Jet impingement technique is widely used in gas turbine system. In jet impingement, the coolant at high velocity issuing from a nozzle impinges on the heated surface of the blade. It channels collision of fluid jet onto a heated surface. It is used for intense localized cooling of hot turbine blade viz., the leading edge. Jet impingement is also used near a mid-chord of blade whose characteristics are similar to impingement over a flat surface. For heat transfer enhancement multiple jets are involved. Many research articles could be found on multi-jet impingement on a flat surface. The present study discusses novel equilateral staggered jet impingement for uniform cooling of flat surface which traditional methods of jet impingement fail. The equilateral staggered arrangement consists of a circular jet surrounded by four neighbouring chamfered jets at an angle of 45°. Large-eddy simulations and mie-scattering imaging techniques are discussed for heat transfer and flow visualization of equilateral staggered chamfered jet arrangement. The validation of the present study is made with existing experimental data on equilateral staggered jet arrangement of round jets on a flat plate. The results are discussed for free as well as for impingement on a flat surface. An equilateral staggered jet arrangement consisting only of circular jets is considered as the base model for comparison. Data is collected for a range of jet Reynolds number (10,000≤Re≤25,000) and jet-to-plate distance. A large number of eddies formation characterize the flow feature and turbulence quantities of equilateral staggered jet arrangement. The eddies always try to reach the centre of the plate (stagnation point) where the incoming jet breaks these eddies into smaller parts. The Mie-scattering imaging shows how jet interacts and merges as it moves downstream. The flow features basically constitute of jet to jet interaction, jet fountain and upwash flow. It is also noticed that every jet cools its own independent area. However with the inclusion of chamfered jets the region of highest heat transfer shifts away from the jet centerline. This happens because of the change in direction of flow of jet because of chamfering.  The heat transfer results are discussed in terms of Nusselt number. The flat plate is constantly heated at a constant heat flux of 3kW/m^2^. The effect of jet-to-jet spacing is also considered on heat transfer and flow characteristics and it has been found as one of the important factors in deciding the uniformity in heat transfer. Nusselt number variation over the flat surface is calculated to measure the uniformity index of heat transfer.


Heat Transfer and Flow Visualization of Equilaterally Staggered Jet Arrangement on a Flat Surface

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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