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Nonintrusive diagnostics are often sought to provide information on combustion exhaust flows due to the harsh environment of the flow. Laserinduced fluorescence (LIF) is one technique in which a chosen flow molecule or marker is probed to yield gross flow properties such as static temperature and flow velocities. The work presented herein describes application of LIF to the combustion exhausts of two full-scale liquid-propellant rocket engines, i.e., the Space Shuttle Orbital Maneuvering System (OMS) and the Titan secondstage LR91 rocket engines, as they undergo routine testing in simulated altitude test cells. The method is based upon the use of cw ring-dye lasers which scan in frequency over either the Na DI or D2 line at 5896 and 5890 A. Na is used as a basis for this approach since it occurs as a trace element in both hydrogen and amine rocket fuels. The generic apparatus is described, including a discussion of the collection and interpretation of the LIF signal to yield radial and temporal profiles of radial flow velocity and static temperature. CFD modeling of the plumes was used to provide baseline estimates of the exhaust flow properties. It was found that the CFD model does a fairly good job of predicting the gross behavior of the flow, although some items of fine spatial structure are not reproduced well. The OMS and LR91 rocket engine nozzles are drastically different in construction and cooling method. It was found that excellent LIF results were obtained with the radiation-cooled nozzle (OMS), while the fuel-film cooling (FFC) used for the LR91 nozzle generated an optically thick and particle-laden region which severely impeded the determination of static temperature from the Na LIF measure* The research reported herein was performed by the Arnold Engineering Development Center (AEDC), Air Force Materiel Command. Work and analysis for this research were performed by personnel of Sverdrup Technology, Inc., AEDC Group, technical services contractor for AEDC. Further reproduction is authorized to satisfy needs of the U. S. Government. |
