Filtered Rayleigh Scattering Velocimetry - Accuracy Investigation in a M=2.22

Axisymmetric Jet

Jonas Gustavsson

Corin Segal

Mechanical and Aerospace Engineering

University of Florida

January 2004

Purpose of study

• Measure the accuracy of FRS for high-speed flow velocimetry in a realistic flow situation

• Identify and quantify dominating sources of uncertainty

• Propose ways of reducing total uncertainty

Experimental setup

Axisymmetric Ø11 mm M=2.2 Free jet

• Well-known flow with suitable Mach number range

• No optical access issues

• Comparison to pressure probe surveys possible

current setupEggers 1966 Pitot survey

Experimental setup

Experimental setup

Experimental procedure

Sets of images

• Ambient light

• White field

• Dot card

• Iodine cell calibration

• Jet images

Iodine cell calibration

4.4 V

4.3 V

4.2 V

Uneven seeding

Unfiltered image Transmission image

Results

Uncertainty sources

• Laser drift 3h 35 m/s

• Image overlap 0.15 pixels 10 m/s

• Shot noise 10 m/s

• Finite spectral width 10 m/s

Total uncertainty: 40 m/s

Conclusions

• FRS is a viable velocity measurement technique in a practical flow situation

• Water vapor condensation limits light collection shot noise, but droplets track flow well

• Laser drift dominates, but several sources contribute O(10 m/s)

• Total estimated error ±40 m/s agrees well with experimental data

Future work

• Improve the accuracy through better laser wavelength control.

• Develop methods for analyzing data from FRS in unevenly, moderately seeded flows.

• Assess FRS for simultaneous measurement of velocity and temperature in high-speed combustion flows.

The End