Heat Transfer From Air-Cooled Contrarotating Disks

1997 ◽  
Vol 119 (1) ◽  
pp. 61-67 ◽  
Author(s):  
J.-X. Chen ◽  
X. Gan ◽  
J. M. Owen
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Flow Rate ◽  
Reynolds Numbers ◽  
The Other ◽  
Reynolds Analogy ◽  
Flow Rates ◽  
Nusselt Numbers ◽  
Radial Outflow ◽  
Equivalent Conditions

A superposed radial outflow of air is used to cool two disks that are rotating at equal and opposite speeds at rotational Reynolds numbers up to 1.2 × 106. One disk, which is heated up to 100°C, is instrumented with thermocouples and fluxmeters; the other disk, which is unheated, is made from transparent polycarbonate to allow the measurement of velocity using an LDA system. Measured Nusselt numbers and velocities are compared with computations made using an axisymmetric elliptic solver with a low-Reynolds-number k–ε turbulence model. Over the range of flow rates and rotational speeds tested, agreement between the computations and measurements is mainly good. As suggested by the Reynolds analogy, the Nusselt numbers for contrarotating disks increase strongly with rotational speed and weakly with flow rate; they are lower than the values obtained under equivalent conditions in a rotor–stator system.

Heat Transfer From Air-Cooled Contra-Rotating Discs

1995 ◽  
Author(s):  
Jian-Xin Chen ◽  
Xiaopeng Gan ◽  
J. Michael Owen
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Reynolds Numbers ◽  
The Other ◽  
Reynolds Analogy ◽  
Flow Rates ◽  
Nusselt Numbers ◽  
Rotating Discs ◽  
Radial Outflow ◽  
Equivalent Conditions

A superposed radial outflow of air is used to cool two discs that are rotating at equal and opposite speeds at rotational Reynolds numbers up to 1.2 × 106. One disc, which is heated up to 100°C, is instrumented with thermocouples and fluxmeters; the other disc, which is unheated, is made from transparent polycarbonate to allow the measurement of velocity using an LDA system. Measured Nusselt numbers and velocities are compared with computations made using an axisymmetric elliptic solver with a low-Reynolds-number k-ε turbulence model. Over the range of flow rates and rotational speeds tested, agreement between the computations and measurements is mainly good. As suggested by the Reynolds analogy, the Nusselt numbers for contra-rotating discs increase strongly with rotational speed and weakly with flow rate; they are lower than the values obtained under equivalent conditions in a rotor-stator system.

scholarly journals Heat Transfer in an Air-Cooled Rotor-Stator System

1994 ◽  
Author(s):  
Jian-Xin Chen ◽  
Xiaopeng Gan ◽  
J. Michael Owen
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Turbulence Model ◽  
Computational Study ◽  
Reynolds Numbers ◽  
Flow Rates ◽  
Nusselt Numbers ◽  
Heated Disc ◽  
Radial Outflow ◽  
Cooling Air

This paper describes a combined experimental and computational study of the heat transfer from an electrically-heated disc rotating close to an unheated stator. A radial outflow of cooling air was used to remove heat from the disc, and local Nusselt numbers were measured, using fluxmeters at seven radial locations, for nondimensional flow rates up to C = 9680 and rotational Reynolds numbers up to Reφ = 1.2 × 106. Computations were carried out using an elliptic solver with a low-Reynolds-number k-ε turbulence model, and the agreement between the measured and computed velocities and Nusselt numbers was mainly good.

Heat Transfer in an Air-Cooled Rotor–Stator System

1996 ◽  
Vol 118 (3) ◽  
pp. 444-451 ◽  
Author(s):  
J.-X. Chen ◽  
X. Gan ◽  
J. M. Owen
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Turbulence Model ◽  
Computational Study ◽  
Reynolds Numbers ◽  
Flow Rates ◽  
Nusselt Numbers ◽  
Heated Disk ◽  
Radial Outflow ◽  
Cooling Air

This paper describes a combined experimental and computational study of the heat transfer from an electrically heated disk rotating close to an unheated stator. A radial outflow of cooling air was used to remove heat from the disk, and local Nusselt numbers were measured, using fluxmeters at seven radial locations, for nondimensional flow rates up to Cw = 9680 and rotational Reynolds numbers up to Reφ = 1.2 × 106 Computations were carried out using an elliptic solver with a low-Reynolds-number k–ε turbulence model, and the agreement between the measured and computed velocities and Nusselt numbers was mainly good.

