Session: 12-04: Film Cooling Computational Studies (II)

Paper Number: 153525

Effect of Blowing Configurations on Heat Transfer Augmentation With Multihole Sweeping Jet Film Cooling 

The growing expectation from modern gas turbine engines for achieving high thrust, power, and efficiency with lower specific fuel consumption motivates the development of efficient gas turbine cooling techniques. Film cooling is the most influential external cooling method that enables the proper functioning of gas turbine components with improved life expectancy. Recent developments in the field of unsteady jets in film cooling open up the domain of advanced research in gas turbine cooling technology. The use of pulsating and oscillating jets for film cooling has been studied extensively. A sweeping jet employed as a film cooling stream over the suction surface of an HP turbine NGV is a promising notion.

In this study, numerical investigations were performed to study the effects of various coolant- blowing configurations on sweeping jet film cooling. An array of sweeping jets in the reversed hole configuration was placed near the leading edge of the HP turbine NGV. The film cooling performance was assessed by computing the augmentation in heat transfer coefficient and net heat flux reduction. For this purpose, 3D-URANS simulations were carried out using Ansys fluent 2022®.

The mainstream flow was achieved by imposing the favorable pressure gradient of the HP turbine NGV suction surface on a flat plate. The freestream Reynolds number (1 x 10⁶) along with the Cp distribution of VKI LS 89 NGV suction surface were ensured for the engine matching conditions. Three sweeping jets were placed on the suction surface at 3.4% of the chord length away from the leading edge. The pitch distance was kept at 6 times the hole diameter with the assumption of translation periodic boundary condition. Initially, the effect of the blowing ratio was studied by increasing the blowing ratio of all three holes. Then, the effect of jet focusing was investigated by increasing the middle jet's blowing ratio while keeping the neighboring jets' coolant flow rate constant. The freestream temperature was kept at 300 K, and the coolant stream was supplied at 167 K, maintaining a density ratio (DR) of 1.8.

Preliminary results indicated that film cooling effectiveness reduces with the increasing blowing ratio and higher heat transfer augmentation was observed at higher blowing ratios. The interaction of sweeping jets promotes intense mixing and increased heat transfer to the vane surface. When only the blowing ratio of the middle jet was increased (jet focusing), the film cooling effectiveness downstream of the middle jet was reduced. The region of neighboring jets was unaffected; hence the focusing of the middle jet showed no significant effect on the

 

laterally averaged film cooling effectiveness. However, it effectively increases the heat transfer augmentation and a noticeable dip was seen in the net heat flux reduction. The duration of the interaction of the middle jet with the neighboring jets was higher in the cases of jet focusing than in the corresponding cases without focusing. This increased the heat transfer to the vane surface without an increase in the coolant flow rate. This suggests that increasing the interaction between the jets without the added protection of increased coolant flow rate may be detrimental to the film cooling performance.

The coolant stream parameters significantly influence the aerodynamics of turbine passage flow and the thermal performance of film cooling. This paper will comprehensively discuss the sweeping jet interaction phenomenon and its effects on film cooling near the leading edge of an HP turbine NGV.

Presenting Author: Hitesh Sharma Indian Institute of Technology Kharagpur

Presenting Author Biography: Mr. Hitesh Sharma is a PhD research scholar at the Indian Institute of Technology Kharagpur, India.

Authors:

Hitesh Sharma Indian Institute of Technology Kharagpur
K S Pavan Kumar Indian Institute of Technology Kharagpur
Arnab Roy Indian Institute of Technology Kharagpur
Chetan Mistry Indian Institute of Technology Kharagpur