Prepared for

Lewis Research Center

Under Grant NAG3–230

Ki-Hyeon Sohn and Eli Reshotko

Case Western Reserve University

Cleveland, Ohio

Experimental Study of Boundary Layer

Transition With Elevated Freestream

Turbulence on a Heated Flat Plate

NASA Contractor Report 187068

February 1991

National Aeronautics and

Space Administration








































































































































































































































































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National Aeronautics and Space Administration

John H. Glenn Research Center at Lewis Field

Cleveland, Ohio 44135–3191

February 1991

NASA CR–187068

E–12252

267

A12

Experimental Study of Boundary Layer Transition With Elevated

Freestream Turbulence on a Heated Flat Plate

Ki-Hyeon Sohn and Eli Reshotko

By-pass transition; Heat transfer; Flat plate

WU–505–62–52–00

NAG3–230

Case Western Reserve University

Department of Mechanical and Aerospace Engineering

Cleveland, Ohio 44106

Unclassified -Unlimited

Subject Category: 34

Project Manager, Frederick F. Simon, Internal Fluid Mechanics Division, NASA Lewis Research Center.

A detailed investigation to document momentum and thermal development of boundary layers undergoing natural transition on a

heated flat plate was performed. Experimental results of both overall and conditionally sampled characteristics of laminar, transitional

and low Reynolds number turbulent boundary layers are presented. Measurements were acquired in a low-speed, closed-loop wind

tunnel with a freestream velocity of 100 ft/s and zero pressure gradient over a range of freestream turbulence intensities (TI) from

0.4% to 6%. The distributions of skin friction, heat transfer rate and Reynolds shear stress were all consistent with previously

published data. Reynolds analogy factors for Reθ < 2300 were found to be well predicted by laminar and turbulent correlations which

accounted for an unheated starting length. The measured laminar value of Reynolds analogy factor was as much as 53% higher than

Pr–2/3. A small dependence of turbulent results on TI was observed. Conditional sampling performed in the transitional boundary layer

indicated the existence of a near-wall drop in intermittency, pronounced at certain low intermittencies, which is consistent with the

cross-sectional shape of turbulent spots observed by others. Non-turbulent intervals were observed to possess large magnitudes of

near-wall unsteadiness and turbulent intervals had peak values as much as 50% higher than were measured at fully turbulent stations.

Non-turbulent and turbulent profiles in transitional boundary layers cannot be simply treated as Blasius and fully turbulent profiles,

respectively. The boundary layer spectra indicate predicted selective amplification of T-S waves for TI ≈ 0.4%. However, for TI ≈ 0.8%

and 1.1%, T-S waves are localized very near the wall and do not play a dominant role in the transition process.