The Effect of Side Wall Mass Extraction on Pressure Loss and Heat Transfer of a Ribbed Rectangular Two-Pass Internal Cooling Channel

2010 ◽  
Vol 133 (2) ◽  
Author(s):  
Marco Schüler ◽  
Frank Zehnder ◽  
Bernhard Weigand ◽  
Jens von Wolfersdorf ◽  
Sven Olaf Neumann
Keyword(s):  
Heat Transfer ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Pressure Loss ◽  
Side Wall ◽  
Internal Cooling ◽  
Cooling Channel ◽  
Trailing Edge ◽  
Wall Mass

Gas turbine blades are often cooled by using combined internal and external cooling methods where for internal cooling purposes, usually, serpentine passages are applied. In order to optimize the design of these serpentine passages it is inevitable to know the influence of mass extraction due to film cooling holes, dust holes, or due to side walls for feeding successive cooling channels as for the trailing edge on the internal cooling performance. Therefore, the objective of the present study was to analyze the influence of side wall mass extraction on pressure loss and heat transfer distribution in a two-pass internal cooling channel representing a cooling scheme with flow towards the trailing edge. The investigated rectangular two-pass channel consisted of an inlet and outlet duct with a height-to-width ratio of H/W=2 connected by a 180 deg sharp bend. The tip-to-web distance was kept constant at Wel/W=1. The mass extraction was realized using several circular holes in the outlet pass side wall. Two geometric configurations were investigated: A configuration with mass extraction solely in the outlet pass and a configuration with mass extraction in the bend region and outlet pass. The extracted mass flow rate was 0%, 10%, and 20% of the inlet channel mass flow. Spatially resolved heat transfer distributions were obtained using the transient thermochromic liquid crystal technique. Pressure losses were determined in separate experiments by local static pressure measurements. Furthermore, a computational study was performed solving the Reynolds-averaged Navier–Stokes equations using the commercial finite-volume solver FLUENT. The numerical grids were generated using the hybrid grid generator CENTAUR. Three different turbulence models were considered: the realizable k-ε model with two-layer wall treatment, the k-ω-SST model, and the v2-f model. The experimental data of the investigation of side wall ejection showed that the heat transfer in the bend region slightly increased when the ejection were in operation, while the heat transfer in the section of the outlet channel with side wall ejection was nearly not affected. After this section, a decrease in heat transfer was observed, which can be attributed to the decreased mainstream mass flow rate.

The Effect of Side Wall Mass Extraction on Pressure Loss and Heat Transfer of a Ribbed Rectangular Two-Pass Internal Cooling Channel

2009 ◽  
Author(s):  
Marco Schu¨ler ◽  
Frank Zehnder ◽  
Bernhard Weigand ◽  
Jens von Wolfersdorf ◽  
Sven Olaf Neumann
Keyword(s):  
Heat Transfer ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Pressure Loss ◽  
Side Wall ◽  
Internal Cooling ◽  
Cooling Channel ◽  
Trailing Edge ◽  
Wall Mass

Gas turbine blades are often cooled by using combined internal and external cooling methods, where for internal cooling purposes usually serpentine passages are applied. In order to optimize the design of these serpentine passages it is inevitable to know the influence of mass extraction due to film cooling holes, dust holes or due to side walls for feeding successive cooling channels as for the trailing edge on the internal cooling performance. Therefore, the objective of the present study was to analyse the influence of side wall mass extraction on pressure loss and heat transfer distribution in a two-pass internal cooling channel representing a cooling scheme with flow towards the trailing edge. The investigated rectangular two-pass channel consisted of an inlet and outlet duct with a height-to-width ratio of H/W = 2 connected by a 180° sharp bend. The tip-to-web distance was kept constant at Wel/W = 1. The mass extraction was realized using several circular holes in the outlet pass side wall. Two geometric configurations were investigated: A configuration with mass extraction solely in the outlet pass, and a configuration with mass extraction in the bend region and outlet pass. The extracted mass flow rate was 0%, 10%, and 20% of the inlet channel mass flow. Spatially resolved heat transfer distributions were obtained using the transient thermochromic liquid crystal technique. Pressure losses were determined in separate experiments by local static pressure measurements. Furthermore, a computational study was performed solving the Reynolds-Averaged Navier-Stokes equations (RANS method) using the commercial Finite-Volume solver FLUENT. The numerical grids were generated using the hybrid grid generator CENTAUR. Three different turbulence models were considered: the realizable k-ε model with two-layer wall treatment, the k-ω-SST model, and the v2-f model. The experimental data of the investigation of side wall ejection showed that the heat transfer in the bend region slightly increased when the ejection was in operation, while the heat transfer in the section of the outlet channel with side wall ejection was nearly not affected. After this section a decrease in heat transfer was observed which can be attributed to the decreased mainstream mass flow rate.

