ABSOLUTE AND CONVECTIVE STABILITY ANALYSE S OF VELOCITY PROFILES OF AMOTOR-VEHICLE USING AN ORR-SOMERFELD ANALYTIC APPROACH

The experimentally measured, time averaged velocity profiles in the tu rbulent wake behind a motor vehicle are studied on absolute and convec tive instability using an analytic Orr-Sommerfeld approach. An absolut ely unstable domain coinciding approximately with the domain of the qu asistationary reverse flow in the wake was identified. This allows us to suggest that wake control, e.g. by means of a base bleed, for the p urpose of reduction of the resistance is possible. This suggestion is confirmed by a first principle experiment.