Turbulent boundary layers with foreign gas transpiration

Blowing through the wall is one of the most efficient methods to influence the characteristics of a turbulent boundary layer such as heat transfer, sk in friction, boundary-layer profiles, and flow separation. The most importa nt technical application is to cool a permeable wall with a coolant mass fl ow through the wall, known as transpiration cooling. Designing transpiratio n-cooled devices requires the knowledge of empirical correlations for the c alculation of skin friction and heat transfer in the case of blowing. The r esults of velocity and temperature boundary-layer profile measurements made at the Dresden University of Technology were used to characterize the infl uence of foreign gas transpiration on skin friction and heat transfer. Simp le empirical correlations describing skin friction and heat transfer reduct ion as functions of the blowing ratio and especially the blowing pas proper ties were found. Further investigations deal with flow separation due to bl owing, and a universal critical blowing parameter is defined. The empirical correlations have also been verified by means of a numerical calculating p rocedure. Measurements made at the German Aerospace Center in Lampoldshause n using an H-2/O-2 combustion chamber delivered experimental heat transfer results in the case of hot gas parameters according to practical applicatio ns.