Laminar, Transition, and Turbulent Boundary-Layer Heat-Transfer Measurements With Wall Cooling in Turbulent Airflow Through a Tube

1969 ◽  
Vol 91 (4) ◽  
pp. 477-487 ◽  
Author(s):  
L. H. Back ◽  
R. F. Cuffel ◽  
P. F. Massier
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Flat Plate ◽  
Reynolds Numbers ◽  
Boundary Layer Transition ◽  
Gas Temperature ◽  
Layer Transition ◽  
Constant Property ◽  
Turbulent Airflow

Heat-transfer measurements were made along the wall in the thermal entrance region of a high-temperature turbulent airflow through a cooled tube 8.6 dia long. There was simultaneous development of the velocity and temperature profiles along the tube, the boundary-layer thickness at the inlet being small, compared to the tube radius. The measurements, made over a range of Reynolds numbers based on the tube diameter ReD from 7 × 104 to 106 and wall-to-gas temperature ratio Tw/Tt from 1/3 to 2/3, included natural boundary-layer transition data in the laminar, transition, and turbulent boundary-layer regions, and forced transition data obtained with a trip at the tube inlet. Although the inability to predict boundary-layer transition precludes a general correlation of the data, a fair correlation of the transitional data was obtained by accounting for the effective origin of the boundary layer. Transition Reynolds numbers, on the order of those found for flow over a flat plate, increased with ReD and decreased with wall cooling; i e., decreasing Tw/Tv In the turbulent boundary-layer region, both the natural transition data and tripped data were in general correspondence with the trend of a constant-property flat-plate prediction. However, the turbulent boundary-layer heat-transfer group with properties evaluated at the core flow temperature increased with wall cooling. Other investigations in the turbulent flow region are discussed in light of these measurements.

Effect of Tripping Laminar-to-Turbulent Boundary Layer Transition on Tip Vortex Cavitation

1997 ◽  
Vol 41 (01) ◽  
pp. 1-9
Author(s):  
T. Pichon ◽  
A. Pauchet ◽  
A. Astolfi ◽  
D. H. Fruman ◽  
J-Y. Billard
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Flat Plate ◽  
Cross Section ◽  
Lift Coefficient ◽  
Reynolds Numbers ◽  
Boundary Layer Transition ◽  
Tip Vortex ◽  
Layer Transition ◽  
Tip Vortex Cavitation

It is by now well established that, for Reynolds numbers larger than those corresponding to the conditions of laminar-to-turbulent boundary layer transition over a flat plate (≈0.5 × 106) and for a variety of wing shapes and cross sections, desinent cavitation numbers divided by the Reynolds number to the power 0.4 correlate with the square of the lift coefficient. In the case of foils having an NACA 16020 cross section and for Reynolds numbers below or close to those leading to transition over a flat plate, the results are very much different from those obtained for well-developed turbulent boundary layer conditions. Thus, a research program has been conducted in order to investigate the effect of boundary layer manipulation on cavitation occurrence. It consisted in determining the critical cavitation numbers, the lift coefficients, and the velocities in the tip vortex of foils having either a smooth surface or tripping roughness (promoters) near the leading edge. Tests were performed using elliptical foils of NACA 16020 cross section having the promoters extending over 60, 80 and 90 percent of the semi-span. The region near the tip was kept smooth in order to distinguish laminar-to-turbulent transition effects from tip vortex cavitation inhibition effects associated with artificial roughness at the wing tip. Results obtained at very low Reynolds numbers, ≥ 0.24 × 106, with the foil tripped on both the pressure and suction sides collapse rather well with those previously obtained at much larger Reynolds numbers with the smooth foil, and correlate with the square of the lift coefficient. The differences between the tripped and smooth foil results are due to the modification of the lift characteristics through the modification of the wing boundary layer, as shown by flow visualization studies, and as a result of the local tip vortex intensity.

An Experimental Study of Heat Transfer on an Outlet Guide Vane

2014 ◽  
Author(s):  
Chenglong Wang ◽  
Lei Wang ◽  
Bengt Sundén ◽  
Valery Chernoray ◽  
Hans Abrahamsson
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Turbulent Boundary Layer ◽  
Guide Vane ◽  
Incidence Angle ◽  
Boundary Layer Transition ◽  
Transfer Coefficients ◽  
Suction Surface ◽  
Layer Transition

In the present study, the heat transfer characteristics on the suction and pressure sides of an outlet guide vane (OGV) are investigated by using liquid crystal thermography (LCT) method in a linear cascade. Because the OGV has a complex curved surface, it is necessary to calibrate the LCT by taking into account the effect of viewing angles of the camera. Based on the calibration results, heat transfer measurements of the OGV were conducted. Both on- and off-design conditions were tested, where the incidence angles of the OGV were 25 degrees and −25 degrees, respectively. The Reynolds numbers, based on the axial flow velocity and the chord length, were 300,000 and 450,000. In addition, heat transfer on suction side of the OGV with +40 degrees incidence angle was measured. The results indicate that the Reynolds number and incidence angle have considerable influences upon the heat transfer on both pressure and suction surfaces. For on-design conditions, laminar-turbulent boundary layer transitions are on both sides, but no flow separation occurs; on the contrary, for off-design conditions, the position of laminar-turbulent boundary layer transition is significantly displaced downstream on the suction surface, and a separation occurs from the leading edge on the pressure surface. As expected, larger Reynolds number gives higher heat transfer coefficients on both sides of the OGV.

