Drag on a flat plate in low-Reynolds-number gas flows

Airflow over a flat plate at zero incidence is investigated as a function of the Reynolds number Re and the Mach number M under subsonic, low-Reynolds-number conditions. The flows are simulated using the direct simulation Monte Carlo (DSMC) method and the information preservation (IP) method that is a modified DSMC method developed for low-speed rarefied gas flows. Good agreement is obtained between the DSMC and IP results and between the IP results and available experimental data. The simulations predict that the drag coefficient on the flat plate depends on the Reynolds number and the Mach number, and both the rarefied and compressible effects on the drag coefficient increase when the flow Reynolds number decreases. It is found that the normalized drag [C.sub.D] * M depends on [square root of](Re)/[M.sup.0.8] when this parameter varies between 1 and 100, which suggests a scaling law for engineering analysis.