Development of flat-plate thermal and velocity boundary layers under highly turbulent and instable air flows: Reynolds numbers ranging from 8400 to 127000

2004 ◽  
Vol 43 (11) ◽  
pp. 1091-1100 ◽  
Author(s):  
Alain Kondjoyan ◽  
Frédéric Péneau ◽  
Henri-Claude Boisson
Keyword(s):  
Flat Plate ◽  
Boundary Layers ◽  
Reynolds Numbers ◽  
Air Flows

A Study on Turbulent Boundary Layers on a Smooth Flat Plate in an Open Channel

2001 ◽  
Vol 123 (2) ◽  
pp. 394-400 ◽  
Author(s):  
Ram Balachandar ◽  
D. Blakely ◽  
M. Tachie ◽  
G. Putz
Keyword(s):  
Flat Plate ◽  
Froude Number ◽  
Boundary Layers ◽  
Open Channel ◽  
Reynolds Numbers ◽  
Turbulent Boundary Layers ◽  
Wall Region ◽  
Mean Velocity ◽  
Number Range ◽  
High Reynolds

An experimental study was undertaken to investigate the characteristics of turbulent boundary layers developing on smooth flat plate in an open channel flow at moderately high Froude numbers (0.25<Fr<1.1) and low momentum thickness Reynolds numbers 800<Reθ<2900. The low range of Reynolds numbers and the high Froude number range make the study important, as most other studies of this type have been conducted at high Reynolds numbers and lower Froude numbers (∼0.1). Velocity measurements were carried out using a laser-Doppler anemometer equipped with a beam expansion device to enable measurements close to the wall region. The shear velocities were computed using the near-wall measurements in the viscous subregion. The variables of interest include the longitudinal mean velocity, the turbulence intensity, and the velocity skewness and flatness distributions across the boundary layer. The applicability of a constant Coles’ wake parameter (Π=0.55) to open channel flows has been discounted. The effect of the Froude number on the above parameters was also examined.

The Influence of Deterministic Surface Roughness and Free-Stream Turbulence on Transitional Boundary Layers: Heat Transfer Distributions and a New Transition Onset Correlation

2021 ◽  
Author(s):  
Christoph Gramespacher ◽  
Matthias Stripf ◽  
Hans-Jörg Bauer
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Flat Plate ◽  
Boundary Layers ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Reynolds Numbers ◽  
Data Set ◽  
Length Scales ◽  
Free Stream Turbulence

Abstract Heat transfer measurements in transitional flat plate boundary layers subjected to surface roughness, strong pressure gradients and free stream turbulence are presented. The surfaces considered, consist of a smooth reference and twenty six deterministic surface topographies that vary in roughness element aspect ratio, height and density. They are designed to cover the full range of roughness regimes from smooth over transitionally rough to fully rough. For each surface, two pressure distributions, characteristic for a suction and a pressure side turbine vane, are investigated. Inlet Reynolds numbers range from 3.0 · 105 to 6.0 · 105 and inlet turbulence intensity is varied between 1% to 8%. Furthermore, different turbulence Reynolds numbers, i.e. turbulence length scales, are realized while the incident turbulence intensity is kept constant. Additionally, the turbulence intensity and Reynolds stress distributions in the free-stream along the flat plate are measured using x-wire probes. Results show a strong influence of roughness and turbulence intensity on the onset of transition. The new data set is used to develop an improved correlation considering the roughness height, density and shape as well as the turbulence intensity and turbulent length scales.

Experimental Investigation by IR-Thermography of Heat Transfer Over Rib-Roughened Surfaces

2010 ◽  
Author(s):  
Damiano Fustinoni ◽  
Alfonso Niro
Keyword(s):  
Heat Transfer ◽  
Flat Plate ◽  
Room Temperature ◽  
Flow Direction ◽  
Reynolds Numbers ◽  
Ir Thermography ◽  
Heat Transfer Characteristics ◽  
Side Ratio ◽  
Air Flows ◽  
Heated Length

This paper presents experimental results on convective heat transfer of air flows over a not-thin plate with different rib-roughness patterns; data over a flat plate are also reported for comparisons. The paper first reviews the technique principles, the experimental setup, and the data processing to recover heat transfer characteristics from IR-thermographic images. Then, thermal performances of three differently ribbed surfaces, namely, with ribs tilted of 90° and 60° angles over flow direction, as well as with 60° V-shape ones are presented and discussed. In all the configurations, the plate is 200 mm long and 150 mm wide, whereas ribs have a square cross-section with 3-mm side, and a corrugation-pitch to rib-side ratio of 13.3. Air flows at room temperature with speed ranging from 2.3 to 11.6 m/s, corresponding to Reynolds numbers at the end of the heated-length between 50000 and 250000, and for a heat flux of near 650 W/m2. For all three enhanced surfaces, the average Nusselt number over the plate horizontal midline shows the same dependence on the Reynolds number as the flat plate, but its values are from 50% to 130% higher with slight differences between the different tested configurations.

