Accelerated Convergence to Steady State by Gradual Far-Field Damping

Reflections from artificial boundaries inhibit convergence of transient solutions to their steady limit. Far-field damping operators to suppress such reflections are presented for general first order hyperbolic systems, and particular reference is made to the compressible Euler equations. T h e damping operator has the following properties: (a) No reflections are generated due to the introduction of the clamping terms and (b) Different wave systems may be damped a t different rates. Feature (a) enables the attenuation of waves over relatively short length scales, while feature (b) enables the damping operator t o act selectively on the outgoing waves alone, leaving the incoming waves unharmed. This property is desirable in genuine timedependent problems where consistent information should be allowed t o propagate from the artificial boundaries. Results for compressible Euler flows past aerofoils show the potential of far-field damping in substantially accelerating, particularly in fully subsonic problems.