Mixing pressure-rise parameter for effect of nozzle geometry in diffuser-ejectors

Nicholas, T. M. T.; Narayanan, Anil K.; Muthunayagam, A.E.

doi:10.2514/3.24049

Cited by 12 publications

(1 citation statement)

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“…The starting stagnation pressure for a diffuser is a function of both the geometrical parameters (such as the nozzle area ratio, diffuser contraction angle, and the second-throat L=D ratio [13][14][15][16]) and the operating conditions of the motor. The pumping performance of the ejector-diffuser has been observed to be sensitively dependent on the attachment of primary flow on the inner wall of the duct [17].…”

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Performance Evaluation of Second-Throat Diffuser for High-Altitude-Test Facility

Kumaran

Sundararajan

Manohar

2010

Journal of Propulsion and Power

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The performance of a second-throat ejector-diffuser system employed in high-altitude testing of large-area-ratio rocket motors is considered under various steady and transient operating conditions. When the diffuser attains started condition, supersonic flow fills the entire inlet section and a series of oblique shock cells occurring in the diffuser duct seal the vacuum environment of the test chamber against backflow. The most sensitive parameter that influences the stagnation pressure needed for diffuser starting is the second-throat diameter. Between the throat and exit diameters of the nozzle, there exists a second-throat diameter value that corresponds to the lowest stagnation pressure for starting. When large radial/axial gaps exist between the nozzle exit and diffuser duct, significant reverse flow occurs for the unstarted cases, which spoils the vacuum in the test chamber. However, the starting stagnationpressure value remains unaffected by the axial/radial gap. Numerical simulations establish that it is possible to arrive at an optimum diffuser geometry that facilitates early functioning of the high-altitude-test facility during motor ignition phase. The predicted axial variations of static pressure and temperature along the diffuser for the testing of a cryogenic upper-stage motor agree well with available experimental data. Nomenclature= diffuser exit diameter e = specific internal energy G v = rate of production of turbulent viscosity k = thermal conductivity L = length in axial direction L 1 = entry duct length L 2 = convergent duct length L 3 = second-throat length L 4 = divergent duct length M = Mach number M i = area-averaged diffuser inlet Mach number P o = stagnation pressure p = static pressure p e = diffuser backpressure p v = vacuum pressure in the test chamber q = heat transfer per unit area r = radial coordinate T = static temperature T o = stagnation temperature t = time v = velocity Y v = rate of destruction of turbulent viscosity z = axial coordinate r = radial gap z = axial gap = convergence angle = absolute viscosity = density rr = normal stress in radial direction zr , rz = tangential stresses zz = normal stress in axial direction = hoop stress = viscous dissipation function Subscripts l = laminar r = radial t = turbulent z = axial

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