Experimental and numerical investigations of low-density nozzle and plume flows of nitrogen

Abstract

Experimental and numerical investigations are performed and compared for the flow of nitrogen in a small nozzle and in the near field of the plume resulting from expansion into near-vacuum conditions. The experimental data obtained were in the form of pressure measurements using a pitot tube, in the nozzle-exit plane and near field of the plume. Since the flow regimes vary from continuum, at the nozzle throat, to rarefied, in the plume, two different numerical studies are undertaken: the first employs a continuum approach in solving the Navier-Stokes equations, and the second employs a stochastic particle approach through the use of the direct simulation Monte Carlo (DSMC) method. Comparison of the experimental data and the numerical results at the nozzle exit reveals that the DSMC technique provides the more accurate description of the expanding flow. It is discovered that the DSMC solutions are quite sensitive to the model employed to simulate the interaction between the gas and the nozzle-wall surface. It is concluded that the simple fully diffuse model is quite satisfactory for the present application. The study provides the strongest evidence to date that the DSMC technique predicts accurately the flow characteristics of low-density expanding flows.Nomenclature D e = diameter at nozzle exit D p = diameter of probe D t = diameter at nozzle throat M x -Mach number ahead of a shock P x = static pressure ahead of a shock P 0 = total pressure P oy = total pressure behind a shock P x = static pressure ahead of a shock Re p -probe Reynolds number T 0 -total temperature r ref = reference temperature T w = temperature of nozzle wall T x = static temperature ahead of a shock T y = static temperature behind a shock U 0 = thermal velocity at total temperature t/oo = freestream velocity 7 = ratio of specific heats jLt ref = viscosity given by reference temperature H y = viscosity given by temperature behind a shock a?= viscosity temperature exponent Poo = freestream density

Hybrid simulations of rarefied supersonic gas flows in micro-nozzles

“…In the transition regime, the most accurate method to use is Direct Simulation Monte Carlo (DSMC) [13], which was shown to provide accurate solutions for highly rarefied nozzle and plume flows first in [14]. DSMC is more efficient than deterministic molecular models such as Molecular Dynamics (MD), and more flexible and generally applicable than methods based on direct solution of the Boltzmann or BGK equations [10].…”

Scalar and Parallel Optimized Implementation of the Direct Simulation Monte Carlo Method

“…At the beginning of the [17]. They are difficult to calculate since they require the slope the flow separates.…”

Study of the effects of preheated wall/plates in microthruster systems

“…Then numerical methods were proposed by Rae (1971) and Boyd et al (1992) in order to investigate converging-diverging nozzles numerically. Boyd used a DSMC method and proved that this method was accurate enough to analyze the flow especially in the expanding section of the thruster with a near vacuum exit boundary conditions.…”