Local Swirl Chamber Heat Transfer and Flow Structure at Different Reynolds Numbers

1999 ◽  
Vol 122 (2) ◽  
pp. 375-385 ◽  
Author(s):  
C. R. Hedlund ◽  
P. M. Ligrani
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Flow Structure ◽  
Flow Behavior ◽  
Turbine Blades ◽  
Reynolds Numbers ◽  
Local Flow ◽  
Flux Boundary Condition ◽  
Nusselt Numbers ◽  
Swirl Chamber

Local flow behavior and heat transfer results are presented from two swirl chambers, which model passages used to cool the leading edges of turbine blades in gas turbine engines. Flow results are obtained in an isothermal swirl chamber. Surface Nusselt number distributions are measured in a second swirl chamber (with a constant wall heat flux boundary condition) using infrared thermography in conjunction with thermocouples, energy balances, and in situ calibration procedures. In both cases, Reynolds numbers Re based on inlet duct characteristics range from 6000 to about 20,000. Bulk helical flow is produced in each chamber by two inlets, which are tangent to the swirl chamber circumference. Important changes to local and globally averaged surface Nusselt numbers, instantaneous flow structure from flow visualizations, and distributions of static pressure, total pressure, and circumferential velocity are observed throughout the swirl chambers as the Reynolds number increases. Of particular importance are increases of local surface Nusselt numbers (as well as ones globally averaged over the entire swirl chamber surface) with increasing Reynolds number. These are tied to increased advection, as well as important changes to vortex characteristics near the concave surfaces of the swirl chambers. Higher Re also give larger axial components of velocity, and increased turning of the flow from each inlet, which gives Go¨rtler vortex pair trajectories greater skewness as they are advected downstream of each inlet. [S0889-504X(00)00502-X]

Numerical Simulations of Resonant Heat Transfer Augmentation at Low Reynolds Numbers

2001 ◽  
Author(s):  
Miles Greiner ◽  
Paul F. Fischer ◽  
Henry Tufo
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Natural Frequency ◽  
Flow Rate ◽  
Low Reynolds Number ◽  
Reynolds Numbers ◽  
Spectral Element ◽  
Pumping Power ◽  
Number Systems ◽  
Low Reynolds

Abstract The effect of flow rate modulation on low Reynolds number heat transfer enhancement in a transversely grooved passage was numerically simulated using a two-dimensional spectral element technique. Simulations were performed at subcritical Reynolds numbers of Rem = 133 and 267, with 20% and 40% flow rate oscillations. The net pumping power required to modulate the flow was minimized as the forcing frequency approached the predicted natural frequency. However, mixing and heat transfer levels both increased as the natural frequency was approached. Oscillatory forcing in a grooved passage requires two orders of magnitude less pumping power than flat passage systems for the same heat transfer level. Hydrodynamic resonance appears to be an effective method of increasing heat transfer in low Reynolds number systems where pumping power is at a premium, such as micro heat transfer applications.

scholarly journals Local Swirl Chamber Heat Transfer and Flow Structure at Different Reynolds Numbers

1999 ◽  
Author(s):  
C. R. Hedlund ◽  
P. M. Ligrani
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Flow Structure ◽  
Flow Behavior ◽  
Turbine Blades ◽  
Reynolds Numbers ◽  
Local Flow ◽  
Flux Boundary Condition ◽  
Nusselt Numbers ◽  
Swirl Chamber

