Application of the DSMC Method for Design of a Coaxial Microthruster Nozzle
The Direct Simulation Monte Carlo (DSMC) method is used to numerically simulate and design a micronozzle with improved performance. Thrust calculations using the DSMC method demonstrate that the coaxial micronozzles can achieve milli-Newton thrust levels with specific impulses on the order of 45 s using argon in a cold gas expansion. Improved micronozzle designs of coaxial microthrusters are also proposed. Coaxial micronozzles utilizing center-body geometries to exploit pressure thrust show about 140% increase in specific impulse at low Reynolds numbers compared to a traditional converging nozzle.
Effects of wavy surface roughness on the performance of micronozzles
Recent trends in small-scale (~1 dm 3 ) satellites motivate the further development of microscale propulsion subsystems. In the present paper, we focus on flow dynamics simulations of conical convergent-divergent micronozzles and on the increased importance of wall effects due to the decrease in the characteristic length of such small systems. The inefficiency associated with viscous losses due to the developing boundary layer and the effect of sinusoidal surface roughness due to the employed microelectromechanical-system fabrication techniques are studied through computational fluid dynamics simulations for nonturbulent, nonrarefied flow conditions. Depending on the specific nature of the surface roughness, the formation and reflection of several weak shocks and, as a consequence, a decreased performance are observed. © 2010 by the American Institute of Aeronautics and Astronautics, Inc.
ANNULAR INTERNAL-EXTERNAL-EXPANSION ROCKET NOZZLES FOR LARGE BOOSTER APPLICATIONS
For large-thrust booster applications, annular rocket nozzles employing both internal and external expansion are investigated. In these nozzles, free-stream air flows through the center as well as around the outside of the exiting jet. Flaps for deflecting the rocket exhaust are incorporated on the external-expansion surface for thrust-vector control. In order to define nozzle off-design performance, thrust vectoring effectiveness, and external stream effects, an experimental investigation was conducted on two annular nozzles with area ratios of 15 and 25 at Mach 0, 2, and 3 in the Lewis 10- by 10-foot wind tunnel. Air, pressurized to 600 pounds per square inch absolute, was used to simulate the exhaust flow. For a nozzle-pressure-ratio range of 40 to 1000, the ratio of actual to ideal thrust was essentially constant at 0.98 for both nozzles. Compared with conventional convergent-divergent configurations on hypothetical boost missions, the performance gains of the annular nozzle could yield significant orbital payload increases (possibly 8 to 17 percent). A single flap on the external-expansion surface of the area-ratio-25 annular nozzle produced a side force equal to 4 percent of the axial force with no measurable loss in axial thrust.