Heat Transfer in a Two-Inlet Rotating Pin-Fin Roughened Rectangular Channel With Side-Wall Fluid Extraction

2018 ◽  
Author(s):  
Yanan Chen ◽  
Jie Wen ◽  
Guoqiang Xu ◽  
Zhiliang Du ◽  
Yunqing Dai
Keyword(s):  
Heat Transfer ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Rectangular Channel ◽  
Side Wall ◽  
Flow Rate Ratio ◽  
Cooling Channel ◽  
Inlet Channel ◽  
Pin Fin

The heat transfer characteristics in a rotating pin-fin roughened rectangular channel with an aspect ratio of 4:1 is investigated, simulating a rotor blade trailing edge. The copper plate regional average method is used to determine the heat transfer coefficient. A second inlet is added at the inner top corner of the traditional one-inlet cooling channel to improve heat transfer in the high radius region. Coolant from these two inlets mixes in the middle of the channel, and then exits through eight sidewall slots. The channel is assembled in a rotating facility, and the symmetrical plane of the rectangular channel is orientated at an angle of 135° with respect to the rotation plane. The mass flow rate of the bottom inlet is kept at a constant (Re1 = 20,000), whereas the inlet mass flow rate ratio (MR, second inlet mass flow rate/bottom inlet mass flow rate) changes from 0 to around 0.55. Results show that the second inlet improves the heat transfer in the proximity of the second inlet extensively, but the overall averaged heat transfer is decreased a bit compared to the one inlet channel. Moreover, with the local MR, the heat transfer data at different locations converge into the same trend, indicating that the local MR should be a good parameter in describing the flow in this pin-fin cooling channel. In the rotating one-inlet channel (MR = 0), a critical Ro phenomenon is observed. After the critical point, rotation stops decreasing heat transfer and starts to elevate it. A lower critical Ro is observed at higher radius location but the corresponding local Ro is a constant at around 1.0. In rotating two-inlet channel, the overall heat transfer enhancement caused by rotation is almost in the same level with different MR, indicating that high MR cases (MR > 0.2) is not recommended because the coolant from the second inlet is not efficiently used.

scholarly journals Effect of Reynolds Number and Property Variation on Fluid Flow and Heat Transfer in the Entrance Region of a Turbine Blade Internal-Cooling Channel

2005 ◽  
Vol 2005 (1) ◽  
pp. 36-44 ◽  
Author(s):  
R. Ben-Mansour ◽  
L. Al-Hadhrami
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Mass Flow Rate ◽  
Heat Transfer Rate ◽  
Turbine Blade ◽  
Flow Rate ◽  
Transfer Rate ◽  
Internal Cooling ◽  
Cooling Channel ◽  
Flow And Heat Transfer

Internal cooling is one of the effective techniques to cool turbine blades from inside. This internal cooling is achieved by pumping a relatively cold fluid through the internal-cooling channels. These channels are fed through short channels placed at the root of the turbine blade, usually called entrance region channels. The entrance region at the root of the turbine blade usually has a different geometry than the internal-cooling channel of the blade. This study investigates numerically the fluid flow and heat transfer in one-pass smooth isothermally heated channel using the RNGk−εmodel. The effect of Reynolds number on the flow and heat transfer characteristics has been studied for two mass flow rate ratios (1/1and1/2) for the same cooling channel. The Reynolds number was varied between10 000and50 000. The study has shown that the cooling channel goes through hydrodynamic and thermal development which necessitates a detailed flow and heat transfer study to evaluate the pressure drop and heat transfer rates. For the case of unbalanced mass flow rate ratio, a maximum difference of8.9% in the heat transfer rate between the top and bottom surfaces occurs atRe=10 000while the total heat transfer rate from both surfaces is the same for the balanced mass flow rate case. The effect of temperature-dependent property variation showed a small change in the heat transfer rates when all properties were allowed to vary with temperature. However, individual effects can be significant such as the effect of density variation, which resulted in as much as9.6% reduction in the heat transfer rate.

