Design of turbine cascades with transitional profile boundary layers

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Alarcon, Gabriel
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Mechanical Engineering
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A computer based "direct" design system for two-dimensional turbine airfoils in cascade is developed involving a sequence of calculations in which the airfoil profile is arbitrarily designed from velocity diagram requirements, followed by an inviscid blade-to-blade flow calculation of the velocity distribtuion and the exit gas angle. A transitional boundary layer analysis is then carried out followed by a wake mixing analysis to calculate profile losses and the viscous exit gas angle. The profile design can be rapidly iterated on through adjustment of a number of geometry parameters and the flow analysis repeated until a design is found yielding the lowest profile losses;The inviscid calculation is performed in two steps. A global streamline curvature calculation is first carried out followed by a magnified reanalysis around the leading edge. Wilkinson's streamline curvature method is used employing an improved continuity calculation based on a bracketing technique along with a more accurate differentiation method for curvature calculations. The reanalysis uses finite area technique and a body fitted mesh to reanalyze the flow around the leading edge from the data provided by the global analysis;The boundary layer analysis is performed by using the dissipation-integral method of Walz. The method has been extensively modified in the present application to include improved auxiliary relations in the turbulent calculation, wall curvature effects, free stream turbulence intensity effects on the development of the turbulent boundary layer, natural transition models, separation bubble model, turbulent separation model, and wake mixing calculation;The inviscid-viscous calculation method developed yields results for total pressure loss and exit gas angle which agree well with experimental cascade data.

Tue Jan 01 00:00:00 UTC 1980