Detached shear-layer instability and entrainment in the wake of a flat plate with turbulent separating boundary layers

2015 ◽  
Vol 774 ◽  
pp. 5-36 ◽  
Author(s):  
Man Mohan Rai
Keyword(s):  
Shear Layer ◽  
Flat Plate ◽  
Boundary Layers ◽  
Power Law ◽  
Reynolds Numbers ◽  
Vortex Generation ◽  
Shear Layer Instability ◽  
Trailing Edge ◽  
Velocity Statistics ◽  
Entrainment Process

The near and very near wake of a flat plate with a circular trailing edge, with vigorous vortex shedding, is investigated with data from direct numerical simulations (DNS). Computations were performed for four different combinations of the Reynolds numbers based on plate thickness ($D$) and momentum thickness near the trailing edge (${\it\theta}$). Unlike the case of the cylinder, these Reynolds numbers are independent parameters for the flat plate. The objectives of the study are twofold, to investigate the entrainment process when the separating boundary layers are turbulent and to better understand the instability of the detached shear layers (DSLs). A visualization of the entrainment process, the effect of changing the ratio ${\it\theta}/D$ on entrainment and wake-velocity statistics, and a way of understanding entrainment in a phase-averaged sense via distributions of the turbulent transport rate are provided here. The discussion on shear-layer instability focuses on the role of log-layer eddies in the destabilization process, the effect of high-speed streaks in the turbulent boundary layer in the vicinity of the trailing edge on shear-layer vortex generation rates, and a relationship between the prevalence of shear-layer vortex generation and shedding phase that is a result of an interaction between the shedding process and the shear-layer instability mechanism. A power-law relationship between the ratio of shear-layer and shedding frequencies and the Reynolds numbers mentioned above is obtained. A discussion of the relative magnitudes of the exponents is provided. A second power-law relationship between shed-vortex strength and these two Reynolds numbers is also proposed.

Momentum Thickness Measurements for Thick Axisymmetric Turbulent Boundary Layers

2003 ◽  
Vol 125 (3) ◽  
pp. 569-575 ◽  
Author(s):  
Kimberly M. Cipolla ◽  
William L. Keith
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Flat Plate ◽  
Boundary Layers ◽  
Control Volume ◽  
Scaling Law ◽  
Reynolds Numbers ◽  
Momentum Thickness ◽  
Spatial Growth ◽  
Thickness Measurements

Experimental measurements of the mean wall shear stress and boundary layer momentum thickness on long, thin cylindrical bodies are presented. To date, the spatial growth of the boundary layer and the related boundary layer parameters have not been measured for cases where δ/a (a=cylinder radius) is much greater than one. Moderate Reynolds numbers 104<Reθ<105 encountered in hydrodynamic applications are considered. Tow tests of cylinders with diameters of 0.61, 0.89, and 2.5 mm and lengths ranging from approximately 30 meters to 150 meters were performed. The total drag (axial force) was measured at tow speeds up to 17.4 m/sec. These data were used to determine the tangential drag coefficients on each test specimen, which were found to be two to three times greater than the values for the corresponding hypothetical flat-plate cases. Using the drag measurements, the turbulent boundary layer momentum thickness at the downstream end of the cylindrical bodies is determined, using a control volume analysis. The results show that for the smallest diameter cylinders, there is no indication of relaminarization, and a fully developed turbulent boundary layer exists. A scaling law for the momentum thickness versus length Reynolds number is determined from the data. The results indicate that the spatial growth of the boundary layers over the entire length is less than for a comparable flat-plate case.

Heat Transfer Measurements on a Cooled Flat Plate Simulating Actual Size Turbine Hardware

1999 ◽  
Author(s):  
J. Lepicovsky ◽  
T. J. Bencic
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Mach Number ◽  
Flat Plate ◽  
Boundary Layers ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Transfer Rates ◽  
Cooling Passage

Application of thin-film thermocouples and temperature sensitive paint to surface temperature and heat transfer rate measurement on a flat plate with internal cooling is described in this paper. The test arrangement was designed to model flow and heat transfer conditions in terms of gas (external) and coolant (internal) Reynolds numbers that are typical for cooled turbine components. The test article is geometrically simple; however, from the heat transfer point of view it represents a fairly complex case. For both flows, internal and external, the hydrodynamic boundary layers start well ahead of the thermal boundary layers. The thermally active surface is preceded by an adiabatic starting length. Also, the heat transfer occurs under nonisothermal wall conditions and nonuniform heat flux conditions. The heat transfer experiments were carried out for a range of Mach number and Reynolds number on the gas side from 0.17 to 0.53 and from 135 000 to 580 000, respectively. On the coolant side, the corresponding ranges were from 0.3 to 0.52 for the flow Mach number, and from 20 000 to 65 000 for the Reynolds number. Measured bulk heat transfer rates demonstrated expected trends as functions of external (gas) and internal (coolant) Reynolds numbers. Local heat transfer rates measured along the mid-span line behaved as expected in relation to the internal (coolant) Reynolds number. However, they seem to be insensitive to changes in the external (gas) Reynolds number — at least for the particular test arrangement. Local heat transfer rates, however, strongly depend on the location with respect to the width of the cooling passage. These results were not expected; they may be caused by three dimensional nature of heat convection and conduction in this test arrangement.

