MHz Rate Imaging of Boundary Layer Transition on Elliptic Cones

The Gas Dynamics Lab at Princeton University is currently taking part in transition studies on elliptic cone models. Working with the Applied Physics Group, some of the most recent laser diagnostics for hypersonic flow are being utilized to produce previously unobtainable views of the boundary layer. A "pulse-burst" Nd:YAG laser system has been developed by Pingfan Wu which allows repetition rates up to 1 MHz. A high-speed prototype camera developed by Princeton Scientific Instruments is able to capture a 30-image "movie" of the flow.

Filtered Rayleigh Scattering (FRS) has been used to image turbulent structure on flat-plate boundary layers and is now being applied to studies of the transitional boundary layer over elliptic cones at Mach 8.0. The flow is seeded with carbon dioxide which condenses in the freestream and enhances the Rayleigh signal. In the images which follow, the light regions represent the cold, high-density freestream while the dark regions represent the low-density boundary layer (where sublimation of the carbon dioxide crystals has ocurred due to aerodynamic heating). The research is being carried out by Mark Huntley, under the direction of Professor A.J. Smits.

Two elliptic cone configurations are being tested. The first has 2:1 cross section with a half-angle along the major axis of 13.8 degrees. It is the first 0.1524 m section of the 1.016 m cone which was tested in AEDC Tunnel B by Roger Kimmel and Jon Poggie of Wright Laboratory. Previous results on the 2:1 configuration include numerical computations, hot-film probes, schlieren, shadowgraphs and oill flow. FRS images were then taken in the Princeton Mach 8 facility. The second model is a 0.2416 m 4:1 elliptic cone with 17.5 degree half-angle on the major axis. FRS images were also taken on a flat plate model.

The boundary layer was imaged using streamwise (X-Y), spanwise (Y-Z), and planform (X-Z) laser sheet orientations.

Representative single-shot FRS images of centerline (minor axis) region along 4:1 elliptic cone. Image scaling varies. (Rex=2.6E6 for all images)

Filtered Rayleigh Scattering images on the 4:1 elliptic cone:

Single-shot streamwise images of the boundary layer (34K JPEG image)
Single-shot spanwise images of the boundary layer (43K JPEG image)

Motion pictures and 3D images of the 4:1 cone produced using pulse-burst laser system.

Filtered Rayleigh Scattering images on the 2:1 elliptic cone:

Motion pictures and 3D images of the 2:1 cone.

Filtered Rayleigh Scattering images on the Flat Plate:

Motion pictures and 3D images of the flate plate.

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