale structures were investigated and quantie ed. The correlations were found to decrease by 23% for the same nondimensional time when increasing the Mach number from 2.1 to 3.5. From the shift of the peak correlation, the convective velocity was calculated for each case and found to vary laterally across the shear layer. At a lateral location most representative of the large-scale structures in the shear layer, the variation in convective velocity with Mach number was best represented by 0.57 times the freestream velocity.

An Experimental Investigation of Turbulent Slot Injection at Mach 6

Abstract: The use of film cooling for protecting a surface exposed to high temperature air at hypersonic speeds is investigated experimentally. The tests were conducted in a Mach 6 contoured axisymmetric nozzle with a streamlined centerbody. The Reynolds number in the test section was in the range of 1-3.6 X 10 6/in.; and a wall to freestream temperature ratio of 0.635. Heat-transfer distributions downstream of the slot were obtained for various mass flow rates and the effect of injection on the velocity, temperature and Mach number profiles was studied. Correlations for the cooling lengths with the blowing rate parameters X = pjUj/peUe for the various coolants-—air, helium, hydrogen, and argon were obtained. Correlations for the heattransfer rates in the form (1 — q/go.») an