An investigation of vorticity amplification in stagnation flow

Abstract

Recently a theory which could explain satisfactorily the strong sensitivity of stagnation-point heat transfer and skin friction on cylinders in cross flow to relatively small turbulent fluctuations in the free-stream was put forth by Sutera et al. [11. This mathematical model proposed that vorticity amplification due to stretching of vortex filaments in the strongly diverging flow near the stagnation point is the underlying mechanism. The basic physical ideas and mathematical formulations relating to vorticity amplification by stretching and the resulting effects on flow, heat transfer and skin friction at a two-dimensional stagnation point were set forth in Reference 1 and in a subsequent paper by Sutera E2]. This theory was later extended to the outer flow field, i.e., outside and far from the boundary layer, by Sadeh et al. I31. Thus, a detailed review of the vorticity-amplification theory need not be repeated here. The primary purpose of the present investigation was the experimental verification of the vorticity-amplification theory presented in References 1, 2 and 3. The experimental work was designed mainly to obtain quantitative evidence of vorticity amplification by stretching and its effects on the average boundary-layer profile. A search for the prezlicted vortex structure near the wall was also carried out.