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

Paper Number: 153531

Effect of Inflow Turbulence on Heat Transfer Augmentation With Multihole Sweeping Jet Film Cooling 

Gas turbines are an essential component in the power and thrust generation sector and they are exposed to a plethora of conditions that decide the longevity and efficiency of the turbine itself and, ultimately, the larger structure of which the turbine is part. The gas turbine industry continuously pushes its limit of entry stage turbine inlet temperature as we progress in time, in pursuit of increasing the efficiency and power output. This shows the need for technology that caters to these high temperatures, which have the potential to melt the turbine blade. Film cooling is one of these technologies, alongside internal cooling and impingement cooling. There has been a lot of research on this topic where the shaped holes are used to cool the turbine blade, and also their drawbacks. Recently pulsating jets, oscillating jets and their applications are being researched extensively. Studying the cooling of turbine blade suction surfaces with these fluid oscillators in different configurations & parameters is of importance in many aspects for exploring future oscillating-based cooling technologies.

The effectiveness of the film cooling is influenced by geometrical parameters as well as flow parameters. A few of them are inflow turbulence intensity, blowing ratio, density ratio, Reynolds number, the pitch and dimensions of holes, etc. In this study, numerical investigations were performed to study the effect of freestream turbulence intensity on the aerodynamics and heat transfer characteristics of sweeping jet film cooling. An array of sweeping jets in reverse configuration was placed near the leading edge of the HP turbine NGV. This oscillator array has a row-wise arrangement with a pitch of 6 times the hole diameter and translational periodic boundary conditions. ANSYS Fluent 2022® was used to run the 3D Unsteady RANS simulations using the SST k-ω modeling for turbulence. The analysis spans three blowing ratios for all the oscillators, i.e., for M = 0.5, 0.75, 1. In each of these cases, the inflow turbulence intensity of the freestream varied from 0.5%, 5%, and 10%. The freestream Reynolds number was set to 10⁶, along with the surface pressure distribution of VKS LS 89 NGV suction surface for engine matching conditions. Density ratio (D.R.) was fixed at 1.8 with freestream and coolant temperatures at 300 K and 167 K, respectively. 

 

Numerical investigations showed that film cooling effectiveness reduces with increasing freestream turbulence intensity. The increase in freestream turbulence enhances the heat transfer of the vane surface. Along with that the interaction between the sweeping jets promotes the mixing of coolant stream and freestream, hence there is a reduction in coolant retainment capacity. The film cooling effectiveness reduces as the blowing ratio increases. However it is interesting to observe that in the streamwise direction, the effect of turbulence on film cooling effectiveness diminishes owing to the turbulence decay. This indicates that the heat transfer is influenced by inflow turbulence, which impacts the film cooling performance. A detailed understanding of jet interaction with variations of inflow turbulence provides insight into the flow complexities and heat transfer for turbine vane film cooling near the Leading edge of the HP Turbine nozzle vane.

Presenting Author: K S Pavan Kumar Indian Institute of Technology Kharagpur

Presenting Author Biography: Mr. K S Pavan Kumar is an undergraduate student at the Indian Institute of Technology Kharagpur.

Authors:

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