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Film Effectiveness Correlations for Cylindrical and Fan-Shaped Holes, Introducing Local Pressure Coefficient
Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology. Linköping University, Center for Medical Image Science and Visualization (CMIV).ORCID iD: 0000-0001-5526-2399
Siemens Industrial Turbomachinery AB. (Siemens Industrial Turbomachinery AB)
Siemens Industrial Turbomachinery AB.
2012 (English)In: ASME Turbo Expo 2012: Turbine Technical Conference and Exposition, Volume 4: Heat Transfer, Parts A and B, Copenhagen, Denmark, June 11–15, 2012, ASME Press, 2012, Vol. 4, 1491-1500 p.Conference paper (Refereed)
Abstract [en]

Most of the proposed correlations for prediction of gas turbinefilm cooling performance in the open literature rely on experimentsconducted on flat plates. These correlations neglectadverse pressure gradient effects present in the flow field for airfoillike configurations. The continuous change in flow characteristicsin the main flow field from leading edge to trailingedge that will affect the film cooling performance is also neglected.In this study correlations are derived from measurementsconducted on a gas turbine vane working at engine likeconditions. This will take into account the effect of hole positionand the local flow situation. Indeed, cooling holes locatedat three (five) different positions with blowing ratio ranges from0.3-2.5 (0.9-6) have been considered along the suction (pressure)sides. The non-dimensional pressure coefficient CP, at the exitlocation of each hole has been introduced as a new variable toderive a single correlation for either suction or pressure sides.Three main variables: downstream distance, blowing ratio, andlocal CP together with the two way interaction between thesevariables are introduced into a commercial statistical analysisprogram, Minitab. Stepwise regression analysis has been performedto highlight factors with greatest influence on the correlationmodel. Appropriateness of the derived model is measuredbased on the adjusted coefficient of determination, R2ad j. Correlationsare derived for eight different configurations: for suctionand pressure sides, cylindrical and fan-shaped holes and in thepresence and absence of showerhead cooling. Despite the complexity of the flow due to high blowing ratio (existence of lift off)and also variation of film cooling performance from one positionto another, the calculated R2adj values indicate a high predictabilityof the proposed correlation model. The suggested correlationmodel can be useful for optimizing the location of one or severalrows of cooling holes around the vane and also one single rowperformance.

Place, publisher, year, edition, pages
ASME Press, 2012. Vol. 4, 1491-1500 p.
Keyword [en]
Film Cooling, Gas Turbine, Film effectiveness, Correlation, Fan-shaped Holes, Cylindrical Holes
National Category
Fluid Mechanics and Acoustics
URN: urn:nbn:se:liu:diva-116987DOI: 10.1115/GT2012-69021ISBN: 978-0-7918-4470-0OAI: diva2:801880
ASME Turbo Expo 2012, June 11–15, Copenhagen, Denmark
Turbo Power Program
Available from: 2015-04-10 Created: 2015-04-10 Last updated: 2016-03-14Bibliographically approved
In thesis
1. On Film Cooling of Turbine Guide Vanes: From Experiments and CFD-Simulations to Correlation Development
Open this publication in new window or tab >>On Film Cooling of Turbine Guide Vanes: From Experiments and CFD-Simulations to Correlation Development
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

To achieve high thermal efficiency in modern gas turbines, the turbine-inlet temperature has to be increased. In response to such requisites and to prevent thermal failure of the components exposed to hot gas streams, the use of different cooling techniques, including film cooling, is essential. Finding an optimum film cooling design has become a challenge as it is influenced by a large number of flow and geometrical parameters. This study is dedicated to some important aspects of film cooling of a turbine guide vane and consists of three parts.

The first part is associated with an experimental investigation of the suction and pressure side cooling by means of a transient IR-Thermography technique under engine representative conditions. It is shown that the overall film cooling performance of the suction side can be improved by adding showerhead cooling if fan-shaped holes are used, while cylindrical holes may not necessarily benefit from a showerhead. According to the findings, investigation of an optimum cooling design for the suction side is not only a function of hole shape, blowing ratio, state of approaching flow, etc., but is also highly dependent on the presence/absence of showerhead cooling as well as the number of cooling rows. In this regard, it is also discussed that the combined effect of the adiabatic film effectiveness (AFE) and the heat transfer coefficient (HTC) should be considered in such study. As for the pressure side cooling, it is found that either the showerhead or a single row of cylindrical cooling holes can enhance the HTC substantially, whereas a combination of the two or using fan-shaped holes indicates considerably lower HTC. An important conclusion is that adding more than one cooling row will not augment the HTC and will even decrease it under certain circumstances.

In the second part, computational fluid dynamics (CFD) investigations have shown that film cooling holes subjected to higher flow acceleration will maintain a higher level of AFE. Although this was found to be valid for both suction and pressure side, due to an overall lower acceleration for the pressure side, a lower AFE was achieved. Moreover, the CFD results indicate that fan-shaped holes with low area ratio (dictated by design constraints for medium-size gas turbines), suffer from cooling jet separation and hence reduction in AFE for blowing ratios above unity. Verification of these conclusions by experiments suggests that CFD can be used more extensively, e.g. for parametric studies.

The last part deals with method development for deriving correlations based on experimental data to support engineers in the design stage. The proposed method and the ultimate correlation model could successfully correlate the laterally averaged AFE to the downstream distance, the blowing ratio and the local pressure coefficient representing the effect of approaching flow. The applicability of the method has been examined and the high level of predictability of the final model demonstrates its suitability to be used for design purposes in the future.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2015. 68 p.
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1643
Film Cooling, Gas Turbine, Correlation, CFD, Cylindrical holes, Fan-shaped Holes
National Category
Fluid Mechanics and Acoustics
urn:nbn:se:liu:diva-117029 (URN)10.3384/diss.diva-117029 (DOI)978-91-7519-125-6 (print) (ISBN)
Public defence
2015-06-05, ACAS, A huset, Campus Valla, Linkoping, 10:15 (English)
Turbo Power Program
Available from: 2015-04-16 Created: 2015-04-11 Last updated: 2016-03-14Bibliographically approved

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Nadali Najafabadi, HosseinKarlsson, Matts
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