We have investigated the lift force on a small isolated particle which is attached to a flat smooth surface and embedded within the viscous sublayer of the turbulent boundary layer over this surface. We have developed a novel experimental technique with which it is possible to measure both the mean and fluctuating lift force by gluing the particle on top of a silicium cantilever. The deflection of this cantilever is measured with a focused laser beam. The sensitivity of the focus detection system allows us to measure a lift force with an average value around 10−8N and with a standard deviation of approximately 5% of the mean. This means that our device is at least a factor of 100 more sensitive than previous devices and at the same time able to measure the lift forces on smaller particles. Data for the mean lift force (FL+) as a function of the particle radius (a+), where both parameters have been non-dimensionalized with the kinematic viscosity v and the friction velocity u*, are obtained in the range 0.3 < a+ < 2. The data support the relationship: FL+ = (56.9 ± 1.1) (a+)1.87±0.04. Also results on the fluctuating lift force have been obtained. We find that the ratio of the r.m.s. to the mean lift force is approximately 2.8.

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The entrainment or resuspension of particles in air or water is a very common phenomenon. It is determined by the fluctuating lift force that a panicle, which is lying on a surface, experiences by the turbulent flow over the surface.This lift force is one of the four force components experienced by the particle which are-in addition to lift-weight, adhesion and drag force. Here we consider only very small particles that are completely embedded in the viscous sublayer of a turbulent boundary layer. For the measurementof the lift force on these particles no experimental technique was available. Therefore we have developed a new technique for measuring this lift force and its fluctuations. It is capable of measuring fluctuating lift forces of around N. A particle is glued on top of a cantilever: a focused laser beam is used to measure the deflection of the cantilever. The experimental set-uD and the measurement technique are explained and some results are shown.

In the literature field experiments were performed in which factors affecting the resuspension of particulate material by road traffic were investigated. The factors involved were in most cases the particle size and the speed of the car. In some cases even the size of the car was varied (medium-sized car or truck). The present experiments were made to obtain a better understanding of the influence of the aerodynamic effects (not the tire effects) affecting resuspension by road traffic. In the experiments a model was used to investigate the influence of its shape, its velocity, and its distance to the surface. The experiments also included the size of the particles and the kind of surface from which the particles were resnspended. These experiments were performed in order to make possible a better interpretation of the field tests.