Chapter 11 - Further development and applications of vortex cloud modelling to lifting bodies and cascades

Summary

Introduction

A basic outline of full vortex cloud modelling was presented in Chapter 10 but with limited application primarily to bluff body flows for which separation occurs spontaneously and dramatically at reasonably cetain separation points, resulting normally in the development of a broad periodic wake. The main aim of this chapter is to apply the full vortex cloud method to lifting bodies such as aerofoils and cascades for which the aerodynamic aim usually is to avoid flow separations, maintaining low losses. Full vortex cloud modelling represents an attempt to solve the Navier– Stokes equations including both the surface boundary layer near field and the vortex wake far field flows. Boundary layer separations are then self-determining. In practice however, as discussed by Porthouse & Lewis (1981), Spalart & Leonard (1981) and Lewis (1986) vortex cloud modelling in its present state of development seems unable quite to cope with the general problem of boundary layer stability and various techniques are proposed by these authors to avert premature stall as often experienced during vortex cloud analysis of aerofoils or cascades. These problems will be considered in Sections 11.2–11.4. Extension of vortex cloud modelling to cascades will be given in Section 11.5 and studies of acoustic excitation due to wake vortex streets from bluff bodies in ducts are briefly discussed in Section 11.6.