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On Film Cooling of Turbine Guide Vanes: From Experiments and CFD-Simulations to Correlation Development
Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
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.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1643
Keyword [en]
Film Cooling, Gas Turbine, Correlation, CFD, Cylindrical holes, Fan-shaped Holes
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:liu:diva-117029DOI: 10.3384/diss.diva-117029ISBN: 978-91-7519-125-6 (print)OAI: oai:DiVA.org:liu-117029DiVA: diva2:802172
Public defence
2015-06-05, ACAS, A huset, Campus Valla, Linkoping, 10:15 (English)
Opponent
Supervisors
Projects
Turbo Power Program
Available from: 2015-04-16 Created: 2015-04-11 Last updated: 2016-03-14Bibliographically approved
List of papers
1. Film Cooling Performance of a Turbine Vane Suction Side: The Showerhead Effect on Film Cooling Hole Placement for Cylindrical and Fan-Shaped Holes
Open this publication in new window or tab >>Film Cooling Performance of a Turbine Vane Suction Side: The Showerhead Effect on Film Cooling Hole Placement for Cylindrical and Fan-Shaped Holes
2015 (English)In: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 137, no 9, 091005Article in journal (Refereed) Published
Abstract [en]

In this paper, the transient IR-thermography method is used to investigate the effect of showerhead cooling on the film-cooling performance of the suction side of a turbine guide vane working under engine-representative conditions. The resulting adiabatic film effectiveness, heat transfer coefficient (HTC) augmentation, and net heat flux reduction (NHFR) due to insertion of rows of cooling holes at two different locations in the presence and absence of the showerhead cooling are presented. One row of cooling holes is located in the relatively high convex surface curvature region, while the other is situated closer to the maximum throat velocity. In the latter case, a double staggered row of fan-shaped cooling holes has been considered for cross-comparison with the single row at the same position. Both cylindrical and fan-shaped holes have been examined, where the characteristics of fan-shaped holes are based on design constraints for medium size gas turbines. The blowing rates tested are 0.6, 0.9, and 1.2 for single and double cooling rows, whereas the showerhead blowing is maintained at constant nominal blowing rate. The adiabatic film effectiveness results indicate that most noticable effects from the showerhead can be seen for the cooling row located on the higher convex surface curvature. This observation holds for both cylindrical and fan-shaped holes. These findings suggest that while the showerhead blowing does not have much impact on this cooling row from HTC enhancement perspective, it is influential in determination of the HTC augmentation for the cooling row close to the maximum throat velocity. The double-row fan-shaped cooling seems to be less affected by an upstream showerhead blowing when considering HTC enhancement, but it makes a major contribution in defining adiabatic film effectiveness. The NHFR results highlight the fact that cylindrical holes are not significantly affected by the showerhead cooling regardless of their position, but showerhead blowing can play an important role in determining the overall film-cooling performance of fan-shaped holes (for both the cooling row located on the higher convex surface curvature and the cooling row close to the maximum throat velocity), for both the single and the double row cases.

Place, publisher, year, edition, pages
ASME Press, 2015
Keyword
Film cooling, Showerhead cooling, Cylindrical holes, Fan-shaped holes, Gas Turbine
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:liu:diva-116936 (URN)10.1115/1.4029966 (DOI)000377794200005 ()
Projects
Turbo Power Program
Note

Funding agencies: Swedish Energy Agency; Siemens Industrial Turbomachinery AB; GKN Aerospace Sweden AB; Royal Institute of Technology through the Swedish research program TURBO POWER

Available from: 2015-04-10 Created: 2015-04-10 Last updated: 2017-12-04Bibliographically approved
2. Film Cooling Performance of Multiple Arrays of Cylindrical and Fan-Shaped Holes
Open this publication in new window or tab >>Film Cooling Performance of Multiple Arrays of Cylindrical and Fan-Shaped Holes
Show others...
2015 (English)In: Journal of Propulsion and Power, ISSN 0748-4658, E-ISSN 1533-3876, Vol. 31, no 6, 1621-1630 p.Article in journal (Refereed) Published
Abstract [en]

Experimental investigations are performed on the suction side of a cooled turbineguide vane. Transient IR thermography is used to evaluate film cooling performanceof cylindrical and fan-shaped holes in a test facility representing engine conditions.Adiabatic film effectiveness (AFE) and net heat flux reduction (NHFR) results due tocoolant injection through double and multiple rows in the presence and absence of anupstream showerhead are presented. Two double staggered rows at different positionshave been cross-compared; one at a relatively high convex curvature region and theother close to the maximum throat velocity. A combination of the two double rowsis considered to be multiple rows. The tested blowing ratios are in the interval of[0.6 – 1.2] and [0.3 – 1.2] for double and multiple rows, respectively. The showerheadcooling is maintained at nominal blowing ratio. The findings suggest that the choice ofbest cooling hole shape for film cooling design can be highly influenced by the numberof cooling rows to be used and also the presence (or absence) of showerhead cooling.It is worth noting that the outcome may differ depending on the quantity of interest, i.e. AFE or NHFR.

