A NEW DEVICE TO MEASURE THE LIFT FORCE ON A PARTICLE IN THE VISCOUS SUBLAYER

The entrainment or resuspension of particles in air or water is a very common phenomenon. It is determined by the fluctuating lift force tha t a particle, which is lying on a surface, experiences by the turbulen t flow over the surface. This lift force is one of the four force comp onents experienced by the particle which are-in addition to lift-weigh t, adhesion and drag force. Here we consider only very small particles that are completely embedded in the viscous sublayer of a turbulent b oundary layer. For the measurement of the lift force on these particle s no experimental technique was available. Therefore we have developed a new technique for measuring this lift force and its fluctuations. I t is capable of measuring fluctuating lift forces of around 10(-9) N. A particle is glued on top of a cantilever; a focused laser beam is us ed to measure the deflection of the cantilever. The experimental set-u p and the measurement technique are explained and some results are sho wn.