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.

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

2010 ◽  
Author(s):  
E. L. Erickson ◽  
F. E. Ames ◽  
J. P. Bons
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Rough Surface ◽  
Reynolds Numbers ◽  
Skin Friction Coefficient ◽  
Suction Surface ◽  
Average Roughness ◽  
Surface Distribution ◽  
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%), aero-combustor, (13.5%), and aero-combustor 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 which has accumulated 7500 hours 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 by 573 roughness array generated by Brigham Young on a 9.5 by 5.7 mm region was averaged to a 320 by 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°. 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 [1]. 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 affect on heat transfer in the laminar regions but did cause early transition on the pressure surface in every case.

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

2010 ◽  
Author(s):  
E. L. Erickson ◽  
F. E. Ames ◽  
J. P. Bons
Keyword(s):  
Surface Roughness ◽  
Reynolds Number ◽  
Rough Surface ◽  
Reynolds Numbers ◽  
Grid Turbulence ◽  
Suction Surface ◽  
Trailing Edge ◽  
Average Roughness ◽  
Early Transition ◽  
Aerodynamic Losses

Aerodynamic loss surveys are reported for a vane with a realistically rough surface. Aerodynamic losses are investigated over a range of turbulence levels {low (0.7%), grid (8.5%), aero-combustor, (13.5%)} 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 which has accumulated 7500 hours of operation with a particulate concentration of 0.02 ppmw. The realistically rough surface was scaled by 11 times for consistency with the vane geometry and cast using epoxy to comply with the vane geometry. The surface was applied over the vane pressure surface and about 10% of the suction surface. The 958 by 573 point roughness array generated by Brigham Young on a 9.5 by 5.7 mm region was averaged to a 320 by 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°. 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 [1]. 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. Exit survey measurements for the realistically roughened vane have been compared with the base vane geometry. Total pressure loss measurements have shown an incremental increase above the original base vane which averages 0.68% for the low turbulence, 0.48% for the grid turbulence and 0.24% for the aero-combustor turbulence conditions. A portion of this increment, about 0.20%, could be attributed to the thicker trailing edge due to the average thickness of the roughened tile applied. The roughness on the near suction surface along with the abrupt end of the roughness tiles at about 0.05 m from the stagnation region causes early transition on the suction surface. This early transition influences the comparison of the low turbulence cases much more due to laminar flow on the base vane suction surface. The grid turbulence shows an incremental loss of 0.48% and this difference is likely due to both the thicker trailing edge and the suction surface roughness. The incremental loss increase for the aero-combustor is lower suggesting that the thicker trailing edge has the largest affect on incremental losses.

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.

scholarly journals Predictions for the Effects of Freestream Turbulence on Turbine Blade Heat Transfer

2004 ◽  
Author(s):  
R. J. Boyle ◽  
Forrest E. Ames ◽  
P. W. Giel
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Steady State ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Freestream Turbulence ◽  
Suction Surface ◽  
Pressure Surface ◽  
Wide Range

An approach to predicting the effects of freestream turbulence on turbine vane and blade heat transfer is described. Four models for predicting the effects of freestream turbulence were incorporated into a Navier-Stokes CFD analysis. Predictions were compared with experimental data in order to identify an appropriate model for use across a wide range of flow conditions. The analyses were compared with data from five vane geometries and from four rotor geometries. Each of these nine geometries had data for different Reynolds numbers. Comparisons were made for twenty four cases. Steady state calculations were done because all experimental data were obtained in steady state tests. High turbulence levels often result in suction surface transition upstream of the throat, while at low to moderate Reynolds numbers the pressure surface remains laminar. A two-dimensional analysis was used because the flow is predominantly two-dimensional in the regions where freestream turbulence significantly augments surface heat transfer. Because the evaluation of models for predicting turbulence effects can be affected by other factors, the paper discusses modeling for transition, relaminarization, and near wall damping. Quantitative comparisons are given between the predictions and data.

Heat Transfer to a Pvd Rotor Blade at High Subsonic Passage Throat Mach Numbers

1978 ◽  
Vol 192 (1) ◽  
pp. 225-235 ◽  
Author(s):  
B. W. Martin ◽  
A. Brown ◽  
S. E. Garrett
Keyword(s):  
Heat Transfer ◽  
Rotor Blade ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Suction Surface ◽  
Pressure Surface ◽  
Air Stream ◽  
Mach Numbers

This paper reports heat-transfer measurements round a PVD rotor blade using a transient method. Instrumented syndanio-asbestos blades forming part of a cascade are suddenly introduced into a heated air stream, the temperature-time response of surface thermocouples attached to copper inserts in the blades then being used to determine local heat-transfer coefficients for (a) passage throat Mach numbers between 0.79 and 0.94 (b) turbulence intensities from 4.15 to 9.05 per cent (c) blade chord Reynolds numbers from 7.8 times 105 to 8.9 times 105. Measured transition lengths on the suction surface, over which the heat transfer nearly trebles, are somewhat short in relation to other measurements. The onset of transition, which is downstream of predictions for the higher Reynolds numbers but accords with the trends of existing correlations, is little influenced by turbulence intensity variations in the above range. Over the pressure surface the heat transfer is less than for a fully-turbulent boundary layer. Comparisons with other high Mach-number measurements suggest that much further work is needed before the effects of scale of turbulence are fully understood.

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.

