Experimental Evaluation of Sampling Bias in Naturally Seeded Flows.
Final rept. 1 Apr 77-31 Jan 78,
OKLAHOMA STATE UNIV STILLWATER SCHOOL OF MECHANICAL AND AEROSPACE ENGINEERING
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Individual realization laser velocimeter measurements were made in the viscous sublayer of a turbulent channel flow. The Doppler signals were recorded on magnetic tape and then processed with systematic variations in the triggering levels in the counter processors. Naturally seeded flows were modeled by using 0-10 micrometers test dust for scattering centers while flows seeded with 5-10 micrometers test dust were used as a controlled comparison. Both the number density of the scattering particles and the detection level of the counter processors were independently varied to yield a wide range of particle arrival rates. Also, and attempt was made to prove the existance of sampling bias in naturally seeded flows by comparing the slopes of both the unweighted and the weighted corrected for sampling bias velocity profiles with the slope deduced from pressure drop measurements. The results show that sampling bias is not effected by the particle arrival rate. There was, also, no indication that sampling bias is either eliminated for decreased due to differences in the probability for detecting small particles that are moving slowly compared to small particles that are moving fast. The comparisons of velocity gradients with pressure drop measurements were inconclusive. Author
- Fluid Mechanics