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A Review of Roughness-Induced Nosetip Transition

1983; American Institute of Aeronautics and Astronautics; Volume: 21; Issue: 1 Linguagem: Inglês

10.2514/3.60102

1533-385X

R. G. Batt, Hartmut H. Legner,

Gas Dynamics and Kinetic Theory

HE re-entry physics community has for many years recognized the crucial role that nosetip transition plays in re-entry vehicle performance. The onset and progression of the transition front are governed by complex fluid mechanical processes that depend critically on surface roughness, wall temperature, nose-tip geometry, angle of attack, and freestream conditions. The flight analyst must make preflight predktioil~ and postflight data comparisons incorporating a suitable transition model in shape-change code computations. Such calculations of vehicle drag and surface recession contours are sensitive to both the transition correlation and the surface roughness. This sensitivity of nosetip shape change is dramatic, as witnessed by calculated that show that moderate changes in either the surface roughness height (keeping the correlation fixed) or the transition correlation slcne (keeping the roughness fixed) lead to markedly different transition-onset altitudes and nosetip shapes. These vehicle shape-change effects, which are in direct response to the transition process, are further compounded by the inherent stochastic behavior of boundary-layer transition and the .random nature of nosetip-surface roughness. Resulting transition front asymmetries can promote asymmetric nosetip shapes that cause substantial vehicle trim dispersions. The importance of the two key aspects of nose:ip transition, i.e., the transition correlation model and the roughness character, has, of course, been pointed out by previous investigators. Although individual experiments or analyses have been self-contained and have adequately described most of the observed behavior, there still exists in the literature a lack of consistency among the various studies with regard to 1) roughness height definition, 2) transition point identification, and 3) validity and/or interpretation of specific experimental transition data. These deficiencies have limited the extent to which previo:~~ studies can be applied and have provided the primary motivation for the present investigation. The current paper, which essentially summarizes results obtained from the detailed study rer~orted in Ref. 2, reviews previous research on nosetip transition, re-examines surface roughness characterization, and describes a nosetip correlation model bascd in part on thc critical Reynolds number approach as well as on a re.cvaluation of experimental data. In the sections that follow, the emphasis will be upon the consistent evaluation and detailed review of the ground-test data on nosetip transition. A common roughness height definition is developed and subsequently used to reanalyze the data base for wind tunnel, ballistic range, and free-flight experiments.