Pitot pressure and heat-transfer measurements in hydrazine thruster plumes

Abstract

Pitot pressure and heat-transfer measurements have been made in plumes of 0.5-N (conical nozzle), 2-N, and 5-N (contoured nozzles) monopropellant hydrazine thrusters. The main objectives are to check the DFVLR simple plume model and to determine reliable model input values for real thrusters. The methods used for the heattransfer measurements (applying a sphere probe), the recovery temperature determination, and the evaluation of the plume quantities relevant for plume impingement calculations are outlined. The Pitot pressure measurements showed the existence of shock disturbances in the near plume flowfield of the contoured nozzles. Stagnation temperatures between 900 and 1350 K were deduced from the measured recovery temperatures. The corresponding molecular weight range was found to be between 11 and 14.5 and the most reasonable mean effective ratio of specific heats to be K = 1.4 ±0.03 for the expansion from the stagnation chamber to the continuum plume flow. This value is proposed for simple plume model calculations. The model heat-transfer results agree well with the experiments. Nomenclaturespecific heat at constant pressure and volume, respectively d = diameter F = thrust 7 sp = specific impulse 7 sp = F/m m -mass M = molecular weight Ma = Mach number p = pressure Pr = Prandtl number <2 = heat transfer r = radius r = recovery factor, Eq. (7) R = specific gas constant Re 2 = Reynolds number, Eq. (19) St = Stanton number, Eq. (6) t = time T = temperature u = velocity x = centerline distance from nozzle exit X l = dissociation degree of NH 3 d" = momentum thickness 6 E = nozzle exit angle AC = ratio of specific heats, K = C P /C V JLI = viscosity p = density Subscripts BL = boundary-layer (continuum) theory cond = conduction E = nozzle exit condition FM = free molecule K = in the vacuum chamber lim = limiting condition for Mo-oo loss = losses by radiation and conduction off, on = thruster not firing and firing, respectively r = at recovery condition rad = radiation s = sphere u = velocity w =at the wall, sphere probe condition 0 = stagnation condition 1 = freestream 2 = condition behind a normal shock wave Superscripts 1,2,... = number of iteration ( )* = nozzle throat ( ) =time derivative IntroductionI N a previous study, existing analytical plume flow models 1 " 3 were extended to deliver all flow quantities relevant to impingement calculations. Free-molecular plume flow was included by the definition of a freezing surface. 4 ' 5 In this DFVLR model, constant composition flow is assumed with mean constant gas properties. The angular plume flow description is most sensitive to changes in the ratio of specific heats of the exhaust gases.The present work is part of an extensive study of plume flow and impingement effects on spacecraft surfaces, that serves to test, verify, and improve the model by analyzing systematically the influence of the thruster nozzle geometry, nozzle boundary layer, and ratio of specific heats using pure gases. 6 This paper deals with experiments in real hydrazine plume flows from thr...

Numerical comparison of exhaust plume flow behaviors of small monopropellant and bipropellant thrusters

“…In case of hydrazine, thrust is provided by the catalytic decomposition and the final combustion product gases consist of three main species, H 2 , N 2 , and NH 3 following overall chemical equilibrium process in Eq 8 [ 11 , 17 ]. where f represents for the extent of ammonia dissociation at given temperature [ 11 , 17 ]…”

Plume impingement investigation using Monte-Carlo computations

“…The measurements conducted in plumes of an MBB/ ERNO 0.5 N conical nozzle were used to validate the present computer code developed by the aforementioned theoretical formulation [5,9]. At the axial location of 32 nozzle exit radii with the stagnation pressure of 15.7 bar and the stagnation temperature of 897 8C, Fig.…”

“…The gas properties of plume flows are determined by the subsequent overall hydrazine decomposition process occurred in the catalytic reaction chamber [9]…”

“…As the outflow is supersonic, no special consideration is needed and all flow variables are extrapolated from interior values. From references [2,9], the corresponding dissociation amount w in equation ( 6) is equal to 0.61. Thus, the gas species of the reaction product gas in exhaust plumes comprise hydrogen, nitrogen, and ammonia with the mass fraction of Y H 2 ¼ 0.076, Y N 2 ¼ 0.649, and Y NH 2 ¼ 0.275.…”

Determination of plume impingement disturbance characteristics for the ROCSAT-1 satellite

“…In addition, measurements of pitot pressure and aerodynamic heat¯ux in the vacuum condition were conducted to explore plumes and plume interactions of M BB/ER N O 0.5 N (conical nozzle), 2 N and 5 N (contoured nozzles) hydrazine thrusters. The development process from the shock waves in a nozzle to plume¯ow expansion was well elucidated [27,28]. The aforementioned measured results have established an extensive database on plume ®eld properties as well as impingement pressure and heat¯ux giving increasing con®dence in the plume¯ow predictions.…”