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- Kinell, Mats, et al.
(författare)
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Fan Shaped And Cylindrical Holes Studied in a Vane Film Cooling Test Rig
- 2010
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Ingår i: Proceedings of the Asme Turbo Expo 2010, Vol 4, Pts a and B. - 9780791843994 - 9780791838723 ; , s. 1777-1784
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Konferensbidrag (refereegranskat)abstract
- In order to optimize the vane film cooling and thereby increase the efficiency of a gas turbine, different film cooling configurations were experimentally investigated. Dynamic similarity was obtained regarding main flow Reynolds number, airfoil pressure coefficient, adiabatic wall temperature and film cooling ejection ratio. The maximum reached Mach number was 0.52. The geometry of the test section, consisting of one vane and two flow paths, was modified in order to meet the dimensionless pressure coefficient distribution around the airfoil experienced by a full stage airfoil. This would ascertain that scaled but engine realistic pressure gradients would be achieved in the rig test.During the test, the cold airfoil was suddenly imposed to a hot main stream and the evaluation of both the film cooling effectiveness and the heat transfer coefficient distribution on the visiable surface could be done at one single test using timeresolved temperature measurements obtained through IR thermography. A high resolution MWIR camera was used together with a silicon viewing window. The post-processing allowed for corrections regarding emissions and determination of the desired parameters on the vane surface.Results, heat transfer coefficients and film cooling effectiveness, for fan shaped and cylindrical film cooling holes configurations are compared. The results show clear benefit of using shaped holes over cylindrical ditto, especially on the suction side where near hole film effectiveness is enhanced by approximately 25%, but the results also show that this benefit diminishes to nothing in the suction side trailing edge region.The local heat transfer coefficients are generally lower for the shaped hole configurations. Contrary to the film effectiveness the shaped holes configurations show lower heat transfer coefficients also at the suction side trailing edge region, making use of the shaped hole configurations superior to cylindrical ones as the heat flux to the surface is reduced.Numerical predictions using a boundary layer code, TEXSTAN, and CFD, for a smooth wall configuration corresponds well with the measured results.
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- Salameh, Tareq, et al.
(författare)
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An Experimental Study of Heat Transfer and Pressure Drop on the Bend Surface of a U-duct
- 2010
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Ingår i: Proceedings Of The Asme Turbo Expo 2010, Vol 4, Pts A And B. - 9780791843994 ; 4, s. 13-21
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Konferensbidrag (refereegranskat)abstract
- This work concerns an experimental study of pressure drop and heat transfer for turbulent flow inside a U-duct. Such duct geometries can be found in many engineering applications where cooling air extracts heat from hot internal walls of the duct, e.g., passage cooling inside gas turbine blades. Both friction factors and convective heat transfer coefficients were measured inside a U-duct for three different cases, namely (a) the smooth straight part, (b) the smooth bend (turn) part, and (c) a rough (ribbed) bend (turn) part. The details of the duct geometry were as follows: the cross section area of the straight part was 50x50 mm(2), the inside length of the bend part 240 mm, the cross section area of the rib was 5x5 mm(2) and the rib height-to-hydraulic diameter ratio, e/D-h, was 0.1. The Reynolds number was varied from 8,000 to 20,000. The test rig has been built in such a way that various experimental setups can be handled as the bend (turn) part of the U-duct can easily be removed and the rib configuration can be changed. Both the U-duct and the rib were made from plexiglass material to allow optical access for measuring the surface temperature by using a high-resolution measurement technique based on narrow band thermochromic liquid crystals (TLC R35C5W) and a CCD camera placed facing the bend (turn) part of the U-duct. The calibration of the TLC is based on the hue-based color decomposition system using an in-house designed calibration box. The rib was placed transversely to the direction of the main flow at the outer wall of the bend (turn) part where the wall was heated by an electrical heater. The friction factor ratio and the heat transfer enhancement ratio for case (c) at a Reynolds number of 20,000 were 48.75 and 2.66, respectively. It is found that the presence of the rib increases the heat transfer coefficient on the outer wall of the bend part (tip of side U-duct). The uncertainties were 3% and 6% for the Nusselt number and friction factor, respectively.
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| 4. |
- Xie, Gongnan, et al.
(författare)
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Predictions of Enhanced Heat Transfer of an Internal Blade Tip-Wall with Hemishperical Dimples or Protrusions
- 2010
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Ingår i: Proceedings of the Asme Turbo Expo 2010, Volume 4: Heat Transfer, Parts A and B. - 9780791843994 ; , s. 91-100
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Konferensbidrag (refereegranskat)abstract
- The blade tip region encounters high thermal loads because of the hot gas leakage flows, and it must therefore be cooled to ensure a long durability and safe operation. A common way to cool a blade tip is to design serpentine passages with 180-deg turn under the blade tip-cap inside the turbine blade. Improved internal convective cooling is therefore required to increase the blade tip lifetime. Dimples and protrusions are well recognized as effective devices to augment heat transfer in various applications. In this paper, enhanced heat transfer of an internal blade tip-wall has been predicted numerically. The computational models consist of a two-pass channel with 180-deg turn and arrays of hemispherical dimples or protrusions internally mounted on the tip-wall. Inlet Reynolds numbers are in the range of 100,000 to 600,000. The computations are three dimensional, steady, incompressible and non-rotating. The overall performance of the two-pass channels is also evaluated. It is found that due to the combination of turning impingement and protrusion crossflow or dimple advection, the heat transfer coefficient of the augmented tip is a factor of 2.0 higher than that of a smooth tip. This augmentation is achieved at the cost of a penalty of pressure drop by around 5%. By comparing the present dimples or protrusions performance with others in previous works, it is found that the augmented-tips show the best performance, and the dimpled or protruded tips are superior to those pin-finned tips when the active area enhancement is excluded. It is suggested that dimples and protrusions can be used to enhance blade tip heat transfer and hence improve blade tip cooling.
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