Interactive planar multi-blade flows with a global angle of attack

Abstract

Planar flow past multiple successive blades and wakes is studied for locally non-symmetric blades aligned with a global angle of attack to the oncoming freestream. The typical blade lies relatively near the centreline of the oncoming wake from the preceding blade but is shifted due to the global attack angle. The central flow structure is of a periodic, pressure interactive boundary-layer over each blade and wake, embedded within a slowly growing Blasius-type flow. This is coupled through the inviscid outer flow via a pressure–displacement relationship. Differing amendments to this structure occur as the global angle of attack is increased in magnitude. The local and global non-symmetries require a leading-edge jump in pressure and velocities in the inner boundary-layer to ensure that the Kutta condition is satisfied at the trailing edge. The flow structure is described for a range of angles of attack, and numerical results are presented for the two cases of most interest where the innermost periodic layer is directly influenced by the global features. Studies are restricted to the condensed limit here. Separation is found to occur and can be caused by both local and global influences.