Effects of alternating elliptical chamber on jet impingement heat transfer in vane leading edge under different cross-flow conditions

2021 ◽  
pp. 1-17
Author(s):  
K. Xiao ◽  
J. He ◽  
Z. Feng
Keyword(s):  
Heat Transfer ◽  
Velocity Ratio ◽  
Cross Flow ◽  
Leading Edge ◽  
Longitudinal Vortices ◽  
Impingement Jet ◽  
Flow And Heat Transfer ◽  
Impingement Heat Transfer ◽  
Cross Flow Velocity ◽  
The Cross

ABSTRACT This paper proposes an alternating elliptical impingement chamber in the leading edge of a gas turbine to restrain the cross flow and enhance the heat transfer, and investigates the detailed flow and heat transfer characteristics. The chamber consists of straight sections and transition sections. Numerical simulations are performed by solving the three-dimensional (3D) steady Reynolds-Averaged Navier–Stokes (RANS) equations with the Shear Stress Transport (SST) k– $\omega$ turbulence model. The influences of alternating the cross section on the impingement flow and heat transfer of the chamber are studied by comparison with a smooth semi-elliptical impingement chamber at a cross-flow Velocity Ratio (VR) of 0.2 and Temperature Ratio (TR) of 1.00 in the primary study. Then, the effects of the cross-flow VR and TR are further investigated. The results reveal that, in the semi-elliptical impingement chamber, the impingement jet is deflected by the cross flow and the heat transfer performance is degraded. However, in the alternating elliptical chamber, the cross flow is transformed to a pair of longitudinal vortices, and the flow direction at the centre of the cross section is parallel to the impingement jet, thus improving the jet penetration ability and enhancing the impingement heat transfer. In addition, the heat transfer in the semi-elliptical chamber degrades rapidly away from the stagnation region, while the longitudinal vortices enhance the heat transfer further, making the heat transfer coefficient distribution more uniform. The Nusselt number decreases with increase of VR and TR for both the semi-elliptical chamber and the alternating elliptical chamber. The alternating elliptical chamber enhances the heat transfer and moves the stagnation point up for all VR and TR, and the heat transfer enhancement is more obvious at high cross-flow velocity ratio.

Experimental Investigation of Jet Impingement Heat Transfer in Cross-Flow Modified by a V-Shaped Rib

2014 ◽  
Author(s):  
Chenglong Wang ◽  
Lei Wang ◽  
Bengt Sundén
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Velocity Ratio ◽  
Cross Flow ◽  
Jet Impingement ◽  
Impinging Jet ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Impingement Heat Transfer ◽  
The Cross

Experimental studies are carried out to investigate the jet impingement heat transfer characteristics in cross-flow with and without the presence of a 45 deg V-shaped rib. The local heat transfer coefficients are obtained by a liquid crystal thermography (LCT) technique. The ratio of nozzle-to-surface spacing to jet diameter is 3.56, the jet Reynolds number is kept at 17,000, the cross-flow Reynolds number spans from 32,700 to 65,000, the velocity ratio of jet to cross-flow ranges from 1.5 to 3.0. The impingement heat transfer characteristics in cross-flow are changed from the results without the cross-flow, and they are strongly affected by the velocity ratio. The presence of a V-shaped rib significantly modifies the heat transfer patterns of the impinging jet in cross-flow. Compared to the results without ribs, the heat transfer over the ribbed surface is enhanced for a low velocity ratio but retarded for a high velocity ratio, depending on the interaction between the rib induced flow and the impinging jet.

scholarly journals Enhancement of Impingement Heat Transfer With the Crossflow Normal to Ribs and Pins Between Each Row of Holes

2018 ◽  
Author(s):  
Abubakar M. El-Jummah ◽  
Gordon E. Andrews ◽  
John E. J. Staggs
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Pressure Loss ◽  
Cross Flow ◽  
Experimental Results ◽  
Hole Density ◽  
Impingement Heat Transfer ◽  
The Cross ◽  
Flow Maldistribution

