University College London
London, United Kingdom
Initial-value problems are to be discussed for planar inviscid disturbances in streamlined near-wakes. This is mostly for those areas of near-wake flow where the basic motion comprises nearly uniform shear with or without normal influx into the accompanying viscous interfacial layer, although agreement is found with linear properties for full velocity profiles of double-Blasius, double-Jobe-Burggraf, Hakkinen-Rott and Goldstein form. With nonlinear disturbances, general non-wave initial conditions lead to a new integro-partial-differential amplitude equation which is studied analytically and numerically. The solutions show decay, finite-time blowup or nonlinear up-stream-travelling disturbances. Absolute and upstream- or downstream-convective instability is encountered; in generic cases nonlinearity can be shown analytically to provoke upstream convection. Comparison will be made with three-dimensional behaviour in the linear case and with a direct simulation in the nonlinear regime.