Heat Transfer Measurements in a Compressible Flow Vane Cascade Showing the Influence of Reynolds Number, Mach Number, and Turbulence Level on Transition and Augmentation of Laminar Heat Transfer by Free-Stream Turbulence

2014 ◽  
Author(s):  
Kristin Stahl ◽  
Leolein P. Moualeu ◽  
Jonathan E. Long ◽  
Forrest E. Ames ◽  
Yildirim B. Suzen
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Mach Number ◽  
Compressible Flow ◽  
Free Stream ◽  
Turbulence Level ◽  
Free Stream Turbulence

Free-Stream Turbulence Effects on Local Heat Transfer from a Sphere

1972 ◽  
Vol 94 (1) ◽  
pp. 7-14 ◽  
Author(s):  
L. B. Newman ◽  
E. M. Sparrow ◽  
E. R. G. Eckert
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Reynolds Number ◽  
Free Stream ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Heat Flux Sensor ◽  
Forward Region ◽  
Number Range ◽  
Free Stream Turbulence

Experiments involving both heat-transfer and turbulence-field measurements were performed to determine the influence of free-stream turbulence on the local heat transfer from a sphere situated in a forced-convection airflow. The research was facilitated by a miniature heat-flux sensor which could be positioned at any circumferential location on the equator of the sphere. Turbulence grids were employed to generate free-stream turbulence with intensities of up to 9.4 percent. The Reynolds-number range of the experiments was from 20,000 to 62,000. The results indicate that the local heat flux in the forward region of the sphere is uninfluenced by free-stream turbulence levels of up to about 5 percent. For higher turbulence levels, the heat-flux increases with the turbulence intensity, the greatest heat-flux augmentation found here being about 15 percent. Furthermore, at the higher turbulence intensities, there appears to be a departure from the half-power Reynolds-number dependence of the stagnation-point Nusselt number. Turbulent separation occurred at Reynolds numbers of 42,000 and 62,000 for a turbulence level of 9.4 percent, these values being well below the transition Reynolds number of 2 × 105 for a sphere situated in a low-turbulence flow.

scholarly journals Reynolds, Mach and free-stream turbulence effects on the flow in a low-pressure turbine

2021 ◽  
pp. 1-17
Author(s):  
Maxime Fiore ◽  
Nicolas Gourdain
Keyword(s):  
Reynolds Number ◽  
Mach Number ◽  
Free Stream ◽  
Guide Vane ◽  
Flow Behavior ◽  
Suction Side ◽  
Boundary Layer Separation ◽  
Low Pressure ◽  
Free Stream Turbulence ◽  
Low Pressure Turbine

Abstract This paper presents the Large Eddy Simulation of a Low-Pressure Turbine Nozzle Guide Vane for different Reynolds (Re) and Mach numbers (Ma) with or without inlet turbulence prescribed. The analysis is based on a slice of a LPT blading representative of a midspan flow. The characteristic Re of the LPT can vary by a factor of four between take-off and cruise conditions. In addition, the LPT operates at different Ma and the incident flow can have significant levels of turbulence due to upstream blade wakes. The paper investigates numerically using LES the flow around a LPT blading with three different Reynolds number Re = 175'000 (cruise), 280'000 (mid-level altitude) and 500'000 (take-off) keeping the same characteristic Mach number Ma = 0.2 and three different Mach number Ma = 0.2, 0.5 and 0.8 keeping the same Reynolds number Re= 280'000. These different simulations are performed with 0% Free Stream Turbulence (FST) followed by inlet turbulence (6% FST). The study focuses on different flow characteristics: pressure distribution around the blade, near-wall flow behavior, loss generation and Turbulent Kinetic Energy budget. The results show an earlier boundary layer separation on the aft of the blade suction side when the Re is increased while the free-stream turbulence delays separation. The TKE budget shows the predominant effect of the turbulent production and diffusion in the wake, the axial evolution of these different terms being relatively insensitive to Re and Ma.

