Experimental Racetrack Shaped Jet Impingement on a Roughened Leading-Edge Wall With Film Holes

2002 ◽  
Author(s):  
M. E. Taslim ◽  
Y. Pan ◽  
K. Bakhtari
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Leading Edge ◽  
Jet Impingement ◽  
Target Surface ◽  
Cross Sectional ◽  
Impingement Heat Transfer ◽  
Circular Jets ◽  
Edge Surface

Compatible with the external contour of the turbine airfoils at their leading edge, the leading-edge cooling cavities have a complex cross-sectional shape. To enhance the heat transfer coefficient on the leading-edge wall of these cavities, the cooling flow in some designs enters the leading-edge cavity from the adjacent cavity through a series of crossover holes on the partition wall between the two cavities. The crossover jets then impinge on the concave leading-edge wall and exit through the showerhead film holes, gill film holes on the pressure and suction sides, and, in some cases, form a crossflow in the leading-edge cavity and move toward the airfoil tip. The main objective of this investigation was to study the effects that racetrack crossover jets, in the presence of film holes on the target surface, have on the impingement heat transfer coefficient. Available data in open literature are mostly for impingement on a flat smooth surface with no representation of the film holes. This investigation covered new features in airfoil leading-edge cooling concept such as impingement with racetrack shaped holes on a roughened target surface with a row of holes representing the leading-edge showerhead film holes. Results of the circular crossover jets impinging on these leading-edge surface geometries with and without showerhead holes were reported by these authors previously. In this paper, however, the experimental results are presented for the impingement of racetrack-shaped crossover jets on a concave surface with showerhead film holes. The investigated target surface geometries were : (1) a smooth wall, (2) a wall roughened with big conical bumps, (3) a wall roughened with smaller conical bumps and (4) a wall roughened with tapered radial ribs. The tests were run for a range of flow arrangements and jet Reynolds numbers and the results were compared with those of round crossover jets. The major conclusions of this study are: (a) for a given jet Reynolds number, the racetrack crossover jets produce a higher impingement heat transfer coefficient than the circular jets, (b) the overall heat transfer performance of 0° racetrack crossover jets is superior to that of 45° racetrack crossover jets and (c) there is a heat transfer enhancement benefit in roughening the target surface. With the presence of showerhead holes, the enhancement is due to both the impingement heat transfer coefficient and the heat transfer area increase.

An Experimental Study of Impingement on Roughened Airfoil Leading-Edge Walls With Film Holes

2001 ◽  
Vol 123 (4) ◽  
pp. 766-773 ◽  
Author(s):  
M. E. Taslim ◽  
Y. Pan ◽  
S. D. Spring
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Gas Turbines ◽  
Heat Removal ◽  
Leading Edge ◽  
Target Surface ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Impingement Heat Transfer

Airfoil leading-edge surfaces in state-of-the-art gas turbines, being exposed to very high gas temperatures, are often life-limiting locations and require complex cooling schemes for robust designs. A combination of convection and film cooling is used in conventional designs to maintain leading-edge metal temperatures at levels consistent with airfoil life requirements. Compatible with the external contour of the airfoil at the leading edge, the leading-edge cooling cavities often have complex cross-sectional shapes. Furthermore, to enhance the heat transfer coefficient in these cavities, they are often roughened on three walls with ribs of different geometries. The cooling flow for these geometries usually enters the cavity from the airfoil root and flows radially to the airfoil tip or, in the more advanced designs, enters the leading edge cavity from the adjacent cavity through a series of crossover holes in the wall separating the two cavities. In the latter case, the crossover jets impinge on a smooth leading-edge wall and exit through the showerhead film holes, gill film holes on the pressure and suction sides, and, in some cases, form a crossflow in the leading-edge cavity, which is ejected through the airfoil tip hole. The main objective of this investigation was to study the effects that film holes on the target surface have on the impingement heat transfer coefficient. Available data in the open literature are mostly for impingement on a flat smooth surface with no representation of the film holes. This investigation involved two new features used in airfoil leading-edge cooling, those being a curved and roughened target surface in conjunction with leading-edge row of film holes. Results of the crossover jets impinging on these leading-edge surface geometries with no film holes were reported by these authors previously. This paper reports experimental results of crossover jets impinging on those same geometries in the presence of film holes. The investigated surface geometries were smooth, roughened with large and small conical bumps as well as tapered radial ribs. A range of flow arrangements and jet Reynolds numbers were investigated, and the results were compared to those of the previous study where no film holes were present. It was concluded that the presence of leading-edge film holes along the leading edge enhances the internal impingement heat transfer coefficients significantly. The smaller conical bump geometry in this investigation produced impingement heat transfer coefficients up to 35 percent higher than those of the smooth target surface. When the contribution of the increased area in the overall heat transfer is taken into consideration, this same geometry for all flow cases as well as jet impingement distances Z/djet provides an increase in the heat removal from the target surface by as much as 95 percent when compared with the smooth target surface.

