Search

Infrared-image technique has been prevailingly applied to diagnose laminar-turbulent transition in compressible boundary layers. The purpose of the present paper is to establish this technique for low subsonic flow. To produce measurable temperate difference between laminar and turbulent states above ambient temperature, the model was pre-heated by a hair-drier prior to each measurements. Infrared image captured in two-dimensional boundary layer was quantitatively reduced to evaluate transition location. It was found that reduced results are in good agreement with those by means of conventional methods such as hot-wire anemometer and Preston tube., 資料番号: AA0032827015, レポート番号: NAL SP-54

境界層安定性について超音速風洞試験および数値解析を行った。風洞試験は後退翼モデルについて行った。境界層遷移位置をいくつかの迎え角で観測し、境界層吸気による層流域の拡大も観測した。その結果は超音速層流制御の妥当性を示した。線形安定性理論にもとづいて、境界層安定解析コードを開発し、その妥当性を2次元の境界層について確認した。風洞試験結果のひとつを解析し、擾乱の特性を明らかにした。, Supersonic wind tunnel tests and numerical analyses were carried out on the boundary layer stability. Wind tunnel tests were performed on a swept wing model. Boundary layer transition locations were detected at various angles of attack and extensions of laminar flow regions by boundary layer suction were also observed. Consequently, the validity of supersonic laminar flow control was suggested. And a boundary layer stability analyses code was developed, based on the linear stability theory, and its validity was confirmed for two dimensional boundary layers. Then one of the wind tunnel test cases was analyzed, and characteristics of disturbances were clarified., 資料番号: AA0000440006, レポート番号: NAL SP-31

A numerical method for computing unsteady two-dimensional boundary layers in incompressible laminar and turbulent flows is described and applied to a single airfoil changing its incidence angle in time. The solution procedure adopts a first order panel method with a simple wake model to solve for the inviscid part of the flow, and an implicit finite difference method for the viscous part of the flow. Both procedures integrate in time in a step-by-step fashion, in the course of which each step involves the solution of the elliptic Laplace equation and the solution of the parabolic boundary layer equations. The Reynolds shear stress term of the boundary layer equations is modeled by an algebraic eddy viscosity closure. The location of transition is predicted by an empirical data correlation originating from Michel. Since transition and turbulence modeling are key factors in the prediction of viscous flows, their accuracy will be of dominant influence to the overall results. NASA ORDER C-80017-F; RTOP 582-01-11 Approved for public release; distribution is unlimited.

Measurements of spatiotemporal correlations of fluctuations of temperature at three points are carried out to determine the structure on a large scale of the internal zone of a boundary layer which on the average is two-dimensional. It is shown that perturbations of air exist, conservative along the mean and three-dimensional motion, the lateral coherence of which is less than the thickness of the boundary layer. The comparative study of double and triple correlations shows the existence of two statistically dominant principal modes: one corresponds to perturbations coming from near regions of the wall, the other from near regions of the external flow.