DISK-LIKE BODY SAMPLING IN A TURBULENT WIND

In this paper a study is made of the sampling characteristics of a dis kshaped sampler facing a turbulent wind. The Reynolds-averaged Navier- Stokes equation and the k-epsilon turbulence model are used to predict the turbulent mean fluid motion past an axially symmetric disklike sa mpler, where the sampler is taken to have a single orifice on the side facing the oncoming flow. Based on the resulting velocity distributio n of the fluid flow, the equations of motion of the particle are trace d in order to obtain the particle trajectories which are then used to determine the aspiration efficiency of the sampler. The dependence of the aspiration efficiency on the five parameters, namely, the Stokes n umber St, the velocity ratio of the free stream speed to the suction s peed (U0/U(s), the ratio of the sampler diameter to the orifice diamet er (D0/D), the Reynolds number (Re) and the turbulence intensity (I) h as systematically been investigated. It is of interest to note that a comparison of the present results with the proposed impaction model re veals some interesting phenomena. Of all the theoretical predictions, the present computational results give the best agreement with all the available experimental data and this agreement is good. Thus the mode l may be extended to study the flow and particle characteristics for t hree-dimensional samplers.