Simplified Approach to Predicting Rough Surface Transition

Abstract

Turbine vane heat transfer predictions are given for smooth and rough vanes where the experimental data show transition moving forward on the vane as the surface roughness physical height increases. Consistent with smooth vane heat transfer, the transition moves forward for a fixed roughness height as the Reynolds number increases. Comparisons are presented with published experimental data. Some of the data are for a regular roughness geometry with a range of roughness heights, Reynolds numbers, and inlet turbulence intensities. The approach taken in this analysis is to treat the roughness in a statistical sense, consistent with what would be obtained from blades measured after exposure to actual engine environments. An approach is given to determine the equivalent sand grain roughness from the statistics of the regular geometry. This approach is guided by the experimental data. A roughness transition criterion is developed, and comparisons are made with experimental data over the entire range of experimental test conditions. Additional comparisons are made with experimental heat transfer data, where the roughness geometries are both regular and statistical. Using the developed analysis, heat transfer calculations are presented for the second stage vane of a high pressure turbine at hypothetical engine conditions.

Extension of the algebraic transition model for the wall roughness effect

“…It follows for the distribution of the intermittency coefficient that measured transition length is somewhat shorter than the predicted one. According to Boyle and Stripf [2], the correlation for the transition length was not modified for roughness effects. This assumption should be probably revised.…”

“…Provided that the Blasius boundary layer exists in the laminar part of the boundary layer, the non-dimensional equivalent sandgrain roughness can be correlated to the ratio Nevertheless, results of experimental investigation of the transition on a rough flat plate with sand paper carried out by Pinson and Wang [17] and Jonáš et al [18] show that the wall roughness influences the transition onset for values k s + < 5. Therefore, the transition correlation of Boyle and Stripf [2] was modified to the form…”

“…The contribution deals with a short review of existing correlations for the transition onset including a modified criterion of Boyle and Stripf [2] and with its testing by means of selected test cases -incompressible flat plate flow and compressible flows through a linear turbine blade cascade.…”

Modification of the Algebraic Transition Model for Wall Roughness Effect Including a Rough Strip

“…Several correlations were proposed based on these experiments where wall roughness was modelled by regularly distributed truncated cones with various distances (see e.g. Boyle and Stripf [6] and Langtry and Menter [7]). The correlation of Boyle and Stripf [6] was modified for low values of roughness height by Straka and Příhoda [8].…”

“…Boyle and Stripf [6] and Langtry and Menter [7]). The correlation of Boyle and Stripf [6] was modified for low values of roughness height by Straka and Příhoda [8]. All current relations were proposed for the various types of distributed wall roughness covering the whole surface.…”