Numerical and Experimental Investigation of Turning Flow Effects on Innovative Pin Fin Arrangements for Trailing Edge Cooling Configurations

2010 ◽  
Author(s):  
C. Bianchini ◽  
B. Facchini ◽  
F. Simonetti ◽  
L. Tarchi ◽  
S. Zecchi
Keyword(s):  
Heat Transfer ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Surface Flow ◽  
Point Of View ◽  
Experimental Point ◽  
Outlet Section ◽  
Trailing Edge ◽  
Tip Mass

The effect of the array configuration of circular pin-fins is investigated from a numerical and experimental point of view reproducing a typical cooling scheme of a real high pressure aeroengine blade. The airstream enters the domain of interest radially from the hub inlet and exits axially from the trailing edge (TE) outlet section. More than one hundred turbulators are inserted in the wedge shaped TE duct to enhance the heat transfer: a reference array implementing 7 rows of staggered pins is compared with an innovative pentagonal arrangement. Investigations were made considering real engine flow conditions: both numerical calculations and experimental measurements were performed fixing Re = 18000 and Ma = 0.3 in the TE throat section. The effect of the tip mass flow rate was also taken into account, investigating 0% and 25% of the TE mass flow rate. The experimental activity was aimed at obtaining detailed heat transfer coefficient maps over the internal pressure side (PS) surface by means of the transient technique with thermochromic liquid crystals. Particle Image Velocimetry measurements were performed and surface flow visualizations were made by means of the oil & dye technique on the PS surface. Steady-state RANS simulations were performed with two different CFD codes: the commercial software Ansys CFX® 11.0 and an in-house solver based on the opensource toolbox OpenFOAM®, to compare the performance and predictive capabilities. Turbulence was modeled by means of the k–ω SST model with an hybrid near wall treatment allowing strong clustering of the wall of interest as well as quite coarse refinement on the other viscous surfaces.

Experimental/Numerical Investigation on the Effects of Trailing-Edge Cooling Hole Blockage on Heat Transfer in a Trailing-Edge Cooling Channel

2013 ◽  
Author(s):  
M. E. Taslim ◽  
X. Huang
Keyword(s):  
Heat Transfer ◽  
Mass Flow Rate ◽  
Turbulence Model ◽  
Mass Flow ◽  
Flow Rate ◽  
Transfer Coefficients ◽  
Trailing Edge ◽  
Edge Channel ◽  
Heat Transfer Coefficients ◽  
Near Wall