An Experimental Study of Impingement on Roughened Airfoil Leading-Edge Walls With Film Holes

2001 ◽  
Author(s):  
M. E. Taslim ◽  
Y. Pan ◽  
S. D. Spring
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Gas Turbines ◽  
Heat Removal ◽  
Leading Edge ◽  
Target Surface ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Impingement Heat Transfer

Airfoil leading-edge surfaces in state-of-the-art gas turbines, being exposed to very high gas temperatures, are often life-limiting locations and require complex cooling schemes for robust designs. A combination of convection and film cooling is used in conventional designs to maintain leading-edge metal temperatures at levels consistent with airfoil life requirements. Compatible with the external contour of the airfoil at the leading edge, the leading-edge cooling cavities often have complex cross-sectional shapes. Furthermore, to enhance the heat transfer coefficient in these cavities, they are often roughened on three walls with ribs of different geometries. The cooling flow for these geometries usually enters the cavity from the airfoil root and flows radially to the airfoil tip or, in the more advanced designs, enters the leading edge cavity from the adjacent cavity through a series of crossover holes in the wall separating the two cavities. In the latter case, the crossover jets impinge on a smooth leading-edge wall and exit through the showerhead film holes, gill film holes on the pressure and suction sides, and, in some cases, forms a cross-flow in the leading-edge cavity and is ejected through the airfoil tip hole. The main objective of this investigation was to study the effects that film holes on the target surface have on the impingement heat transfer coefficient. Available data in the open literature are mostly for impingement on a flat smooth surface with no representation of the film holes. This investigation involved two new features used in airfoil leading-edge cooling those being a curved and roughened target surface in conjunction with leading-edge row of film holes. Results of the crossover jets impinging on these leading-edge surface geometries with no film holes were reported by these authors previously. This paper reports experimental results of crossover jets impinging on those same geometries in the presence of film holes. The investigated surface geometries were smooth, roughened with large and small conical bumps as well as tapered radial ribs. A range of flow arrangements and jet Reynolds numbers were investigated and the results were compared to those of the previous study were no film holes were present. It was concluded that the presence of leading-edge film holes along the leading edge enhances the internal impingement heat transfer coefficients significantly. The smaller conical bump geometry in this investigation produced impingement heat transfer coefficients up to 35% higher than those of the smooth target surface. When the contribution of the increased area in the overall heat transfer is taken into consideration, this same geometry for all flow cases as well as jet impingement distances (Z/djet) provides an increase in the heat removal from the target surface by as much as 95% when compared with the smooth target surface.

Experimental Investigation of Crossflow Diverters in Jet Impingement Cooling

2019 ◽  
Author(s):  
Srivatsan Madhavan ◽  
Kishore Ranganath Ramakrishnan ◽  
Prashant Singh ◽  
Srinath V. Ekkad
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Turbine Blades ◽  
Jet Impingement ◽  
Target Surface ◽  
Pumping Power ◽  
Detailed Measurement ◽  
To Come