Local flow behavior and heat transfer results are presented from two swirl chambers, which model passages used to cool the leading edges of turbine blades in gas turbine engines. Flow results are obtained in an isothermal swirl chamber. Surface Nusselt number distributions are measured in a second swirl chamber (with a constant wall beat flux boundary condition) using infrared thermography, in conjunction with thermocouples, energy balances, and in situ calibration procedures. In both cases, Reynolds numbers Re based on inlet duct characteristics range from 6000 to about 20000. Bulk helical flow is produced in each chamber by two inlets which ore tangent to the swirl chamber circumference. Important changes to local and globally-averaged surface Nusselt numbers, instantaneous flow structure from flow visualizations, and distributions of static pressure, total pressure, and circumferential velocity are observed throughout the swirl chambers as the Reynolds number increases. Of particular importance are increases of local surface Nusselt numbers (as well as ones globally-averaged over the entire swirl chamber surface) with increasing Reynolds number. These are tiad to increased advection, as well as important changes to vortex characteristics near the concave surfaces of the swirl chambers. Higher Re also give larger axial components of velocity, and increased turning of the flow from each inlet, which gives Görtler vnrtex pair trajectories greater skewness as they are advected downstream of each inlet.

Effects of a Realistically Rough Surface on Vane Heat Transfer Including the Influence of Turbulence Condition and Reynolds Number

2011 ◽  
Vol 134 (2) ◽  
Author(s):  
E. L. Erickson ◽  
F. E. Ames ◽  
J. P. Bons
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Rough Surface ◽  
Reynolds Numbers ◽  
Suction Surface ◽  
Average Roughness ◽  
Surface Distribution ◽  
Reynolds Analogy ◽  
Pressure Surface ◽  
Early Transition

Heat transfer distributions are experimentally acquired and reported for a vane with both a smooth and a realistically rough surface. Surface heat transfer is investigated over a range of turbulence levels (low (0.7%), grid (8.5%), aerocombustor (13.5%), and aerocombustor with decay (9.5%)) and a range of chord Reynolds numbers (ReC=500,000, 1,000,000, and 2,000,000). The realistically rough surface distribution was generated by Brigham Young University’s accelerated deposition facility. The surface is intended to represent a TBC surface that has accumulated 7500 h of operation with particulate deposition due to a mainstream concentration of 0.02 ppmw. The realistically rough surface was scaled by 11 times for consistency with the vane geometry and cast using a high thermal conductivity epoxy (k=2.1 W/m/K) to comply with the vane geometry. The surface was applied over the foil heater covering the vane pressure surface and about 10% of the suction surface. The 958×573 roughness array generated by Brigham Young on a 9.5×5.7 mm2 region was averaged to a 320×191 array for fabrication. The calculated surface roughness parameters of this scaled and averaged array included the maximum roughness, Rt=1.99 mm, the average roughness, Ra=0.25 mm, and the average forward facing angle, αf=3.974 deg. The peak to valley roughness, Rz, was determined to be 0.784 mm. The sand grain roughness of the surface (kS=0.466 mm) was estimated using a correlation offered by Bons (2005, “A Critical Assessment of Reynolds Analogy for Turbine Flows,” ASME J. Turbomach., 127, pp. 472–485). Based on estimates of skin friction coefficient using a turbulence correlation with the vane chord Reynolds numbers representative values for the surface’s roughness Reynolds number are 23, 43, and 80 for the three exit condition Reynolds numbers tested. Smooth vane heat transfer distributions exhibited significant laminar region augmentation with the elevated turbulence levels. Turbulence also caused early transition on the pressure surface for the higher Reynolds numbers. The rough surface had no significant effect on heat transfer in the laminar regions but caused early transition on the pressure surface in every case.

Internal and External Cooling of a Full Coverage Effusion Cooling Plate: Effects of Double Wall Cooling Configuration and Conditions

2017 ◽  
Author(s):  
Zhong Ren ◽  
Sneha Reddy Vanga ◽  
Nathan Rogers ◽  
Phil Ligrani ◽  
Keith Hollingsworth ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Film Cooling ◽  
Reynolds Numbers ◽  
Test Plate ◽  
Blowing Ratio ◽  
Spatially Resolved ◽  
Nusselt Numbers ◽  
Streamwise Location ◽  
Effusion Hole

