Particle image velocimetry (PIV) was successfully used to capture the evolution of steady and unsteady exhaust flows from test hardware operated within several facilities at the NASA Glenn Research Center. In the Small Hot Jet Acoustic Rig at Glennís AeroAcoustic Propulsion Laboratory, the flows from numerous exhaust nozzles equipped with chevrons, or serrated edges, which are being investigated as passive jet-noise-reduction devices, were examined to evaluate their mixing performance. In a test cell at Glennís Rocket Laboratory, the exhaust flows from a pulse detonation engine (PDE) and an ejector coupled downstream of a PDE, being investigated as a noise-reduction and thrust-augmentation device for hybrid propulsion applications, were examined to evaluate their phase-averaged cyclic operating behavior. PIV is uniquely advantageous in these situations because of its ability to produce detailed and highly accurate complete flow-field exhaust velocity vector maps. In addition, the use of PIV significantly reduces facility test times over conventional measurement techniques incorporating intrusive diagnostic probes.
Mean velocity fields evaluated from stereoscopic PIV data at several measurement stations downstream of chevron nozzles. Left: Axial plane. Right: Cross plane.
Stereoscopic PIV, having become a well-established technique for the measurement of the three components of velocity within a fluid plane, was successfully used to characterize the exhaust flow fields from a parametric test matrix of 16 chevron and 2 baseline circular 50.8-mm-diameter nozzles. During nozzle jet operation, acoustic mach numbers ranged from 0.9 to 1.5 and static temperature ratios ranged from 0.84 to 2.7. Detailed surveys of the single jet flows were performed to capture three-dimensional features of the turbulent exhaust jet evolution. Cross-flow planar measurements were obtained at 12 locations, ranging from 0.1 to 20 nozzle diameters d downstream of the nozzle exit planes. Streamwise measurements, along the jet centerlines, were obtained at 10 partially overlapping downstream locations, providing complete axial surveys over a region extending beyond 20 nozzle diameters downstream of the nozzle exit planes. In both optical configurations, the measurement planes were sized to completely capture the fully turbulent jet shear layer growth. The measured three-dimensional mean and turbulent velocity fields, along with computed second-order statistics including axial vorticity and turbulent kinetic energy, were evaluated for all test points. Well-defined streamwise vortex structures in the jet shear layers were measured and documented.
Sample ensemble-averaged exhaust flow fields measured two jet diameters, d, downstream of exit plane of several chevron nozzles (with different chevron configurations). In-plane velocities are shown as vectors, with the out-of-plane velocity component shown as contours of constant color.
Ensemble-averaged exhaust flow fields measured at several phase-locked time steps during a PDE operating cycle. Top row: In-plane velocity vector fields overlaid onto contours of constant vorticity for direct exhaust from the PDE. Bottom row: In-plane velocity vector fields overlaid onto contours of constant vorticity for detonation-driven ejector exhaust.
An initial series of planar PIV measurements were successfully performed using the small detonation facility in Glennsí Rocket Lab Test Cell 31 to provide quantitative insight into the mechanisms of thrust augmentation using PDE-coupled ejectors. The data are believed to be the first quantitative PIV measurements made on the exhaust flow field of an operational PDE and include the measurement of the driven exhaust flow out of an ejector placed downstream of the PDE. An examination of the planar PIV velocity data revealed the presence of a highly repeatable, strong emitted vortex with each firing (pulse) of the engine. The peak diameter of the vortex leaving the PDE is very nearly the same as the diameter of the ejector used in this study, which yielded the highest thrust augmentation measured in previous testing. This result is consistent with other unsteady thrust augmentation studies and confirms that the emitted vortex associated with all unsteady thrust augmentation devices plays a central role in the high levels of thrust augmentation observed. Continued analysis of the PIV data is in progress and is expected to provide a validation benchmark for computational solutions of PDE, PDE-driven ejector, and exhaust flow fields, as well as providing insights into determining optimal ejector configurations.
Experimental arrangement and measurement regions of interest for planar PIV exhaust flow measurements along the centerline axial exhaust from the PDE and the detonation-driven ejector. Shown are velocity vector maps overlaid onto contours of constant velocity at several phase steps during engine operation. The flow is from left to right.
Opalski, A.; Wernet, M.; and Bridges, J.: Chevron Nozzle Performance Characterization Using Stereoscopic DPIV. AIAA-2005-0444, 2005.
Opalski, A.; Paxson, D.; and Wernet, M.: Detonation Driven Ejector Exhaust Flow Characterization Using Planar DPIV. AIAA-2005-4379, 2005.
Find out more about the research of Glennís Optical Instrumentation Technology Branch: http://www.grc.nasa.gov/WWW/OptInstr/
QSS Group, Inc., contact:
Dr. Anthony B. Opalski, 216-433-3908, Anthony.B.Opalski@nasa.gov
Glenn contact: Dr. Mark P. Wernet, 216-433-3752, Mark.P.Wernet@nasa.gov
Authors: Dr. Anthony B. Opalski, Dr. Mark P. Wernet, Dr. Daniel E. Paxson, and Dr. James E. Bridges
Headquarters program office: Aeronautics Research
Programs/Projects: QAT, CVCCE
Last updated: October 16, 2006
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