Impingement heat transfer investigations with obstacle (fins) on the target surface were carried out with the obstacles aligned normal to the cross-flow. Conjugate heat transfer (CHT) computational fluid dynamics (CFD) analysis were used for the geometries previously been investigated experimentally. A 10 × 10 row of impingement jet holes or hole density, n, of 4306 m−2 with ten rows of holes in the cross-flow direction was used. The impingement hole pitch X to diameter D, X/D, and gap Z to diameter, Z/D, ratios were kept constant at 4.66 and 3.06 for X, D and Z of 15.24, 3.27 and 10.00 mm, respectively. Nimonic 75 test walls were used with a thickness of 6.35 mm. Two different shaped obstacles of the same flow blockage were investigated: a continuous rectangular ribbed wall of 4.5 mm height, H, and 3.0 mm thick and 8 mm high rectangular pin-fins that were 8.6 mm wide and 3.0 mm thick. The obstacles were equally spaced on the centre-line between each row of impingement jets and aligned normal to the cross-flow. The two obstacles had height to diameter ratios, H/D, of 1.38 and 2.45, respectively. Comparison of the predictions and experimental results were made for the flow pressure loss, ΔP/P, and the surface average heat transfer coefficient (HTC), h. The computations were carried out for air coolant mass flux, G, of 1.08, 1.48 and 1.94 kg/sm2bar. The pressure loss and surface average HTC for all the predicted G showed reasonable agreement with the experimental results, but the predictions for surface averaged h were below the measured values by 5–10%. The predictions showed that the main effect of the ribs and pins was to increase the pressure loss, which led to an increased flow maldistribution between the ten rows of holes. This led to lower heat transfer over the first 5 holes and higher heat transfer over the last 3 holes and the net result was little benefit of either obstacle relative to a smooth wall. The results were significantly worse than the same obstacles aligned for co-flow, where the flow maldistribution changes were lower and there was a net benefit of the obstacles on the surface averaged heat transfer coefficient.

Experimental and Numerical Impingement Heat Transfer in an Airfoil Leading-Edge Cooling Channel With Cross-Flow

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
M. E. Taslim ◽  
D. Bethka
Keyword(s):  
Heat Transfer ◽  
Mass Flow ◽  
Convective Heat Transfer Coefficient ◽  
Cross Flow ◽  
Internal Heat ◽  
Leading Edge ◽  
Impinging Jet ◽  
Experimental Results ◽  
Transfer Coefficients ◽  
Impingement Heat Transfer

To enhance the internal heat transfer around the airfoil leading-edge area, a combination of rib-roughened cooling channels, film cooling, and impingement cooling is often employed. Experimental data for impingement on various leading-edge geometries are reported by these and other investigators. The effects of strong cross-flows on the leading—edge impingement heat transfer, however, have not been studied to that extent. This investigation dealt with impingement on the leading edge of an airfoil in the presence of cross-flows beyond the cross-flow created by the upstream jets (spent air). Measurements of heat transfer coefficients on the airfoil nose area as well as the pressure and suction side areas are reported. The tests were run for a range of axial to jet mass flow rates (Maxial∕Mjet) ranging from 1.14 to 6.4 and jet Reynolds numbers ranging from 8000 to 48,000. Comparisons are also made between the experimental results of impingement with and without the presence of cross-flow and between representative numerical and measured heat transfer results. It was concluded that (a) the presence of the external cross-flow reduces the impinging jet effectiveness both on the nose and sidewalls; (b) even for an axial to jet mass flow ratio as high as 5, the convective heat transfer coefficient produced by the axial channel flow was less than that of the impinging jet without the presence of the external cross-flow; and (c) the agreement between the numerical and experimental results was reasonable with an average difference ranging from −8% to −20%.

scholarly journals Conjugate Heat Transfer CFD Predictions of Impingement Jet Array Flat Wall Cooling Aerodynamics With Single Sided Flow Exit

2013 ◽  
Author(s):  
Abubakar M. El-Jummah ◽  
Gordon E. Andrews ◽  
John E. J. Staggs
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Conjugate Heat Transfer ◽  
Cross Flow ◽  
Diameter Ratio ◽  
Significant Feature ◽  
Axial Distance ◽  
Impingement Jet ◽  
The Cross

Conjugate heat transfer CFD studies were undertaken on impingement square jet arrays with self induced crossflow in the impingement gap with a single sided exit. The aim was to understand the aerodynamic interactions that result in the deterioration of heat transfer with axial distance, whereas the addition of duct flow heat transfer would be expected to lead to an increase in heat transfer with axial distance. A square array of impingement holes was investigated for a common geometry investigated experimentally, pitch to diameter ratio X/D of 5 and impingement gap to diameter ratio Z/D of 3.3 for 11 rows of holes in the crossflow direction. A metal duct wall was used as the impingement surface with an applied heat flux of 100kW/m2, which for a gas turbine combustor cooling application operating at steady state with a temperature difference of ∼450K corresponds to a convective heat transfer coefficient of ∼200 W/m2K. A key feature of the predicted aerodynamics was recirculation in the plane of the impingement jets normal to the cross-flow, which produced heating of the impingement jet wall. This reverse flow jet was deflected by the cross flow which had its peak velocity in the plane between the high velocity impingement jets. The cross-flow interaction with the impingement jets reduced the interaction between the jets on the surface, with lower surface turbulence as a result and this reduced the surface convective heat transfer. A significant feature of the predictions was the interaction of the cross-flow aerodynamics with the impingement jet wall and associated heat transfer to that wall. The results showed that the deterioration in heat transfer with axial distance was well predicted, together with predictions of the impingement wall surface temperature gradients.

