Computational Modelling of Transonic Circulation Control

Abstract

This Ph.D. thesis focusses upon computational fluid dynamics simulations of circulation control in transonic freestream speeds for applications to unmanned combat air vehicles. The work addresses Coanda shape designs and their effectiveness for transonic circulation control using supersonic jets, with comparisons against traditional control surfaces. Previous works have thus far only investigated transonic circulation control on elliptical sectioned wings with unrepresentatively thick trailing edges and improvements in performance made by considering elliptical Coanda devices or increasing radii of curvature. In this work, a supercritical aerofoil was first modified to accommodate a small Coanda surface with minimal effects on the base drag and a comparison made between the performance of using several Coanda designs and a hinged control surface. The use of a step was demonstrated to make a circulation control device with a simple converging nozzle as effective as ailerons and flaps up to moderate deflection angles and that the limitations are due to breakdowns in the mean flow in a similar fashion to traditional devices. In addition an optimisation study was performed using modern numerical methods on the contouring of the Coanda surface, which identified a shape that performed well for both transonic and subsonic freestream conditions. Circulation control was then applied to a three-dimensional unmanned combat air vehicle planform and assessed at transonic conditions for use in roll, pitch and yaw control. From the range of conditions investigated the findings suggest that, for a three-dimensional representative geometry, circulation control can match the performance of conventional controls for roll and pitch. The results also suggest that for benign transonic conditions, circulation control can also provide control similar effectiveness to split flaps for yaw control. The findings open up insights into transonic circulation control and hopefully will promote further research in both academia and industry, where a lack of CFD validation quality experimental data for a transonic test case with supersonic blowing prohibits the technology from advancing.