Hot and harsh environments, sometimes experienced by gas turbine airfoils, can create undesirable effects such as clogging of the cooling holes. Clogging of the cooling holes along the trailing edge of an airfoil on the tip side and its effects on the heat transfer coefficients in the cooling cavity around the clogged holes is the main focus of this investigation. Local and average heat transfer coefficients were measured in a test section simulating a rib-roughened trailing edge cooling cavity of a turbine airfoil. The rig was made up of two adjacent channels, each with a trapezoidal cross sectional area. The first channel supplied the cooling air to the trailing-edge channel through a row of racetrack-shaped slots on the partition wall between the two channels. Eleven cross-over jets, issued from these slots entered the trailing-edge channel, impinged on eleven radial ribs and exited from a second row of race-track shaped slots on the opposite wall that simulated the cooling holes along the trailing edge of the airfoil. Tests were run for the baseline case with all exit holes open and for cases in which 2, 3 and 4 exit holes on the airfoil tip side were clogged. All tests were run for two cross-over jet angles. The first set of tests were run for zero angle between the jet axis and the trailing-edge channel centerline. The jets were then tilted towards the ribs by five degrees. Results of the two set of tests for a range of jet Reynolds number from 10,000 to 35,000 were compared. The numerical models contained the entire trailing-edge and supply channels with all slots and ribs to simulate exactly the tested geometries. They were meshed with all-hexa structured mesh of high near-wall concentration. A pressure-correction based, multi-block, multi-grid, unstructured/adaptive commercial software was used in this investigation. The realizable k – ε turbulence model in combination with enhanced wall treatment approach for the near wall regions were used for turbulence closure. Boundary conditions identical to those of the experiments were applied and several turbulence model results were compared. The numerical analyses also provided the share of each cross-over and each exit hole from the total flow for different geometries. The major conclusions of this study were: a) Clogging of the exit holes near the airfoil tip alters the distribution of the coolant mass flow rate through the crossover holes and changes the flow structure. Depending on the number of clogged exit holes (from 3 to 6, out of 12), the tip-end crossover hole experienced from 35% to 49% reductions in its mass flow rate while the root-end crossover hole, under the same conditions, experienced an increase of the same magnitude in its mass flow rate, b) up to 64% reduction in heat transfer coefficients on the tip-end surface areas around the clogged holes were observed which might have devastating effects on the airfoil life. At the same time, a gain in heat transfer coefficient of up 40% was observed around the root-end due to increased crossover flows, c) Numerical heat transfer results with the use of the realizable k – ε turbulence model in combination with enhanced wall treatment approach for the near wall regions were generally in a reasonable agreement with the test results. The overall difference between the CFD and test results was about 10%.

Heat Transfer, Pressure Drop, and Mass Flow Rate in Pin Fin Channels With Long and Short Trailing Edge Ejection Holes

1989 ◽  
Vol 111 (2) ◽  
pp. 116-123 ◽  
Author(s):  
S. C. Lau ◽  
J. C. Han ◽  
T. Batten
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Radial Flow ◽  
Trailing Edge ◽  
Test Channel ◽  
Pin Fin ◽  
Edge Flow

Experiments have been conducted to study the turbulent heat transfer and friction characteristics in pin fin channels with small trailing edge ejection holes that are commonly found in modern internally cooled turbine airfoils. The main objective of the investigation is to examine the effects of varying the length and the configuration of the trailing edge ejection holes on the overall heat transfer, the overall pressure drop, the local pressure distribution, and the local mass flow rate distribution in the pin fin channel. The staggered pin fin array (L/D = 1.0, X/D = S/D = 2.5) in the test channel has 15 rows of three pins. The diameter of the ejection holes is one-half the diameter of the pins. There are 30 or 23 ejection holes on one of the side walls of the test channel and six similar ejection holes at the radial flow exit. Experimental results are obtained for two trailing edge ejection hole lengths, four ejection hole configurations, and Reynolds numbers between 10,000 and 60,000. The results show that the overall heat transfer increases when the length of the trailing edge ejection holes is increased and when the trailing edge ejection holes are configured so that much of the cooling air is forced to flow farther downstream in the radial flow direction before exiting the pin fin channel through ejection holes. The overall Nusselt number can be correlated with an equation of the form NuD = a (ReD)b, where the values of the exponent b are about the same for all the test cases with trailing edge flow ejection. Results also show that the increase in the overall heat transfer is generally accompanied by an increase in the overall pressure drop (that is, an increase in the required pumping power), except that the overall heat transfer is lower and the overall pressure drop is higher when there is no radial flow ejection. In the cases with both radial and trailing edge flow ejection, about 15 to 20 percent of the flow exits through the tip bleed holes.

