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Passive Rocket Diffuser Testing: Reacting Flow Performance of Four Second-Throat GeometriesSecond-throat diffusers serve to isolate rocket engines from the effects of ambient back pressure. As one of the nation's largest rocket testing facilities, the performance and design limitations of diffusers are of great interest to NASA's Stennis Space Center. This paper describes a series of tests conducted on four diffuser configurations to better understand the effects of inlet geometry and throat area on starting behavior and boundary layer separation. The diffusers were tested for a duration of five seconds with a 1455-pound thrust, LO2/GH2 thruster to ensure they each reached aerodynamic steady state. The effects of a water spray ring at the diffuser exits and a water-cooled deflector plate were also evaluated. Static pressure and temperature measurements were taken at multiple axial locations along the diffusers, and Computational Fluid Dynamics (CFD) simulations were used as a tool to aid in the interpretation of data. The hot combustion products were confirmed to enable the diffuser start condition with tighter second throats than predicted by historical cold-flow data or the theoretical normal shock method. Both aerodynamic performance and heat transfer were found to increase with smaller diffuser throats. Spray ring and deflector cooling water had negligible impacts on diffuser boundary layer separation. CFD was found to accurately capture diffuser shock structures and full-flowing diffuser wall pressures, and the qualitative behavior of heat transfer. However, the ability to predict boundary layer separated flows was not consistent.
Document ID
20170001791
Acquisition Source
Stennis Space Center
Document Type
Technical Memorandum (TM)
Authors
Jones, Daniel R. (Stennis Space Center Bay Saint Louis, Mississippi, United States)
Allgood, Daniel C. (Stennis Space Center Bay Saint Louis, Mississippi, United States)
Saunders, Grady P. (Jacobs (United States) Dallas, Texas, United States)
Date Acquired
February 27, 2017
Publication Date
December 1, 2016
Subject Category
Spacecraft Design, Testing And Performance
Report/Patent Number
NASA/TM-2016-219221
Funding Number(s)
CONTRACT_GRANT: NNS07AB21C
Distribution Limits
Public
Copyright
Public Use Permitted.

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