Coherent structures in bypass transition induced by a cylinder wake

2008 ◽  
Vol 603 ◽  
pp. 367-389 ◽  
Author(s):  
CHONG PAN ◽  
JIN JUN WANG ◽  
PAN FENG ZHANG ◽  
LI HAO FENG
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Flat Plate ◽  
Boundary Layer Transition ◽  
Wake Vortex ◽  
Bypass Transition ◽  
Cylinder Wake ◽  
Layer Transition ◽  
Vortical Structures ◽  
Free Stream Turbulence

Flat-plate boundary layer transition induced by the wake vortex of a two-dimensional circular cylinder is experimentally investigated. Combined visualization and velocity measurements show a different transition route from the Klebanoff mode in free-stream turbulence-induced transition. This transition scenario is mainly characterized as: (i) generation of secondary transverse vortical structures near the flat plate surface in response to the von Kármán vortex street of the cylinder; (ii) formation of hairpin vortices due to the secondary instability of secondary vortical structures; (iii) growth of hairpins which is accelerated by wake-vortex induction; (iv) formation of hairpin packets and the associated streaky structures. Detailed investigation shows that during transition the evolution dynamics and self-sustaining mechanisms of hairpins, hairpin packets and streaks are consistent with those in a turbulent boundary layer. The wake vortex mainly plays the role of generating and destabilizing secondary transverse vortices. After that, the internal mechanisms become dominant and lead to the setting up of a self-sustained turbulent boundary layer.

Modeling of Rough-Wall Boundary Layer Transition and Heat Transfer on Turbine Airfoils

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
M. Stripf ◽  
A. Schulz ◽  
H.-J. Bauer
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Boundary Layer Transition ◽  
Rough Wall ◽  
Layer Transition ◽  
New Model ◽  
Wall Boundary Layer ◽  
Wall Boundary ◽  
Turbine Airfoils

A new model for predicting heat transfer in the transitional boundary layer of rough turbine airfoils is presented. The new model makes use of extensive experimental work recently published by the current authors. For the computation of the turbulent boundary layer, a discrete element roughness model is combined with a two-layer model of turbulence. The transition region is modeled using an intermittency equation that blends between the laminar and turbulent boundary layer. Several intermittency functions are evaluated in respect of their applicability to rough-wall transition. To predict the onset of transition, a new correlation is presented, accounting for the influence of freestream turbulence and surface roughness. Finally, the new model is tested against transitional rough-wall boundary layer flows on high-pressure and low-pressure turbine airfoils.

Transition of compressible high enthalpy boundary layer flow over a flat plate

1994 ◽  
Vol 98 (972) ◽  
pp. 25-34 ◽  
Author(s):  
Y. He ◽  
R. G. Morgan
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Flat Plate ◽  
Empirical Relation ◽  
Boundary Layer Transition ◽  
Transition To Turbulence ◽  
Layer Transition ◽  
High Enthalpy ◽  
Layer Flow

AbstractThis paper presents the results of an experimental investigation into the characteristics of boundary layer transition to turbulence in hypervelocity air flows. A series of experiments was conducted using a flat plate model, equipped with static pressure and thin film heat transfer transducers, in a free piston shock tunnel. Transition was observed in the stagnation enthalpy range of 2·35 to 19·2 MJ/kg. The transition Reynolds number correlates well with the unit Reynolds number through a simple empirical relation. The influences of Mach number, pressure and wall cooling are examined. The measured heat transfer rates in laminar and turbulent regions are compared with empirical predictions. Freestream disturbances of the test flow were also measured and analysed.

Effects of Reynolds Number and Free-Stream Turbulence on Boundary Layer Transition in a Compressor Cascade

2000 ◽  
Author(s):  
Heinz-Adolf Schreiber ◽  
Wolfgang Steinert ◽  
Bernhard Küsters
Keyword(s):  
Boundary Layer ◽  
Free Stream ◽  
Reynolds Numbers ◽  
Boundary Layer Transition ◽  
Bypass Transition ◽  
Layer Transition ◽  
Free Stream Turbulence ◽  
High Reynolds Numbers ◽  
High Turbulence ◽  
High Reynolds

An experimental and analytical study has been performed on the effect of Reynolds number and free-stream turbulence on boundary layer transition location on the suction surface of a controlled diffusion airfoil (CDA). The experiments were conducted in a rectilinear cascade facility at Reynolds numbers between 0.7 and 3.0×106 and turbulence intensities from about 0.7 to 4%. An oil streak technique and liquid crystal coatings were used to visualize the boundary layer state. For small turbulence levels and all Reynolds numbers tested the accelerated front portion of the blade is laminar and transition occurs within a laminar separation bubble shortly after the maximum velocity near 35–40% of chord. For high turbulence levels (Tu > 3%) and high Reynolds numbers transition propagates upstream into the accelerated front portion of the CDA blade. For those conditions, the sensitivity to surface roughness increases considerably and at Tu = 4% bypass transition is observed near 7–10% of chord. Experimental results are compared to theoretical predictions using the transition model which is implemented in the MISES code of Youngren and Drela. Overall the results indicate that early bypass transition at high turbulence levels must alter the profile velocity distribution for compressor blades that are designed and optimized for high Reynolds numbers.

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