Throat Heating Effect on Critical Roughness and Nozzle Wall Boundary-Layer Stability

The effect of wall heating in the throat region on the flow quality in a Mach 3.5 and a Mach 2.4 axisymmetric nozzle is investigated. Because of the boundary-layer thickening effect, the critical roughness height to trigger laminar-turbulent transition is larger in the heated cases. Therefore, for a...

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Bibliographic Details
Published in:AIAA journal 2003-04, Vol.41 (4), p.612-622
Main Authors: Lin, R.-S, Iyer, V, Malik, M. R
Format: Article
Language:English
Subjects:
Exact sciences and technology
Flows in ducts, channels, nozzles, and conduits
Fluid dynamics
Fundamental areas of phenomenology (including applications)
Heating
Nozzles
Physics
Surface roughness
Systems stability
Turbulence control
Turbulent flows, convection, and heat transfer
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Summary:The effect of wall heating in the throat region on the flow quality in a Mach 3.5 and a Mach 2.4 axisymmetric nozzle is investigated. Because of the boundary-layer thickening effect, the critical roughness height to trigger laminar-turbulent transition is larger in the heated cases. Therefore, for a given surface finish, the adverse effect of roughness on transition can be minimized by sufficient wall heating. However, the combined effect of heating and pressure gradients is to introduce an overshoot in the streamwise velocity profile, as earlier predicted by Cohen and Reshotko. Associated with this overshoot is a new generalized inflection point near the edge of the boundary layer, and, as a consequence, the nozzle wall boundary layer supports high-frequency two-dimensional inviscid disturbances. N-factor results indicate that, with excessive throat heating, these disturbances could cause premature transition downstream of the throat and, hence, jeopardize the quiet performance. Therefore, favorable (on critical roughness height) and adverse (on boundary-layer instability) effects of heating have to be carefully evaluated. Mean flows are computed by using both a boundary-layer code and a Navier-Stokes solver, the critical roughness heights are calculated based on an empirical formula, and the destabilizing effect of heating is evaluated by using compressible linear stability theory. The critical roughness heights are established for the two nozzles for given heating strips. [PUBLICATION ABSTRACT]
ISSN:0001-1452
1533-385X
DOI:10.2514/2.2015