Abstract Jet impingement is a cooling technique commonly employed in combustor liner cooling and high-pressure gas turbine blades. However, jets from upstream impingement holes reduce the effectiveness of downstream jets due to jet deflection in the direction of crossflow. In order to avoid this phenomenon and provide an enhanced cooling on the target surface, we have attempted to come up with a novel design called “crossflow diverters”. Crossflow diverters are U-shaped ribs that are placed between jets in the crossflow direction (under maximum crossflow condition). In this study, the baseline case is jet impingement onto a smooth surface with 10 rows of jet impingement holes, jet-to-jet spacing of X/D = Y/D = 6 and jet-to-target spacing of Z/D = 2. Crossflow diverters with thickness ‘t’ of 1.5875 mm, height ‘h’ of 2D placed in the streamwise direction at a distance of X = 2D from center of the jet have been investigated experimentally. Transient liquid crystal thermography technique has been used to obtain detailed measurement of heat transfer coefficient for four jet diameter based Reynolds numbers of 3500, 5000, 7500, 12000. It has been observed that crossflow diverters protect the downstream jets from upstream jet deflection thereby maximizing their stagnation cooling potential. An average of 15–30% enhancement in Nusselt number is obtained over the flow range tested. However, this comes at the expense of increase in pumping power. Pressure drop for the enhanced geometry is 1–1.5 times the pressure drop for baseline impingement case. At a constant pumping power, crossflow diverters produce 9–15% enhancement in heat transfer coefficient as compared to baseline smooth case.

Impingement Heat Transfer of Various Lobe-Shaped Nozzles

2019 ◽  
Author(s):  
Sanskar S. Panse ◽  
Srivatsan Madhavan ◽  
Prashant Singh ◽  
Srinath V. Ekkad
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Transfer Performance ◽  
Convective Heat Transfer Coefficient ◽  
Transfer Performance ◽  
Impingement Heat Transfer ◽  
Circular Jets ◽  
Contour Plots ◽  
Drastic Effect

Abstract This paper presents heat transfer characteristics of lobed nozzles, three different lobe configurations viz. three-, four- and six-lobe jets have been tested over a range of Reynolds numbers (based on the effective jet diameter, de) between 8000 and 16000 and normalized jet-to-target spacings (z/de) of 1.6, 3.2 and 4.8. The heat transfer results of lobed configurations were compared to the baseline configuration of circular jets. Steady-state infrared thermography (IRT) experiments were carried out for convective heat transfer coefficient calculations. Experimental results show that the three lobe configuration has a superior heat transfer performance compared to other configurations. Jet-to-target plate standoff distance had drastic effect on the heat transfer performance and contour plots for the lobed nozzles, as heat transfer performance diminished with increase in z/de. For the lobe configurations, with increase in jet-to-target spacing (z/de), the heat transfer coefficient maps tend towards a more circular profile due to the effect of jet diffusion.

Impingement Heat Transfer Enhancement on a Cylindrical, Leading Edge Model With Varying Jet Temperatures

2012 ◽  
Author(s):  
Evan L. Martin ◽  
Lesley M. Wright ◽  
Daniel C. Crites
Keyword(s):  
Heat Transfer ◽  
Experimental Technique ◽  
Leading Edge ◽  
Jet Impingement ◽  
Target Surface ◽  
Large Temperature ◽  
Transfer Coefficients ◽  
Stagnation Region ◽  
Heat Transfer Coefficients ◽  
Impingement Heat Transfer

Stagnation region heat transfer coefficients are obtained from jet impingement onto a concave surface in this experimental investigation. A single row of round jets impinge on the cylindrical target surface to replicate leading edge cooling in a gas turbine airfoil. A modified, transient lumped capacitance experimental technique was developed (and validated) to obtain stagnation region Nusselt numbers with jet-to-target surface temperature differences ranging from 60°F (33.3°C) to 400°F (222.2°C). In addition to varying jet temperatures, the jet Reynolds number (5000–20000), jet-to-jet spacing (s/d = 2–8), jet-to-target surface spacing (ℓ/d = 2–8), and impingement surface diameter-to-jet diameter (D/d = 3.6, 5.5) were independently varied. This parametric investigation has served to develop and validate a new experimental technique which can be used for investigations involving large temperature differences between the surface and fluid. Furthermore, the study has broadened the range of existing correlations currently used to predict heat transfer coefficients for leading edge, jet impingement.

