Measurements and Computations of Second-Mode Instability Waves in Three Hypersonic Wind Tunnels

High-frequency pressure-fluctuation measurements were made in AEDC Tunnel 9 at Mach 10 and the NASA Langley 15-Inch Mach 6 and 31-Inch Mach 10 tunnels. Measurements were made on a 7deg-half-angle cone model. Pitot measurements of freestream pressure fluctuations were also made in Tunnel 9 and the Langley Mach-6 tunnel. For the first time, second-mode waves were measured in all of these tunnels, using 1-MHz-response pressure sensors. In Tunnel 9, second-mode waves could be seen in power spectra computed from records as short as 80 micro-s. The second-mode wave amplitudes were observed to saturate and then begin to decrease in the Langley tunnels, indicating wave breakdown. Breakdown was estimated to occur near N approx. equals 5 in the Langley Mach-10 tunnel. The unit-Reynolds-number variations in the data from Tunnel 9 were too large to see the same processes. In Tunnel 9, the measured transition locations were found to be at N = 4.5 using thermocouples, and N = 5.3 using 50-kHz-response pressure sensors. What appears to be a very long transitional region was observed at a unit Reynolds number of 13.5 million per meter in Tunnel 9. These results were consistent with the high-frequency pressure fluctuation measurements. High-frequency pressure fluctuation measurements indicated that transition did occur in the Langley Mach-6 tunnel, but the location of transition was not precisely determined. Unit Reynolds numbers in the Langley Mach-10 tunnel were too low to observe transition. More analysis of this data set is expected in the future

Surface Measurements of a Supersonic Jet in Subsonic Compressible Crossflow for the Validation of Computational Models

Despite many decades of jet-in-crossflow experimentation, a distinct lack of data remains for a supersonic jet exhausting into a subsonic compressible crossflow. The present investigation seeks to address this deficiency by examining the flowfield structure of a Mach 3.73 jet injected transversely from a flat plate into a subsonic compressible freestream. The experimental results described herein include the mean surface pressure field as mapped using static pressure taps on the flat plate and an identification of flow features by employing an oil-based surface flow tracer. The possibility of flow separation within the nozzle itself also is addressed using pressure taps along the nozzle interior wall, as is the asymmetry of the separation line due to the variation of the local backpressure around the perimeter of the nozzle orifice resulting from the jet-in-crossflow interaction. Pressure data both on the flat plate and within the nozzle are presented at numerous angles with respect to the crossflow freestream direction to provide a breadth of measurements throughout the interaction region. Since the data are intended for use in validating computational models, attention is paid to providing details regarding the experimental geometry, boundary conditions, flowfield nonuniformities, and uncertainty analyses. Eight different sets of data are provided, covering a range of values of the jet-to-freestream dynamic pressure ratio from 2.8 to 16.9 and a freestream Mach number range of 0.5 to 0.8

Validation of Multi-Frame PIV Image Interrogation Algorithms in the Spectral Domain

Multi-frame correlation algorithms for time-resolved PIV have been shown in previous studies to reduce noise and error levels in comparison with conventional two-frame correlations. However, none of these prior efforts tested the accuracy of the algorithms in spectral space. Even should a multi-frame algorithm reduce the error of vector computations summed over an entire data set, this does not imply that these improvements are observed at all frequencies. The present study examines the accuracy of velocity spectra in comparison with simultaneous hot-wire data. Results indicate that the high-frequency content of the spectrum is very sensitive to choice of the interrogation algorithm and may not return an accurate response. A top-hat-weighted sliding sum-of-correlation is contaminated by high-frequency ringing whereas Gaussian weighting is indistinguishable from a low-pass filtering effect. Some evidence suggests the pyramid correlation modestly increases bandwidth of the measurement at high frequencies. The apparent benefits of multi-frame interrogation algorithms may be limited in their ability to reveal additional spectral content of the flow.Virtual/online event due to COVID-19Aerodynamic

Innovative Measurement Diagnostics for Analysis of Jet Interactions in Rotating Flowfields

The present document summarizes the experimental efforts of a three-year study funded under the Laboratory Directed Research and Development program of Sandia National Laboratories. The Innovative Diagnostics LDRD project was designed to develop new measurement capabilities to examine the interaction of a propulsive spin jet in a transonic freestream for a model in a wind tunnel. The project motivation was the type of jet/fin interactions commonly occurring during deployment of weapon systems. In particular, the two phenomena of interest were the interaction of the propulsive spin jet with the freestream in the vicinity of the nozzle and the impact of the spin rocket plume and its vortices on the downstream fins. The main thrust of the technical developments was to incorporate small-size, Lagrangian sensors for pressure and roll-rate on a scale model and include data acquisition, transmission, and power circuitry onboard. FY01 was the final year of the three-year LDRD project and the team accomplished much of the project goals including use of micron-scale pressure sensors, an onboard telemetry system for data acquisition and transfer, onboard jet exhaust, and roll-rate measurements. A new wind tunnel model was designed, fabricated, and tested for the program which incorporated the ability to house multiple MEMS-based pressure sensors, interchangeable vehicle fins with pressure instrumentation, an onboard multiple-channel telemetry data package, and a high-pressure jet exhaust simulating a spin rocket motor plume. Experiments were conducted for a variety of MEMS-based pressure sensors to determine performance and sensitivity in order to select pressure transducers for use. The data acquisition and analysis path was most successful by using multiple, 16-channel data processors with telemetry capability to a receiver outside the wind tunnel. The development of the various instrumentation paths led to the fabrication and installation of a new wind tunnel model for baseline non-rotating experiments to validate the durability of the technologies and techniques. The program successfully investigated a wide variety of instrumentation and experimental techniques and ended with basic experiments for a non-rotating model with jet-on with the onboard jets operating and both rotating and non-rotating model conditions