Pressure Distribution and Heat Transfer for Flow Over Simulated Cylindrical Parachutes

1965 ◽  
Vol 87 (4) ◽  
pp. 521-525 ◽  
Author(s):  
J. C. Y. Koh ◽  
J. P. Hartnett
Keyword(s):  
Heat Transfer ◽  
Pressure Distribution ◽  
Free Stream ◽  
Turbulence Level ◽  
Heat Transfer Characteristics ◽  
Free Stream Turbulence ◽  
Transfer Characteristics ◽  
Cylindrical Cup

The aerodynamic and heat-transfer characteristics for flow over an upstream-facing cylindrical cup simulating a parachute geometry were studied. It was found that: (1) The pressure on the bottom of the cup increases as the depth of the cup increases. (2) An increase in the free-stream turbulence level increases the aerodynamic heat transfer significantly. (3) The heat transfer front the bottom of the cup decreases monotonically as the depth of the cup increases. (4) The effect of suction at the cup bottom is to equalize the pressure distribution and to increase the heat transfer.

Compressor blade leading edges in subsonic compressible flow

2000 ◽  
Vol 214 (1) ◽  
pp. 221-242 ◽  
Author(s):  
L Tain ◽  
N. A. Cumpsty
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Mach Number ◽  
Free Stream ◽  
Separation Bubble ◽  
Leading Edge ◽  
Inviscid Flow ◽  
Compressor Blade ◽  
Free Stream Turbulence ◽  
Mach Numbers

The flow around the leading edge of a compressor blade is interesting and important because there is such a strong interaction between the viscous boundary layer flow and the inviscid flow around it. As the velocity of the inviscid flow just outside the boundary layer is increased from subsonic to supersonic, the type of viscous-inviscid interaction changes; this has important effects on the boundary layer downstream and thus on the performance of the aerofoil or blade. An investigation has been undertaken of the flow in the immediate vicinity of a simulated compressor blade leading edge for a range of inlet Mach numbers from 0.6 to 0.95. The two-dimensional aerofoil used has a circular leading edge on the front of a flat aerofoil. The incidence, Reynolds number and level of free-stream turbulence have been varied. Measurements include the static pressure around the leading edge and downstream and the boundary layer profile far enough downstream for the leading edge bubble to have reattached. Schlieren pictures were also obtained. The flow around the leading edge becomes supersonic when the inlet Mach number is 0.7 for the zero-incidence case; for an inlet Mach number of 0.95 the peak Mach number was approximately 1.7. The pattern of flow around the leading edge alters as the Mach number is increased, and at the highest Mach number tested here the laminar separation bubble is removed. Positive incidence, raised free-stream turbulence or increased Reynolds number at intermediate inlet Mach numbers tended to promote flow patterns similar to those seen at the highest inlet Mach number. Both increased free-stream turbulence and increased Reynolds number, for the same Mach number and incidence, produced thinner shear layers including a thinner boundary layer well downstream. The measurements were supported by calculations using the MSES code (the single aerofoil version of the MISES code); the calculations were helpful in interpreting the measured results and were demonstrated to be accurate enough to be used for design purposes.

Assessment of Transition Modeling for the Design of Controlled Diffusion Airfoil Compressor Cascades

2013 ◽  
Author(s):  
Vincent Marciniak ◽  
Marco Longhitano ◽  
Edmund Kügeler
Keyword(s):  
Reynolds Number ◽  
Mach Number ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Bypass Transition ◽  
Compressor Cascade ◽  
Free Stream Turbulence ◽  
Wide Range ◽  
Transition Models ◽  
Transition Modeling

The aim of this paper is to investigate whether correlation-based transition models can be used for the design of CDA profiles. To this end, a CDA compressor cascade has been widely experimentally investigated at DLR Cologne. Off-design measurements have been carried out and the influence of the variation of four flow parameters has been investigated: The inlet Mach number, the incidence, the chord-based Reynolds number and the free-stream turbulence intensity. The inlet Mach number has been varied from 0.5 up to 0.8. The incidence was varied over the whole working range and beyond. Realistic values of the Reynolds number and of the free-stream turbulence intensity have been attained. Hence, the test case apt to assess the capacity of the DLR’s in-house turbomachinery specific CFD code TRACE to design modern compressor blades. In this paper, computations simulating the influence of those four parameters on the performance of the CDA profile are presented and compared to the measurements. Two transition models are used for this study: an in-house model denoted MultiMode model and the γ-ReΘ model. In addition, two turbulence models (Wilcox k-ω and Menter k-ω SST) and their turbomachinery extensions have also been used for this study. The results between the different numerical simulations and the measurements are discussed in term of loss coefficients and Mach number distributions. The computed losses are close to the experimental values and the physics of the flow is also well reproduced. Bypass transition as well as laminar separation bubbles have been simulated in accordance with the experimental observations. Hence, the TRACE code is able to predict the onset of transition over a wide range of flow conditions.

