# Hypersonic boundary-layer separation detection with pressure-sensitive paint for a cone at high angle of attack

## Abstract

A measurement technique for identifying lee-side crossflow-induced boundary-layer separation on a blunt \(7^{\circ }\) half-angle circular cone at high angle of attack has been developed and tested. Previous work has shown that local minima in root-mean-squared (rms) pressure fluctuations on the surface are good identifiers of separation. These surface pressure fluctuations are measured with a temperature-corrected, high-frequency-response anodized-aluminum pressure-sensitive paint (AA-PSP). This AA-PSP was made in-house to provide the high frequency response required for this work. The sensor’s frequency response of 3 kHz proved to be fast enough to detect lines of local minimum rms pressure fluctuations indicative of separation on the lee side of the cone for angles of attack from \(9.8^{\circ }\) to \(15.8^{\circ }\). A shift in the separation location towards the windward side of the model was observed as angle of attack increased; however, the separation location converged to a constant azimuth for angles of attack greater than or equal to \(1.8\times\) the cone’s half angle.

## List of symbols

*I*Paint intensity (counts)

*M*Mach number

*p*Pressure (kPa)

*Re*Unit Reynolds number (/m)

*T*Temperature (K)

*w*Uncertainty (%)

*x*Streamwise distance(\(x=0\) at the model tip) (mm)

*y*Spanwise distance (\(y=0\) on the model centerline) (mm)

- \(\alpha\)
Angle of attack (\(^{\circ }\))

- \(\theta\)
Cone half angle (\(^{\circ }\))

- \(\varPhi\)
Gas concentration (\(\%\))

- \(\phi\)
Azimuth (\(\phi =0^{\circ }\) along windward ray) (\(^{\circ }\))

## Sub/superscripts

- cal
Value based on calibration

- cam
Value based on camera

- ref
Reference condition

- rms
Root-mean-squared fluctuation

- temp
Value based on temperature dependence

- total
Total value

- uni
Value based on uniformity

*x*Value based on streamwise distance

- 0
Stagnation condition

- −
Mean component

- \('\)
Fluctuating component

- \(\infty\)
Freestream condition

## Notes

### Acknowledgements

The authors would like to thank Prof. Sergey Leonov and Prof. Seong-Kyun Im for allowing access to their jointly operated ACT-1 wind-tunnel facility. In addition, thanks goes out to Notre Dame undergraduate research assistants E. Farnan and Michael Thompson for their work investigating anodization techniques and developing the image mapping technique, respectively. Notre Dame graduate research assistants Harrison Yates and Daiki Kurihara assisted with the surface roughness and frequency response measurements, respectively.

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