An Experimental Evaluation of Advanced Leading Edge Impingement Cooling Concepts

2000 ◽  
Vol 123 (1) ◽  
pp. 147-153 ◽  
Author(s):  
M. E. Taslim ◽  
L. Setayeshgar ◽  
S. D. Spring
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Transfer Enhancement ◽  
High Surface ◽  
Convective Heat Transfer Coefficient ◽  
Leading Edge ◽  
Target Surface ◽  
Transfer Enhancement

The main objective of this experimental investigation was to measure the convective heat transfer coefficient of impingement for different target wall roughness geometries of an airfoil leading edge, for jet to wall spacings and exit flow schemes. Available data in the open literature apply mostly to impingement on flat or curved smooth surfaces. This investigation covered two relatively new features in blade leading-edge cooling concepts: curved and roughened target surfaces. Experimental results are presented for four test sections representing the leading-edge cooling cavity with cross-over jets impinging on: (1) a smooth wall, (2) a wall with high surface roughness, (3) a wall roughened with conical bumps, and (4) a wall roughened with tapered radial ribs. The tests were run for two supply and three exit flow arrangements and a range of jet Reynolds numbers. The major conclusions of this study were: (a) There is a heat transfer enhancement benefit in roughening the target surface; (b) while the surface roughness increases the impingement heat transfer coefficient, the driving factor in heat transfer enhancement is the increase in surface area; (c) among the four tested surface geometries, the conical bumps produced the highest heat transfer enhancement.

Experimental and Numerical Investigation of Impingement on a Rib-Roughened Leading-Edge Wall

2003 ◽  
Author(s):  
M. E. Taslim ◽  
K. Bakhtari ◽  
H. Liu
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Heat Removal ◽  
Leading Edge ◽  
Target Surface ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Impingement Heat Transfer ◽  
Edge Surface ◽  
Rib Roughened

Effective cooling of the airfoil leading-edge is imperative in gas turbine designs. Amongst several methods of cooling the leading edge, impingement cooling has been utilized in many modern designs. In this method, the cooling air enters the leading edge cavity from the adjacent cavity through a series of crossover holes on the partition wall between the two cavities. The crossover jets impinge on a smooth leading-edge wall and exit through the film holes, and, in some cases, form a crossflow in the leading-edge cavity and move toward the end of the cavity. It was the main objective of this investigation to measure the heat transfer coefficient on a smooth as well as rib-roughened leading-edge wall. Experimental data for impingement on a leading edge surface roughened with different conical bumps and radial ribs are reported by the same authors, previously. This investigation, however, deals with impingement on different horseshoe ribs and makes a comparison between the experimental and numerical results. Three geometries representing the leading-edge cooling cavity of a modern gas turbine airfoil with crossover jets impinging on 1) a smooth wall, 2) a wall roughened with horseshoe ribs, and 3) a wall roughened with notched-horseshoe ribs were investigated. The tests were run for a range of flow arrangements and jet Reynolds numbers. The major conclusions of this study were: a) Impingement on the smooth target surface produced the highest overall heat transfer coefficients followed by the notched-horseshoe and horseshoe geometries. b) There is, however, a heat transfer enhancement benefit in roughening the target surface. Amongst the three target surface geometries, the notched-horseshoe ribs produced the highest heat removal from the target surface which was attributed entirely to the area increase of the target surface. c) CFD could be considered as a viable tool for the prediction of impingement heat transfer coefficients on an airfoil leading-edge wall.

Effect of Nozzle-to-Target Spacing on Fin Effectiveness and Convective Heat Transfer Coefficient for Array Jet Impingement Onto Novel Micro-Roughness Structures

2018 ◽  
Author(s):  
Prashant Singh ◽  
Mingyang Zhang ◽  
Shoaib Ahmed ◽  
Srinath V. Ekkad
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat ◽  
Roughness Element ◽  
Convective Heat Transfer Coefficient ◽  
Heat Removal ◽  
Jet Impingement ◽  
Target Surface ◽  
Target Spacing

