MEASURING INSTANTANEOUS FLUID DYNAMIC FORCES ON BODIES, USING ONLY VELOCITY-FIELDS AND THEIR DERIVATIVES

We present an exact expression for the evaluation of instantaneous for ces on a body in an incompressible cross-flow which only requires the knowledge of the velocity and vorticity field in a finite and arbitrar ily chosen region enclosing the body. This expression is particularly useful for experimental techniques like Digital Particle Image Velocim etry (DPIV) which provide instantaneous, 2-D velocity and vorticity fi elds but not pressure fields. The present formula is tested on a numer ical flow simulation using a high-resolution vortex method and experim entally with DPIV on a circular cylinder flow. (C) 1997 Academic Press Limited.