Numerical and Experimental Investigation of Turning Flow Effects on Innovative Pin Fin Arrangements for Trailing Edge Cooling Configurations

2011 ◽  
Vol 134 (2) ◽  
Author(s):  
C. Bianchini ◽  
B. Facchini ◽  
F. Simonetti ◽  
L. Tarchi ◽  
S. Zecchi
Keyword(s):  
Heat Transfer ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Surface Flow ◽  
Point Of View ◽  
Experimental Point ◽  
Outlet Section ◽  
Trailing Edge ◽  
Tip Mass

The effect of the array configuration of circular pin fins is investigated from a numerical and experimental point of view reproducing a typical cooling scheme of a real high pressure aero-engine blade. The airstream enters the domain of interest radially from the hub inlet and exits axially from the trailing edge (TE) outlet section. More than 100 turbulators are inserted in the wedge-shaped TE duct to enhance the heat transfer: A reference array implementing seven rows of staggered pins is compared with an innovative pentagonal arrangement. Investigations were made considering real engine flow conditions: Both numerical calculations and experimental measurements were performed fixing Re=18,000 and Ma=0.3 in the TE throat section. The effect of the tip mass flow rate was also taken into account, investigating 0% and 25% of the TE mass flow rate. The experimental activity was aimed at obtaining detailed heat transfer coefficient maps over the internal pressure side (PS) surface by means of the transient technique with thermochromic liquid crystals. Particle image velocimetry measurements were performed and surface flow visualizations were made by means of the oil and dye technique on the PS surface. Steady-state Reynolds averaged Navier–Stokes simulations were performed with two different computational fluid dynamics (CFD) codes: the commercial software Ansys CFX®11.0 and an in-house solver based on the opensource toolbox OpenFOAM®, to compare the performance and predictive capabilities. Turbulence was modeled by means of the k−ω shear stress transport (SST) model with a hybrid near-wall treatment allowing strong clustering of the wall of interest as well as quite coarse refinement on the other viscous surfaces.

Experimental/Numerical Investigation on the Effects of Trailing-Edge Cooling Hole Blockage on Heat Transfer in a Trailing-Edge Cooling Channel

2014 ◽  
Vol 136 (8) ◽  
Author(s):  
M. E. Taslim ◽  
X. Huang
Keyword(s):  
Heat Transfer ◽  
Mass Flow Rate ◽  
Turbulence Model ◽  
Mass Flow ◽  
Flow Rate ◽  
Transfer Coefficients ◽  
Trailing Edge ◽  
Edge Channel ◽  
Heat Transfer Coefficients ◽  
Near Wall

Hot and harsh environments, sometimes experienced by gas turbine airfoils, can create undesirable effects such as clogging of the cooling holes. Clogging of the cooling holes along the trailing edge of an airfoil on the tip side and its effects on the heat transfer coefficients in the cooling cavity around the clogged holes is the main focus of this investigation. Local and average heat transfer coefficients were measured in a test section simulating a rib-roughened trailing edge cooling cavity of a turbine airfoil. The rig was made up of two adjacent channels, each with a trapezoidal cross sectional area. The first channel supplied the cooling air to the trailing-edge channel through a row of racetrack-shaped slots on the partition wall between the two channels. Eleven crossover jets, issued from these slots entered the trailing-edge channel, impinged on eleven radial ribs and exited from a second row of race-track shaped slots on the opposite wall that simulated the cooling holes along the trailing edge of the airfoil. Tests were run for the baseline case with all exit holes open and for cases in which 2, 3, and 4 exit holes on the airfoil tip side were clogged. All tests were run for two crossover jet angles. The first set of tests were run for zero angle between the jet axis and the trailing-edge channel centerline. The jets were then tilted towards the ribs by five degrees. Results of the two set of tests for a range of jet Reynolds number from 10,000 to 35,000 were compared. The numerical models contained the entire trailing-edge and supply channels with all slots and ribs to simulate exactly the tested geometries. They were meshed with all-hexa structured mesh of high near-wall concentration. A pressure-correction based, multiblock, multigrid, unstructured/adaptive commercial software was used in this investigation. The realizable k-ε turbulence model in combination with enhanced wall treatment approach for the near wall regions were used for turbulence closure. Boundary conditions identical to those of the experiments were applied and several turbulence model results were compared. The numerical analyses also provided the share of each crossover and each exit hole from the total flow for different geometries. The major conclusions of this study were: (a) clogging of the exit holes near the airfoil tip alters the distribution of the coolant mass flow rate through the crossover holes and changes the flow structure. Depending on the number of clogged exit holes (from 3 to 6, out of 12), the tip-end crossover hole experienced from 35% to 49% reductions in its mass flow rate while the root-end crossover hole, under the same conditions, experienced an increase of the same magnitude in its mass flow rate. (b) Up to 64% reduction in heat transfer coefficients on the tip-end surface areas around the clogged holes were observed which might have devastating effects on the airfoil life. At the same time, a gain in heat transfer coefficient of up 40% was observed around the root-end due to increased crossover flows. (c) Numerical heat transfer results with the use of the realizable k-ε turbulence model in combination with enhanced wall treatment approach for the near wall regions were generally in a reasonable agreement with the test results. The overall difference between the CFD and test results was about 10%.