With recent advancements in the field of additive manufacturing, the design domain for development of complicated cooling configurations has significantly expanded. The motivation of the present study is to develop high-performance impingement cooling designs catered towards application’s requiring high rates of heat removal, e.g. gas turbine blade leading edge and double-wall cooling, air-cooled electronic devices etc. Jet impingement is a popular cooling technique which results in high convective heat rates. In the present study, jet impingement is combined with strategic roughening of the target surface, such that a combined effect of impingement-based and curved-surface area based enhancement in heat transfer coefficient could be achieved. Traditionally, for surface roughening, cylindrical and cubic elements are used. We have demonstrated, through our steady-state experiments, a novel “concentric” shaped roughness element design which has resulted in about 20–60% higher effectiveness compared to smooth target jet impingement, for jet-to-target spacing of one jet diameter. The cubic shaped roughened target yielded about 20% to 40% enhancement in effectiveness, and the cylindrical shaped roughened target yielded 10% to 30% enhancement. Through the plenum pressure measurements, it was found that the addition of the micro-roughness elements does not result in a discernable increment in pressure losses, compared to the standard impingement on the smooth target surface. Hence, the demonstrated configuration with the highest heat transfer coefficient also resulted in the highest thermal hydraulic performance.

Impingement Heat Transfer Enhancement on a Cylindrical, Leading Edge Model With Varying Jet Temperatures

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Evan L. Martin ◽  
Lesley M. Wright ◽  
Daniel C. Crites
Keyword(s):  
Heat Transfer ◽  
Experimental Technique ◽  
Leading Edge ◽  
Jet Impingement ◽  
Target Surface ◽  
Large Temperature ◽  
Transfer Coefficients ◽  
Stagnation Region ◽  
Heat Transfer Coefficients ◽  
Impingement Heat Transfer

Stagnation region heat transfer coefficients are obtained from jet impingement onto a concave surface in this experimental investigation. A single row of round jets impinge on the cylindrical target surface to replicate leading edge cooling in a gas turbine airfoil. A modified, transient lumped capacitance experimental technique was developed (and validated) to obtain stagnation region Nusselt numbers with jet-to-target surface temperature differences ranging from 60 °F (33.3 °C) to 400 °F (222.2 °C). In addition to varying jet temperatures, the jet Reynolds number (5000–20,000), jet-to-jet spacing (s/d = 2–8), jet-to-target surface spacing (ℓ/d = 2–8), and impingement surface diameter-to-jet diameter (D/d = 3.6, 5.5) were independently varied. This parametric investigation has served to develop and validate a new experimental technique, which can be used for investigations involving large temperature differences between the surface and fluid. Furthermore, the study has broadened the range of existing correlations currently used to predict heat transfer coefficients for leading edge jet impingement.

CFD study of slot jet impingement heat transfer with nanofluids

2015 ◽  
Vol 230 (2) ◽  
pp. 206-220 ◽  
Author(s):  
Rabijit Dutta ◽  
Anupam Dewan ◽  
Balaji Srinivasan
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Base Fluid ◽  
Volume Fraction ◽  
Jet Impingement ◽  
Pumping Power ◽  
Inlet Velocity ◽  
Impingement Heat Transfer

We present a numerical investigation of hydrodynamic and heat transfer behaviors for Al2O3–water nanofluids for laminar and turbulent confined slot jets impingement heat transfer at nanoparticle volume fractions of 3% and 6%. A comparison of the nanofluid with the base fluid has been performed for the same Reynolds number and same jet inlet velocity. A single-phase fluid approach was used to model the nanofluid. Further, the thermo-physical properties of nanofluid were calculated using a recent approach. For the same value of Reynolds number, maximum increase in the average heat transfer coefficient at the impingement plate was found to be approximately 27% and 22% for laminar and turbulent slot impingements, respectively, for 6% volume fraction of nanofluid as compared to that of water. However, the pumping power curve showed a steep increase with the volume fraction with nearly five times increase in the pumping power observed for 6% volume fraction nanofluid. Further, the energy-based performance was assessed with the help of the performance evaluation criterion (PEC). PEC values indicate that nanofluids do not necessarily represent the most efficient coolants for this type of application. Moreover, at the same jet inlet velocity, a reduction in the heat transfer coefficient of 7% and 20% was observed for nanofluid as compared to base fluid for laminar and turbulent flows, respectively.

Sign in / Sign up

Export Citation Format

Share Document