Accession Number:

ADA056773

Title:

Experimental Evaluation of Sampling Bias in Naturally Seeded Flows.

Descriptive Note:

Final rept. 1 Apr 77-31 Jan 78,

Corporate Author:

OKLAHOMA STATE UNIV STILLWATER SCHOOL OF MECHANICAL AND AEROSPACE ENGINEERING

Personal Author(s):

• Tiederman,W. G.

Report Date:

1978-06-23

Pagination or Media Count:

34.0

Abstract:

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

Descriptors:

• *TURBULENT FLOW
• *VISCOUS FLOW
• *CHANNEL FLOW
• SHEAR PROPERTIES
• TURBULENT BOUNDARY LAYER
• SAMPLING
• DOPPLER EFFECT
• LASER VELOCIMETERS
• SEEDING

Subject Categories:

• Fluid Mechanics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE