Transition Studies and Skin Friction Measurements on an Insulated Flat Plate at a Hypersonic Mach Number

Citation

Korkegi, Robert Hani (1954) Transition Studies and Skin Friction Measurements on an Insulated Flat Plate at a Hypersonic Mach Number. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/X3B9-VW73. https://resolver.caltech.edu/CaltechETD:etd-01072004-114554

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. An investigation of transition and skin friction on an insulated flat plate, 5 x 26 inches, was made in the GALCIT 5 x 5 inch Hypersonic Wind Tunnel, Leg No. 1, at a nominal Mach number of 5.8. The phosphorescent lacquer technique was used for transition detection and was found to be in good agreement with total-head rake measurements along the plate surface and pitot boundary layer surveys. It was found that the boundary layer was laminar at Reynolds numbers of at least 5 x 10[superscript 6]. It was also observed that transverse contamination due to the turbulent boundary layer on the tunnel sidewall originated far downstream of the flat plate leading edge at Reynolds numbers of 1.5 to 2 x 10[superscript 6], and spread at a uniform angle of 5 1/2[degrees] compared with 9 1/2[degrees] in low speed flow. The effect of two-dimensional and local disturbances was investigated. The technique of air injection into the boundary layer as a means of stimulating transition was extensively used. It was observed that, although the onset of transition occurred at Reynolds numbers down to 10[superscript 6], a fully developed turbulent boundary layer was not obtained at Reynolds numbers much below 2 x 10[superscript 6] regardless of the amount of air injected. A qualitative discussion of these results is given with emphasis on the possibility of a greater stability of the laminar boundary layer in hypersonic flow than at lower speeds. Direct skin friction measurements were made by means of the floating element technique incorporating a null system using chain loading, over a range of Reynolds numbers (based on distance from leading edge) from 10[superscript 6] to 4 x 10[superscript 6]. Without artificial tripping, the boundary layer was verified as being laminar over the complete range. With air injection, turbulent shear was obtained only for Reynolds numbers greater than 2 x 10[superscript 6] , this value being in good agreement with earlier results of this investigation. The turbulent skin friction coefficient was found to be approximately 0.40 of that for incompressible flow for a constant value of R[subscript theta], and 0.46 for an effective Reynolds number between 5 and 6 x 10[superscript 6].

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