Place, publisher, year, edition, pages
American Institute of Aeronautics and Astronautics, 2015
Keyword
Film Cooling, Gas Turbine, Film Effectiveness, Net Heat Flux Reduction, Cylindrical Holes, Fan-shaped Holes
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:liu:diva-117030 (URN)10.2514/1.B35618 (DOI)000368248000011 ()
Projects
Turbo Power Program
Note

Funding agencies: Swedish Energy Agency; Siemens Industrial Turbomachinery, AB; GKN Aerospace Sweden, AB; Royal Institute of Technology through the Swedish research program TURBO POWER

Vid tiden för disputationen förelåg publikationen endast som manuskript

Available from: 2015-04-11 Created: 2015-04-11 Last updated: 2017-12-04Bibliographically approved
3. Film Cooling Jet Injection Effect in Heat Transfer Coefficient Augmentation for the Pressure Side Cooling of Turbine Vane
Open this publication in new window or tab >>Film Cooling Jet Injection Effect in Heat Transfer Coefficient Augmentation for the Pressure Side Cooling of Turbine Vane
2014 (English)In: ASME Turbo Expo 2014: Turbine Technical Conference and Exposition, American Society of Mechanical Engineers , 2014, Vol. 5B, Paper No. GT2014-26055- p.Conference paper, Published paper (Refereed)
Abstract [en]

Improving film cooling performance of turbine vanes and blades is often achieved through application of multiple arrays of cooling holes on the suction side, the showerhead region and the pressure side. This study investigates the pressure side cooling under the influence of single and multiple rows of cooling in the presence of a showerhead from a heat transfer coefficient augmentation perspective. Experiments are conducted on a prototype turbine vane working at engine representative conditions. Transient IR thermography is used to measure time-resolved surface temperature and the semi-infinite method is utilized to calculate the heat transfer coefficient on a low conductive material. Investigations are performed for cylindrical and fan-shaped holes covering blowing ratio 0.6 and 1.8 at density ratio of about unity. The freestream turbulence is approximately 5% close to the leading edge.

The resulting heat transfer coefficient enhancement, the ratio of HTC with to that without film cooling, from different case scenarios have been compared to showerhead cooling only. Findings of the study highlight the importance of showerhead cooling to be used with additional row of cooling on the pressure side in order to reduce heat transfer coefficient enhancement. In addition, it is shown that extra rows of cooling will not significantly influence heat transfer augmentation, regardless of the cooling hole shape.

Place, publisher, year, edition, pages
American Society of Mechanical Engineers, 2014
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:liu:diva-111022 (URN)10.1115/GT2014-26055 (DOI)000362139100038 ()978-0-7918-4572-1 (ISBN)
Conference
ASME Turbo Expo 2014: Turbine Technical Conference and Exposition, Düsseldorf, Germany, June 16–20, 2014
Available from: 2014-10-03 Created: 2014-10-03 Last updated: 2016-03-14Bibliographically approved
4. CFD Based Sensitivity Analysis of Influencing Flow Parameters for Cylindrical and Shaped Holes in a Gas Turbine Vane
Open this publication in new window or tab >>CFD Based Sensitivity Analysis of Influencing Flow Parameters for Cylindrical and Shaped Holes in a Gas Turbine Vane
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, 1501-1509 p.Conference paper, Published paper (Refereed)
Abstract [en]

In this study a CFD based sensitivity analysis is performedincluding the flow parameter blowing ratio, the geometrical parametercooling hole shape and the effect of approaching flow(hole position), investigating the film cooling performance of areal vane configuration working at engine like conditions. Forthis purpose numerical results from the commercial CFD codeFLUENT using the Spalart-Allmaras turbulence model has beenvalidated versus experimental results on the same vane includingthe film cooling hole configurations. Blowing ratios ranging from(0.2-1.8) have been considered. In addition, film cooling performanceof rows of cooling holes at six different positions locatedaround the suction and pressure side of the vane are investigatedfor studying the influence of flow acceleration present in turbinevanes. These flow parameters are investigated for both cylindricaland fan-shaped holes. Investigations are performed at afixed unity density ratio. It has been found that for fan-shapedholes film cooling performance is higher for cooling holes locatedat positions whit a high accelerated flow. On the otherhand, film cooling performance of cylindrical holes are found tobe affected less by acceleration. Due to the low velocity and lowacceleration on the pressure side the hole position seems to haverelatively low influence on the cooling performance.

Place, publisher, year, edition, pages
ASME Press, 2012
Keyword
Computational Fluid Dynamics, Film Cooling, Fan-shaped Holes, Cylindrical Holes
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:liu:diva-116938 (URN)10.1115/GT2012-69023 (DOI)978-0-7918-4470-0 (ISBN)
Conference
ASME Turbo Expo 2012, June 11-12, Copenhagen, Denmark
Projects
Turbo Power Program
Available from: 2015-04-10 Created: 2015-04-10 Last updated: 2016-03-14Bibliographically approved
5. Film Effectiveness Correlations for Cylindrical and Fan-Shaped Holes, Introducing Local Pressure Coefficient
Open this publication in new window or tab >>Film Effectiveness Correlations for Cylindrical and Fan-Shaped Holes, Introducing Local Pressure Coefficient
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, Published 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
Keyword
Film Cooling, Gas Turbine, Film effectiveness, Correlation, Fan-shaped Holes, Cylindrical Holes
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:liu:diva-116987 (URN)10.1115/GT2012-69021 (DOI)000335868900132 ()978-0-7918-4470-0 (ISBN)
Conference
ASME Turbo Expo 2012, June 11–15, Copenhagen, Denmark
Projects
Turbo Power Program
Available from: 2015-04-10 Created: 2015-04-10 Last updated: 2017-03-07Bibliographically approved

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Nadali Najafabadi, Hossein

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