Combination of Impingement and Trip Strips for Combustor Liner Backside Cooling

Volume 3 ◽  
2004 ◽  
Author(s):  
Ryan Hebert ◽  
Srinath V. Ekkad ◽  
Vivek Khanna
Keyword(s):  
Heat Transfer ◽  
Cross Flow ◽  
Jet Impingement ◽  
Reynolds Numbers ◽  
Combination Technique ◽  
Impingement Jet ◽  
Impingement Heat Transfer ◽  
Flow Effects ◽  
Heat Transfer Degradation ◽  
Cooling Air

Effective cooling of modern low NOx combustor liners is achieved through combinations of impingement and other heat transfer enhancement methods. In the present study, a combination of impingement and trip strips is studied to determine the optimum location of trip strips with respect to impingement jet arrays. Heat transfer with pure impingement has degradation downstream due to increased cross-flow effects. To counter the cross-flow induced heat transfer degradation, a combination technique wherein impingement is combined with ribs placed in between impingement rows or downstream of the impingement array is studied. Three configurations with increased rib placements and reduced impingement holes are studied and compared with pure impingement cases for the same jet Reynolds number. Three jet Reynolds numbers are studied for Rej = 10000, 20000, and 30000. Detailed heat transfer distributions are obtained using the transient liquid crystal technique. Results show that the presence of ribs increases jet impingement heat transfer on the surface with lower mass flows. The effectiveness of the combination ribs and impingement can provide higher heat transfer with reduced cooling air requirements.

Effect of Artificial Perturbation on Unsteady Wake Vortices in Jets in Cross-Flow

2012 ◽  
Author(s):  
Ivana Milanovic ◽  
Khairul B. M. Q. Zaman ◽  
Timothy J. Bencic
Keyword(s):  
Free Stream ◽  
Velocity Ratio ◽  
Cross Flow ◽  
Wake Vortices ◽  
Smoke Flow ◽  
Unsteady Wake ◽  
Cross Flow Velocity ◽  
Flow Visualizations ◽  
The Cross ◽  
Ratio Range

The current experimental study investigated unsteady wake vortices of jets in cross-flow in order to explore the possibility of periodic perturbation of these vortices with the method of oscillating tabs. Two triangular tabs were placed at the 90° and 270° edges of the jet orifice relative to the direction of the cross-flow. An isolated circular jet passed through a nozzle and entered the cross-flow normal to the wall. Free stream velocities up to 4.1 m/s and jet-to-cross-flow velocity ratio range between 3 and 12 were covered. Strouhal number (fpD/Ucf) for excitation cases was about 0.19. The oscillation frequency was somewhat higher than the ‘preferred’ frequency of the wake vortices. The smoke flow visualizations did not indicate an organization of wake vortices. Artificial excitation simply tilted the jet cross section from side to side in sync with the tab oscillation.

scholarly journals Predictions of Impingement Heat Transfer With Dimples, Pin-Fins and Zig-Zag Rib Obstacles: Conjugate Heat Transfer Computational Fluid Dynamics Predictions

2019 ◽  
Author(s):  
Abubakar M. El-Jummah ◽  
Gordon E. Andrews ◽  
John E. J. Staggs
Keyword(s):  
Heat Transfer ◽  
Pressure Loss ◽  
Cross Flow ◽  
Target Surface ◽  
Smooth Wall ◽  
Transfer Enhancement ◽  
Air Mass ◽  
Impingement Jet ◽  
Impingement Heat Transfer ◽  
Pin Fins

Abstract Regenerative cooling of low NOx gas turbine combustors was investigated using impingement heat transfer with all the combustion air used for wall cooling prior to passing to the flame stabiliser. 10 rows of impingement holes were modelled. Three obstacles were compared with smooth wall impingement heat transfer. The CHT/CFD methodology used was that validated against experimental results in previous publications of the authors. The impingement heat transfer enhancement geometries investigated were circular pin-fins, dimples and zig-zag ribs, which were aligned transverse to the direction of the cross-flow on the impingement target surface. The obstacles were equally spaced on the centre-line between each row of impingement jets transverse to the cross-flow. One heat transfer enhancement obstacle was used per impingement jet air hole. The CFD calculations were carried out for an air mass flux G of 1.08, 1.48 and 1.94 kg/sm2bara, which are the high flow rates used for regenerative combustor wall cooling. Comparison of the current CFD predictions and previous CFD work, that have experimental data, were made for the flow pressure loss and the surface and locally X2 average HTC, h. It was concluded that none of the obstacles in the impingement gap a significant increase in the surface averaged heat transfer coefficient (HTC). The impact of the obstacles was to increase the flow maldistribution due to the increased pressure loss. This resulted is less heat transfer from the reduced air mass flow in the first 4 holes and increased heat transfer in the last 4 holes, relative to the smooth wall results. The main effect of the obstacles was to increase the heat transfer to the impingement jet surface. The dimpled surface was predicted to have a very poor performance, with significantly reduced impingement heat transfer. This was due to the impingement jets being deflected away from the target surface by the shape of the dimples and this reduced the surface heat transfer.

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