Effect of pre-swirl nozzle closure modes on unsteady flow and heat transfer characteristics in a pre-swirl system of aero-engine

2021 ◽  
pp. 095441002110191
Author(s):  
Gaowen Liu ◽  
Zhao Lei ◽  
Aqiang Lin ◽  
Qing Feng ◽  
Yan Chen
Keyword(s):  
Heat Transfer ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Temperature Drop ◽  
Thermodynamic Characteristics ◽  
Circumferential Direction ◽  
Temperature Changes ◽  
Air Supply ◽  
Cooling Air

The pre-swirl system is of great importance for temperature drop and cooling air supply. This study aims to investigate the influencing mechanism of heat transfer, nonuniform thermodynamic characteristics, and cooling air supply sensitivity in a pre-swirl system by the application of the flow control method of the pre-swirl nozzle. A novel test rig was proposed to actively control the supplied cooling air mass flow rate by three adjustable pre-swirl nozzles. Then, the transient problem of the pre-swirl system was numerically conducted by comparison with 60°, 120°, and 180° rotating disk cavity cases, which were verified with the experiment results. Results show that the partial nozzle closure will aggravate the fluctuation of air supply mass flow rate and temperature. When three parts of nozzles are closed evenly at 120° in the circumferential direction, the maximum value of the nonuniformity coefficient of air supply mass flow rate changes to 3.1% and that of temperature changes to 0.25%. When six parts of nozzles are closed evenly at 60° in the circumferential direction, the maximum nonuniformity coefficient of air supply mass flow rate changes to 1.4% and that of temperature changes to 0.20%. However, different partial nozzle closure modes have little effect on the average air supply parameters. Closing 14.3% of the nozzle area will reduce the air supply mass flow rate by 9.9% and the average air supply temperature by about 1 K.

Heat Transfer and Pressure Drop in a Converging Pedestal Array With Exit Area Variation

2018 ◽  
Author(s):  
L. W. Soma ◽  
F. E. Ames ◽  
S. Acharya
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Rate ◽  
Film Cooling ◽  
Reynolds Numbers ◽  
Flow Path ◽  
Internal Cooling ◽  
Channel Measurements ◽  
Trailing Edge ◽  
Cooling Air

The trailing edge of a vane is one of the most difficult areas to cool due to a narrowing flow path, high external heat transfer rates, and deteriorating external film cooling protection. Converging pedestal arrays are often used as a means to provide internal cooling in this region. The thermally induced stresses in the trailing edge region of these converging arrays have been known to cause failure in the pedestals of conventional solidity arrays. The present paper documents the heat transfer and pressure drop through two high solidity converging rounded diamond pedestal arrays. These arrays have a 45 percent pedestal solidity. One array which was tested has nine rows of pedestals with an exit area in the last row consistent with the convergence. The other array has eight rows with an expanded exit in the last row to enable a higher cooling air flow rate. The expanded exit of the eight row array allows a 30% increase in the coolant flow rate compared with the nine row array for the same pressure drop. Heat transfer levels correlate well based on local Reynolds numbers but fall slightly below non converging arrays. The pressure drop across the array naturally increases toward the trailing edge with the convergence of the flow passage. A portion of the cooling air pressure drop can be attributed to acceleration while a portion can be attributed to flow path losses. Detailed array static pressure measurements provide a means to develop a correlation for the prediction of pressure drop across the cooling channel. Measurements have been acquired over Reynolds numbers based on exit flow conditions and the characteristic pedestal length scale ranging from 5000 to over 70,000.

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