Threshold Amplitudes for Transition in Channel Flows

The threshold amplitude for subcritical transition in Poiseuille and Couette ows is investigated. For Poiseuille ow we present examples where the threshold scales like R ?7=4 for 1500 R 5000, where R is the Reynolds number. For Couette ow we present an example where the threshold scales like R ?5=4 for 500 R 2000.