Computed vs. Measured Force Coefficients in a Small Arc Facility

Measurements of the aerodynamic forces acting on a 70◦ semiangle cone have been made in the small arc facility SPES at the Department of Aerospace Engineering in Naples. Two sets of measurements, with arc electrical currents of 300 and 400 A, respectively, are noted; the test gas was argon, the mass flow rate was 1 g/s. Because of the existing difficulties in measuring the free stream parameters in an arc wind tunnel, two procedures are proposed to calculate them: the first based on the one-dimensional theory and the second solving the flow field in the nozzle by a two-dimensional direct simulation Monte Carlo method (DSMC) code; the ‘continuum break-down limit’ is overcome just before the exit of the nozzle. The experimental force coefficients have been compared both with other experimental data available in the open literature and with the results from three-dimensional DSMC code. The comparison shows, as expected, some discrepancies among experimental and numerical data due to the uncertainties in the test parameters and to the interference, at high angle of attack, of the sting supporting the model.