Investigation on heat transfer enhancement and pressure loss of double swirl chambers cooling

By merging two standard swirl chambers,an alternative cooling configuration named double swirl chambers(DSC)has been developed.In the DSC cooling configuration,the main physical phenomena of the swirl flow in swirl chamber and the advantages of swirl flow in heat transfer augmentation are maintained.Additionally,three new physical phenomena can be found in DSC cooling configuration,which result in a further improvement of the heat transfer:(1)impingement effect has been observed,(2)internal heat exchange has been enhanced between fluids in two swirls,and(3)“∞”shape swirl has been generated because of cross effect between two chambers,which improves the mixing of the fluids.Because of all these improvements,the DSC cooling configuration leads to a higher globally-averaged thermal performance parameter(Nu/Nu_(∞)/(f/f0)^(1/3))than standard swirl chamber.In particular,at the inlet region,the augmentation of the heat transfer is nearly 7.5 times larger than the fully developed non-swirl turbulent flow and the circumferentially averaged Nusselt number coefficient is 41%larger than the standard swirl chamber.Within the present work,a further investigation on the DSC cooling configuration has been focused on the influence of geometry parameters e.g.merging ratio of chambers and aspect ratio of inlet duct on the cooling perfomance.The results show a very large influence of these geometry parameters in heat transfer enhancement and pressure drop ratio.Compared with the basic configuration of DSC cooling,the improved configuration with 20%to 23%merging ratio shows the highest globally-averaged themal performance parameter.With the same cross section area in tangential inlet ducts,the DSC cooling channel with larger aspect ratio shows larger heat transfer enhancement and at the same time reduced pressure drop ratio,which results in a better globally-averaged themal performance parameter.

Conjugate calculation of a film-cooled blade for improvement of the leading edge cooling configuration

Great efforts are still put into the design process of advanced film-cooling configurations.In particular,the vanes and blades of turbine front stages have to be cooled extensively for a safe operation.The conjugate calculation technique is used for the three dimensional thermal load prediction of a fim-cooled test blade of a modern gas turbine.Thus,it becomes possible to take into account the interaction of internal flows,external flow,and heat transfer without the prescription of heat transfer ooefficients.The focus of the investigation is laid on the leading edge part of the blade.The numerical model consists of all internal flow passages and cooling hole rows at the leading edge.Furthermore,the radial gap flow is also part of the model.The comparison with thermal pyrometer measurements shows that with respect to regions with high thermal load a qualitatively and quantitatively good agreement of the conjugate results and the measurements can be found.In particular,the region in the vicinity of the mid-span section is exposed to a higher thermal load,which requires further improvement of the cooling arrangement.Altogether the achieved results demonstrate that the conjugate calculation technique is applicable for reasonable prediction of three-dimensional thermal load of complex cooling configurations for blades.