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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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96 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS2017

Optical Flow for Flight and Wind Tunnel Background Oriented Schlieren Imaging

Background oriented Schlieren images have historically been generated by calculating the observed pixel displacement between a wind-on and wind-o image pair using normalized cross-correlation. This work uses optical flow to solve the displacement fields which generate the Schlieren images. A well established method used in the computer vision community, optical flow is the apparent motion in an image sequence due to brightness changes. The regularization method of Horn and Schunck is used to create Schlieren images using two data sets: a supersonic jet plume shock interaction from the NASA Ames Unitary Plan Wind Tunnel, and a transonic flight test of a T-38 aircraft using a naturally occurring background, performed in conjunction with NASA Ames and Armstrong Research Centers. Results are presented and contrasted with those using normalized cross-correlation. The optical flow Schlieren images are found to provided significantly more detail. We apply the method to historical data sets to demonstrate the broad applicability and limitations of the technique.

Image processing↗
NASA NTRS2016

Background Oriented Schlieren (BOS) of a Supersonic Aircraft in Flight

This presentation describes the development and use of Background Oriented Schlieren (BOS) on a full-scale supersonic jet in flight. A series of flight tests was performed in October 2014 and February 2015 using the flora of the desert floor in the Supersonic Flight Corridor on the Edwards Air Force Base as a background. Flight planning was designed based on the camera resolution, the mean size and color of the predominant plants, and the navigation and coordination of two aircraft. Software used to process the image data was improved with additional utilities. The planning proved to be effective and the vast majority of the passes of the target aircraft were successfully recorded. Results were obtained that are the most detailed schlieren imagery of an aircraft in flight to date.

Visualization↗
NASA NTRSDate not supplied

PIV Measurements of Shock-Wave/Boundary-Layer Interactions at Mach 2.5 in a Circular Test Section

The particle image velocimetry (PIV) measurement technique has been applied to make detailed measurements in an impinging shock-wave/boundary-layer interaction (SWBLI) flowfield in a test section of circular cross-section. By virtue of this test section geometry, the flowfields studied are free from effects of the complex coupling of sidewall and corner interaction into the primary impinging shock interaction typical of a rectangular test section. The cone-cylinder shock generator hardware was arranged in both coaxial alignment with the test section to generate axisymmetric SWBLIs and in offset positions to generate swept SWBLIs. The angle of the conical section was also varied to alter the strength of the impinging shock wave. The application of the PIV technique in this test section required meticulous design to provide adequate optical access without disturbing the SWBLI flow. Details of the stereoscopic PIV apparatus and the velocity measurements obtained for a Mach 2.5 freestream are presented. Key features of the mean velocity and turbulent stress fields are highlighted. This data set should enable validation of computational fluid dynamics results for these flowfields.

Shockwave Boundary Layer Interaction↗
NASA NTRSDate not supplied

PIV Measurements of Shock-Wave/Boundary-Layer Interactions at Mach 2.5 in a Circular Test Section

The particle image velocimetry (PIV) measurement technique has been applied to make detailed measurements in an impinging shock-wave/boundary-layer interaction (SWBLI) flowfield in a test section of circular cross-section. By virtue of this test section geometry, the flowfields studied are free from effects of the complex coupling of sidewall and corner interaction into the primary impinging shock interaction typical of a rectangular test section. The cone-cylinder shock generator hardware was arranged in both coaxial alignment with the test section to generate axisymmetric SWBLIs and in offset positions to generate swept SWBLIs. The angle of the conical section was also varied to alter the strength of the impinging shock wave. The application of the PIV technique in this test section required meticulous design to provide adequate optical access without disturbing the SWBLI flow. Details of the stereoscopic PIV apparatus and the velocity measurements obtained for a Mach 2.5 freestream are presented. Key features of the mean velocity and turbulent stress fields are highlighted. This data set should enable validation of computational fluid dynamics results for these flowfields.

Shockwave Boundary Layer Interaction↗