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 Parametric optimization of a stamped longitudinal vortex generator inside a circular tube of a solar water heater at low Reynolds numbers

2021 ◽  
Vol 3 (8) ◽  
Author(s):  
Felipe A. S. Silva ◽  
Luis Júnior ◽  
José Silva ◽  
Sandilya Kambampati ◽  
Leandro Salviano
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Reynolds Numbers ◽  
Geometric Parameters ◽  
Vortex Generators ◽  
Longitudinal Vortex ◽  
Solar Water Heater ◽  
Water Heater ◽  
Solar Water

AbstractSolar Water Heater (SWH) has low efficiency and the performance of this type of device needs to be improved to provide useful and ecological sources of energy. The passive techniques of augmentation heat transfer are an effective strategy to increase the convective heat transfer coefficient without external equipment. In this way, recent investigations have been done to study the potential applications of different inserts including wire coils, vortex generators, and twisted tapes for several solar thermal applications. However, few researchers have investigated inserts in SWH which is useful in many sectors where the working fluid operates at moderate temperatures. The longitudinal vortex generators (LVG) have been applied to promote heat transfer enhancement with a low/moderate pressure drop penalty. Therefore, the present work investigated optimal geometric parameters of LVG to enhance the heat transfer for a SWH at low Reynolds number and laminar flow, using a 3D periodical numerical simulation based on the Finite Volume Method coupled to the Genetic Algorithm optimization method (NSGA-II). The LVG was stamped over a flat plate inserted inside a smooth tube operating under a typical residential application corresponding to Reynolds numbers of 300, 600, and 900. The geometric parameters of LGV were submitted to the optimization procedure which can find traditional LVG such as rectangular-winglet and delta-winglet or a mix of them. The results showed that the application of LGVs to enhance heat transfer is an effective passive technique. The different optimal shapes of the LVG for all Reynolds numbers evaluated improved more than 50% of heat transfer. The highest augmentation heat transfer of 62% is found for the Reynolds number 900. However, the best thermo-hydraulic efficiency value is found for the Reynolds number of 600 in which the heat transfer intensification represents 55% of the pressure drop penalty.

Heat transfer enhancement using second mode self-oscillating structures

2019 ◽  
Vol 30 (7) ◽  
pp. 3827-3842
Author(s):  
Samer Ali ◽  
Zein Alabidin Shami ◽  
Ali Badran ◽  
Charbel Habchi
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Laminar Flow ◽  
Flow Regime ◽  
Vortex Generator ◽  
Reynolds Numbers ◽  
Content Type ◽  
Laminar Flow Regime ◽  
Second Mode

Purpose In this paper, self-sustained second mode oscillations of flexible vortex generator (FVG) are produced to enhance the heat transfer in two-dimensional laminar flow regime. The purpose of this study is to determine the critical Reynolds number at which FVG becomes more efficient than rigid vortex generators (RVGs). Design/methodology/approach Ten cases were studied with different Reynolds numbers varying from 200 to 2,000. The Nusselt number and friction coefficients of the FVG cases are compared to those of RVG and empty channel at the same Reynolds numbers. Findings For Reynolds numbers higher than 800, the FVG oscillates in the second mode causing a significant increase in the velocity gradients generating unsteady coherent flow structures. The highest performance was obtained at the maximum Reynolds number for which the global Nusselt number is improved by 35.3 and 41.4 per cent with respect to empty channel and rigid configuration, respectively. Moreover, the thermal enhancement factor corresponding to FVG is 72 per cent higher than that of RVG. Practical implications The results obtained here can help in the design of novel multifunctional heat exchangers/reactors by using flexible tabs and inserts instead of rigid ones. Originality/value The originality of this paper is the use of second mode oscillations of FVG to enhance heat transfer in laminar flow regime.

Heat Transfer for High Aspect Ratio Rectangular Channels in a Stationary Serpentine Passage With Turbulated and Smooth Surfaces

2013 ◽  
Author(s):  
Matthew A. Smith ◽  
Randall M. Mathison ◽  
Michael G. Dunn
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Aspect Ratio ◽  
Flow Behavior ◽  
Reynolds Numbers ◽  
Hydraulic Diameter ◽  
Internal Cooling ◽  
Number Range ◽  
Aspect Ratios ◽  
Parallel Configuration

Heat transfer distributions are presented for a stationary three passage serpentine internal cooling channel for a range of engine representative Reynolds numbers. The spacing between the sidewalls of the serpentine passage is fixed and the aspect ratio (AR) is adjusted to 1:1, 1:2, and 1:6 by changing the distance between the top and bottom walls. Data are presented for aspect ratios of 1:1 and 1:6 for smooth passage walls and for aspect ratios of 1:1, 1:2, and 1:6 for passages with two surfaces turbulated. For the turbulated cases, turbulators skewed 45° to the flow are installed on the top and bottom walls. The square turbulators are arranged in an offset parallel configuration with a fixed rib pitch-to-height ratio (P/e) of 10 and a rib height-to-hydraulic diameter ratio (e/Dh) range of 0.100 to 0.058 for AR 1:1 to 1:6, respectively. The experiments span a Reynolds number range of 4,000 to 130,000 based on the passage hydraulic diameter. While this experiment utilizes a basic layout similar to previous research, it is the first to run an aspect ratio as large as 1:6, and it also pushes the Reynolds number to higher values than were previously available for the 1:2 aspect ratio. The results demonstrate that while the normalized Nusselt number for the AR 1:2 configuration changes linearly with Reynolds number up to 130,000, there is a significant change in flow behavior between Re = 25,000 and Re = 50,000 for the aspect ratio 1:6 case. This suggests that while it may be possible to interpolate between points for different flow conditions, each geometric configuration must be investigated independently. The results show the highest heat transfer and the greatest heat transfer enhancement are obtained with the AR 1:6 configuration due to greater secondary flow development for both the smooth and turbulated cases. This enhancement was particularly notable for the AR 1:6 case for Reynolds numbers at or above 50,000.

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