scholarly journals Flow phenomena in the very near wake of a flat plate with a circular trailing edge

2014 ◽  
Vol 756 ◽  
pp. 510-543 ◽  
Author(s):  
Man Mohan Rai
Keyword(s):  
Flat Plate ◽  
Boundary Layers ◽  
Reverse Flow ◽  
Reynolds Numbers ◽  
Shear Layers ◽  
Main Body ◽  
Near Wake ◽  
Trailing Edge ◽  
Plate Length ◽  
First Case

AbstractThe very near wake of a flat plate with a circular trailing edge, exhibiting pronounced shedding of wake vortices, is investigated with data from direct numerical simulations (DNSs). Computations were performed for two cases. In the first case the Reynolds numbers based on plate length and thickness were $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}1.255 \times 10^{6}$ and $1.0 \times 10^{4}$, respectively. In the second case the two Reynolds numbers were $3.025 \times 10^{5}$ and $5.0 \times 10^{3}$, respectively. The separating boundary layers are turbulent and statistically identical thus resulting in a wake that is symmetric in the mean. The focus here is on the instability of the detached shear layers and the evolution of rib-vortex-induced localized regions of reverse flow. These regions detach from the main body of reverse flow in the trailing edge region and are convected downstream. The detached shear layers intermittently exhibit unstable behaviour, sometimes resulting in the development of shear-layer vortices as seen in earlier cylinder flow investigations with laminar separating boundary layers. Only a small fraction of the separated turbulent boundary layer experiences this instability, and also rolls up into the initial shed vortices. The instability causes a broadband peak in pressure spectra computed within the shear layers. Phase-averaged intensity and shear stress distributions of the randomly fluctuating component of velocity in the very near wake are also provided here and compared with those obtained in the near wake. The distributions of the production terms in the transport equations for the turbulent stresses are also provided.

The Influence of Deterministic Surface Roughness and Free-Stream Turbulence on Transitional Boundary Layers: Heat Transfer Distributions and a New Transition Onset Correlation

2021 ◽  
pp. 1-13
Author(s):  
Christoph Gramespacher ◽  
Matthias Stripf ◽  
Hans-Jörg Bauer
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Flat Plate ◽  
Boundary Layers ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Reynolds Numbers ◽  
Data Set ◽  
Length Scales ◽  
Free Stream Turbulence

Abstract Heat transfer measurements in transitional flat plate boundary layers subjected to surface roughness, strong pressure gradients and free stream turbulence are presented. The surfaces considered, consist of a smooth reference and twenty six deterministic surface topographies that vary in roughness element aspect ratio, height and density. They are designed to cover the full range of roughness regimes from smooth over transitionally rough to fully rough. For each surface, two pressure distributions, characteristic for a suction and a pressure side turbine vane, are investigated. Inlet Reynolds numbers range from 300000 to 600000 and inlet turbulence intensity is varied between 1 % to 8 %. Furthermore, different turbulence Reynolds numbers, i.e. turbulence length scales, are realized while the incident turbulence intensity is kept constant. Additionally, the turbulence intensity and Reynolds stress distributions in the free-stream along the flat plate are measured using x-wire probes. Results show a strong influence of roughness and turbulence intensity on the onset of transition. The new data set is used to develop an improved correlation considering the roughness height, density and shape as well as the turbulence intensity and turbulent length scales.

Application of V Shape Riblets to Pipe Flows

1991 ◽  
Vol 113 (4) ◽  
pp. 587-590 ◽  
Author(s):  
Shin-ichi Nakao
Keyword(s):  
Reynolds Number ◽  
Drag Reduction ◽  
Flat Plate ◽  
Boundary Layers ◽  
Plate Boundary ◽  
Reynolds Numbers ◽  
Pipe Flows ◽  
Maximum Drag Reduction

Pipes with V shape riblets were tested at Reynolds numbers between 5×103 and 4×104. All riblet pipes indicated some drag reduction. The model with h = 0.55 mm and h/S = 0.483 showed the maximum drag reduction of 8 percent and the widest range of Reynolds number over which the riblet reduces drag. The riblet shape desirable for drag reduction in pipe flows was almost the same as that in flat plate boundary layers, but the value of S+ which provided the maximum drag reduction was quite different; S+ = 23 for pipe flows and S+ = 12 for flat plate boundary layers.

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