The present study provides new heat transfer data for both the surfaces of the full coverage effusion cooling plate within a double wall cooling test facility. To produce the cooling stream, a cold-side cross-flow supply for the effusion hole array is employed. Also utilized is a unique mainstream mesh heater, which provides transient thermal boundary conditions, after mainstream flow conditions are established. For the effusion cooled surface, presented are spatially-resolved distributions of surface adiabatic film cooling effectiveness, and surface heat transfer coefficients (measured using infrared thermography). For the coolant side, presented are spatially-resolved distributions of surface Nusselt numbers (measured using liquid crystal thermography). Of interest are the effects of streamwise development, blowing ratio, and Reynolds number. Streamwise hole spacing and spanwise hole spacing (normalized by effusion hole diameter) on the effusion plate are 15 and 4, respectively. Effusion hole diameter is 6.35 mm, effusion hole angle is 25 degrees, and effusion plate thickness is 3 hole diameters. Considered are overall effusion blowing ratios from 2.9 to 7.5, with subsonic, incompressible flow, and constant freestream velocity with streamwise development, for two different mainstream Reynolds numbers. For the hot side (mainstream) of the effusion film cooling test plate, results for two mainflow Reynolds numbers of about 145000 and 96000 show that the adiabatic cooling effectiveness is generally higher for the lower Reynolds number for a particular streamwise location and blowing ratio. The heat transfer coefficient is generally higher for the low Reynolds number flow. This is due to altered supply passage flow behavior, which causes a reduction in coolant lift-off of the film from the surface as coolant momentum, relative to mainstream momentum, decreases. For the coolant side of the effusion test plate, Nusselt numbers generally increase with blowing ratio, when compared at a particular streamwise location and mainflow Reynolds number.

Computation of Heat Transfer in Rotating Cavities Using a Two-Equation Model of Turbulence

1990 ◽  
Author(s):  
A. P. Morse ◽  
C. L. Ong
Keyword(s):  
Heat Transfer ◽  
Turbulence Model ◽  
Radial Direction ◽  
Reynolds Numbers ◽  
Systematic Errors ◽  
Equation Model ◽  
Sufficient Accuracy ◽  
Nusselt Numbers ◽  
Radial Outflow ◽  
Cooling Air

The paper presents finite-difference predictions for the convective heat transfer in symmetrically-heated rotating cavities subjected to a radial outflow of cooling air. An elliptic calculation procedure has been used, with the turbulent fluxes estimated by means of a low Reynolds number k-ε model and the familiar ‘turbulence Prandtl number’ concept. The predictions extend to rotational Reynolds numbers of 3.7 × 106 and encompass cases where the disc temperatures may be increasing, constant or decreasing in the radial direction. It is found that the turbulence model leads to predictions of the local and average Nusselt numbers for both discs which are generally within ± 10% of the values from published experimental data, although there appear to be larger systematic errors for the upstream disc than for the downstream disc. It is concluded that the calculations are of sufficient accuracy for engineering design purposes, but that improvements could be brought about by further optimization of the turbulence model.

LES Investigation of Flow and Heat Transfer in a Channel With Dimples and Protrusions

2007 ◽  
Author(s):  
Mohammad A. Elyyan ◽  
Danesh K. Tafti
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Reynolds Numbers ◽  
The Other ◽  
Secondary Effect ◽  
Flow Acceleration ◽  
Heat Transfer Augmentation ◽  
Flow And Heat Transfer ◽  
Separated Shear Layer ◽  
Dimple Surface

LES calculations are conducted for flow in a channel with dimples and protrusions on opposite walls with both surfaces heated at three Reynolds numbers, ReH = 220, 940, and 9300 ranging from laminar, weakly turbulent to fully turbulent, respectively. Turbulence generated by the separated shear layer in the dimple and along the downstream rim of the dimple is primarily responsible for heat transfer augmentation on the dimple surface. On the other hand, augmentation on the protrusion surface is mostly driven by flow impingement and flow acceleration between protrusions, while the turbulence generated in the wake has a secondary effect. Heat transfer augmentation ratios of 0.99 at ReH = 220, 2.9 at ReH = 940, and 2.5 at ReH = 9300 are obtained. Both skin friction and form losses contribute to pressure drop in the channel, with form losses increasing from 45% to 80% with an increase in the Reynolds number. Friction coefficient augmentation ratios of 1.67, 4.82 and 6.37 are obtained at ReH = 220, 940, and 9300, respectively. Based on the geometry studied, it is found that dimples and protrusions may not be viable heat transfer augmentation surfaces when the flow is steady and laminar.

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