An experimental study was made of the effect of a favorable pressure gradient on the Reynolds analogy factor, K = 2St/C sub f, for a natural two-dimensional supersonic turbulent boundary layer in air. Integrated values of the skin friction coefficient and Stanton number were determined from experimental data. The results show that Colburn's value of K = Pr to the - 2/3 power, which was found empirically from zero pressure gradient data, is satisfactory for relating skin friction and heat transfer for the magnitudes of pressure gradients investigated. (Author).

Experimental investigation in turbulent boundary layer flows represents one of the canonical geometries of wall bounded shear flows. Utmost relevance of such experiments, however, is applied in the engineering applications in aerospace and marine industries. In particular, continuous effort is being imparted to explore the underlying physics of the flow in order to develop models for numerical tools and to achieve flow control. Flow control experiments have been widely investigated since 1930’s. Several flow control technique has been explored and have shown potential benefit. But the choice of control technique depends largely on the boundary condition and the type of application. Hence, friction drag of subsonic transport aircraft is intended to be reduced within the scope of this Ph. D. topic. Therefore, application of active control method such as microblowing effect in the incompressible, zero pressure gradient turbulent boundary layer was investigated. A series of experiments have been performed in two different wind tunnel facilities. Wind tunnel from Department of Aerodynamics and Fluid Mechanics (LAS) was used for the measurements for moderate Reynolds number range in co-operation with the wind tunnel from Laboratoire de M´ecanique de Feiret Lille for large Reynolds number range. Measurements are conducted with the help of state-of-the-art techniques such as Laser Doppler Anemometry, Particle Image Velocimetry and electronic pressure sensors.

This study examined the effect of mild pressure gradients on the mean and turbulent flow of high-speed boundary layers. Three Mach numbers (1.7, 3.0 and 5.0) were investigated. Three pressure gradients were examined; a zero pressure gradient (ZPG), a favorable pressure gradient (FPG), and a combined pressure gradient (CPG). The CPG consisted of an adverse pressure gradient followed by a favorable pressure gradient. Conventional pressure probes, hot- wire and particle image velocimetry (PIV) were used to examine the flow. Measurement included mean velocity, velocity turbulence intensity, mass flux turbulence intensity and energy spectra. Instantaneous (10 nsec) Mie scattering flow visualizations were acquired. Qualitatively, the flow visualizations indicated that the turbulent flow structures were strongly affected by the pressure gradients. For the Mach 2,8 case, the PIV contours and the hot-wire profiles both indicated that the boundary layer thickness increased by 40% and decreased by 100% relative to the ZPG for the favorable and adverse pressure gradients, respectively. Further, the PIV and hot-wire data indicated that the axial turbulence intensity levels increased by 22% for the CPG and decreased by 25% for the FPG. The energy spectra data indicated that once a pressure gradient was applied (favorable or adverse) the low frequency energy increased followed by a rapid decay. Lastly, it was found that nominally 20 to 30 PIV images were sufficient for mean flow boundary layer velocities, but 93 images (the maximum recorded in this study) were insufficient to adequately resolve Reynolds shear stresses.