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Wind tunnel modifications consisting of the introduction of new turning vanes, baffles, diffuser, and test section were completed in 2019. Wind tunnel characterization best practices require a full characterization test entry following any of these modifications.
Within the past decade, a measurement uncertainty analysis (MUA) team was assembled at the NASA Glenn Research Center to assist the wind tunnel characterization team with quantification of uncertainty estimates for variables of interest in wind tunnels and test cells across the center. The initial analysis performed by the team was conducted on the 8- by 6- Foot Supersonic Wind Tunnel using results from the 1996/97 full calibration test entry. These MUA results were published in 2016 which included recommendations for methods to improve the uncertainty estimates for various variables of interest, such as changes to regression models, tunnel operation philosophy, and instrumentation choices. The wind tunnel characterization team utilized the proposed methods in 2019 during a full characterization test entry. Following publication of the 2019 test section characterization results, the MUA team pursued an update to the uncertainty estimates for the facility, which validated previous recommendations and revealed significantly reduced systematic uncertainties across most variables of interest. Inclusion of within-test repeat points in the 2019 test entry allowed for higher fidelity estimates of random uncertainty to be generated, as well. This collaboration between the facility, wind tunnel characterization, and MUA teams serves as an example of the data quality benefits that can be achieved through rigorous analysis of the sources of uncertainty in a ground-test facility.
Within the past decade, a measurement uncertainty analysis (MUA) team was assembled at NASA Glenn Research Center to assist the wind tunnel characterization team with quantification of uncertainty estimates for variables of interest in wind tunnels and test cells across the center. The initial analysis performed by the team was conducted on the 8- by 6-Foot Supersonic Wind Tunnel using results from the 1996/97 full calibration test entry. These MUA results were published in 2016 which included recommendations for methods to improve the uncertainty estimates for various variables of interest, such as changes to regression models, tunnel operation philosophy, and instrumentation choices. The wind tunnel characterization team utilized the proposed methods in 2019 during a full characterization test entry. Following publication of the 2019 test section characterization results, the MUA team pursued an update to the uncertainty estimates for the facility, which validated previous recommendations and revealed significantly reduced systematic uncertainties across most variables of interest. Inclusion of within-test repeat points in the 2019 test entry allowed for higher fidelity estimates of random uncertainty to be generated, as well. This collaboration between the facility, wind tunnel characterization, and MUA teams serves as an example of the data quality benefits that can be achieved through rigorous analysis of the sources of uncertainty in a ground-test facility.
NASA Glenn Research Center and Lockheed Martin tested an aircraft model in two wind tunnels to compare low-speed (subsonic) flow characteristics. Test objectives were to determine and document similarities and uniqueness of the tunnels and to verify that the 10- by 10-Foot Supersonic Wind Tunnel (10x10 SWT) is a viable low-speed test facility when compared to the 8- by 6-Foot Supersonic Wind Tunnel (8x6 SWT). Conclusions are that the data from the two facilities compares very favorably and that the 10-by 10-Foot Supersonic Wind Tunnel at NASA Glenn Research Center is a viable low-speed wind tunnel.
A brief history of the 8x6 Supersonic Wind Tunnel (SWT) and 9x15 Low Speed Wind Tunnel (LSWT) at NASA Glenn Research Center, Cleveland, Ohio is presented along with current capabilities and plans for future upgrades within the facility.
Supersonic inlets with external compression, having a good level performance at the critical operating point, exhibit a marked instability of the flow in some subcritical operation below a critical value of the capture mass flow ratio. This takes the form of severe oscillations of the shock system, commonly known as "buzz". The underlying purpose of this study is to indicate how Detached Eddy Simulation (DES) analysis of supersonic inlets will alter how we envision unsteady inlet aerodynamics, particularly inlet buzz. Presented in this paper is a discussion regarding the physical explanation underlying inlet buzz as indicated by DES analysis. It is the normal shock wave boundary layer separation along the spike surface which reduces the capture mass flow that is the controlling mechanism which determines the onset of inlet buzz, and it is the aerodynamic characteristics of a choked nozzle that provide the feedback mechanism that sustains the buzz cycle by imposing a fixed mean corrected inlet weight flow. Comparisons between the DES analysis of the Lockheed Martin Corporation (LMCO) N+2 inlet and schlieren photographs taken during the test of the Gulfstream Large Scale Low Boom (LSLB) inlet in the NASA 8x6 ft. Supersonic Wind Tunnel (SWT) show a strong similarity both in turbulent flow field structure and shock wave formation during the buzz cycle. This demonstrates the value of DES analysis for the design and understanding of supersonic inlets.
Recent customer requirements for improved Mach number stability for sonic boom signature measurements has piqued interest in the use of the solid-wall supersonic test section in the NASA Glenn Research Center 8- by 6-Foot Supersonic Wind Tunnel. To supply customers with understanding of the operating conditions and flow quality in this region of the tunnel, characterization tests were performed in the solid-wall supersonic test section in January 2020. The test entry covered the operating range of the facility for three-drive-motor operation. Calibration models were generated along with an improved understanding of operational considerations for this region of the tunnel. The data set acquired included centerline axial and planar flow-field distributions to quantify test section flow quality. The collected data provided an improved understanding of operational considerations for this region of the tunnel as well as allowed for the development of detailed calibration models for the solid-wall supersonic test section.