scholarly journals Mass Transfer Cooling on a Porous Flat Plate in Carbon-Dioxide and Air Streams

1968 ◽  
Vol 90 (4) ◽  
pp. 596-600 ◽  
Author(s):  
A. L. Laganelli ◽  
J. P. Hartnett
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Mach Number ◽  
Flat Plate ◽  
Transpiration Rate ◽  
Free Stream ◽  
Recovery Factor ◽  
Effective Length ◽  
Number Range ◽  
Porous Flat Plate

Heat transfer results are reported for a transpiration cooled porous flat plate placed in a stream of air and in a stream of CO2. The tests were performed at a Mach number of 1.96 over a range of effective length Reynolds number, from 5 million to 9.1 million, when CO2 was used as the free stream gas. A Mach number of 2.53 for an effective length Reynolds number range of 5.3 million to 8.3 million was characteristic when the free stream gas was air. The heat transfer data were normalized and presented as the ratio of the Stanton number to the no-blowing Stanton value (St/St0) as a function of the dimensionless transpiration rate F/St0. The recovery factor data were also normalized and presented as the ratio of r/r0 as a function of the transpiration rate F. The results for both the air and the CO2 free stream flows showed a reduction in heat transfer with increasing transpiration rate, using air and CO2 as the injectant gases. The measured recovery factor and the normalized recovery factor also decreased with increasing transpiration for the reported gas combinations. It was found that Rubesin’s air theory adequately predicts all of the heat transfer results including those obtained in CO2 atmospheres within the reported Mach number range. Also, the empirical theories which predict recovery factor results for air free streams can be used for air or CO2 injection into a CO2 free stream gas.

Effect of Free-Stream Turbulence on Heat Transfer through a Turbulent Boundary Layer

1978 ◽  
Vol 100 (4) ◽  
pp. 671-677 ◽  
Author(s):  
J. C. Simonich ◽  
P. Bradshaw
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Free Stream ◽  
Reynolds Numbers ◽  
Skin Friction Coefficient ◽  
Reynolds Analogy ◽  
Low Reynolds Numbers ◽  
Free Stream Turbulence ◽  
High Reynolds

Measurements in a boundary layer in zero pressure gradient show that the effect of grid-generated free-stream turbulence is to increase heat transfer by about five percent for each one percent rms increase of the longitudinal intensity. In fact, even a Reynolds analogy factor, 2 × (Stanton number)/(skin-friction coefficient), increases significantly. It is suggested that the irreconcilable differences between previous measurements are attributable mainly to the low Reynolds numbers of most of those measurements. The present measurements attained a momentum-thickness Reynolds number of 6500 (chord Reynolds number approximately 6.3 × 106) and are thought to be typical of high-Reynolds-number flows.

Calculation of Transitional Boundary Layers With an Improved Low-Reynolds-Number Version of the k–ε Turbulence Model

1994 ◽  
Vol 116 (4) ◽  
pp. 765-773 ◽  
Author(s):  
D. Biswas ◽  
Y. Fukuyama
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Boundary Layers ◽  
Turbulent Flows ◽  
Free Stream ◽  
Low Reynolds Number ◽  
Turbine Rotor ◽  
Limiting Behavior ◽  
Free Stream Turbulence ◽  
Low Reynolds

Several well-known low-Reynolds-number versions of the k–ε models are analyzed critically for laminar to turbulent transitional flows as well as near-wall turbulent flows from a theoretical and numerical standpoint. After examining apparent problems associated with the modeling of low-Reynolds-number wall damping functions used in these models, an improved version of the k–ε model is proposed by defining the wall damping factors as a function of some quantity (turbulence Reynolds number Ret) that is only a rather general indicator of the degree of turbulent activity at any location in the flow rather than a specific function of the location itself, and by considering the wall limiting behavior, the free-stream asymptotic behavior, and the balance between production and destruction of turbulence. This new model is applied to the prediction of (1) transitional boundary layers influenced by the free-stream turbulence, pressure gradient, and heat transfer; (2) external heat transfer distribution on the gas turbine rotor and stator blade under different inlet Reynolds number and free-stream turbulence conditions. It is demonstrated that the present model yields improved predictions.

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