Abstract:

ESDU 91028 provides a method based on the Nash and Bradshaw equation extended for the effects of compressibility. To evaluate the equation, both the pressure distribution and the development of the momentum thickness are required. At an early design stage it is unlikely that the boundary layer development will be known, and so the method due to Spence, modified for compressibility, is used to calculate momentum thickness. That ensures compatibility with the derivation of the Nash and Bradshaw equation and provides a method for wholly turbulent boundary layers that is independent of Reynolds number. The Nash and Bradshaw equation has been compared with BVGKE calculations and found to agree within 5 per cent for subcritical flow. Comparisons of using three other boundary layer models in place of the Spence method gave results within 3 per cent of those obtained by the method used here provided boundary layer transition was within 0.1 of chord from the leading-edge and the excrescence was at least 0.1 of chord aft of transition. A Fortran program of the method is provided as ESDUpac A9128, and information on the input and output format is included together with a number of worked example calculations illustrating its use.