[Paper Review] Numerical Investigation of Effects of Compound Angle and Length to Diameter Ratio on Adiabatic Film Cooling Effectiveness

Vidit Sharma, Ashish Garg|arXiv (Cornell University)|May 3, 2014

Turbomachinery Performance and Optimization3 references22 citations

TL;DR

This study numerically investigates how compound angle and length-to-diameter (L/D) ratio affect adiabatic film cooling effectiveness on turbine blades using RANS simulations with a k-ε turbulence model. Results show that a 45° compound angle combined with L/D = 4 delivers the highest cooling effectiveness, while high L/D ratios with large compound angles increase mixing and reduce performance.

ABSTRACT

A modification has been done in the normal injection hole of 35 degree, by injecting the cold fluid at different angles(compound angle) in lateral direction, providing a significant change in the shape of holes which later we found in our numerical investigation giving good quality of effectiveness in cooling. Different L/D ratios are also studied for each compound angle. The numerical simulation is performed based on Reynolds Averaged Navier-Stokes(RANS) equations with k-epsilon turbulence model by using Fluent(Commercial Software). Adiabatic Film Cooling Effectiveness has been studied for compound angles of (0, 30, 45 and 60 degrees) and L/D ratios of (1, 2, 3 and 4) on a hole of 6mm diameter with blowing ratio 0.5. The findings are obtained from the results, concludes that the trend of laterally averaged adiabatic effectiveness is the function of L/D ratio and compound angle.

Motivation & Objective

• To analyze the influence of compound angle and L/D ratio on film cooling effectiveness in gas turbine blades.
• To identify optimal geometric configurations that maximize lateral coverage and cooling performance.
• To evaluate the trade-off between coolant spreading and mixing losses at varying L/D and compound angles.
• To compare compound-angled holes against standard 35° holes in terms of effectiveness and flow dynamics.
• To provide design guidelines for enhanced film cooling using advanced hole geometries and L/D ratios.

Proposed method

• Numerical simulations were performed using the commercial software ANSYS Fluent based on Reynolds-Averaged Navier-Stokes (RANS) equations.
• The standard k-ε turbulence model was applied to capture the turbulent flow characteristics of the coolant jet and mainstream interaction.
• Adiabatic film cooling effectiveness was calculated using the dimensionless temperature difference formula: η = (T_H - T_W)/(T_H - T_C).
• Simulations were conducted for compound angles of 0°, 30°, 45°, and 60°, and L/D ratios of 1, 2, 3, and 4, with a 6 mm diameter hole.
• Blowing ratio was fixed at 0.5, and the hot stream temperature and velocity were maintained constant across cases.
• Laterally averaged effectiveness (η_avg) was computed to evaluate overall cooling performance across the surface.

Experimental results

Research questions

• RQ1 How does increasing the compound angle affect the lateral spreading and effectiveness of film cooling?
• RQ2 What is the influence of L/D ratio on the distribution and persistence of the coolant film downstream?
• RQ3 How do compound angle and L/D ratio interact to affect mixing between cold and hot streams?
• RQ4 Which combination of compound angle and L/D ratio yields the highest average film cooling effectiveness?
• RQ5 Does a higher L/D ratio always improve cooling performance, especially at high compound angles?

Key findings

• The 45° compound angle with L/D = 4 produced the highest laterally averaged film cooling effectiveness across all tested configurations.
• At L/D = 1, increasing the compound angle from 0° to 60° improved effectiveness due to enhanced lateral spreading and reduced vortex formation.
• For L/D = 2, effectiveness decreased significantly at higher compound angles due to increased coolant spreading and earlier mixing with the mainstream.
• At L/D = 3, the 60° compound angle showed superior performance at short downstream distances (X/D < 5), but performance declined further downstream.
• L/D = 4 showed consistently high effectiveness for all compound angles except 60°, where a sharp drop in performance was observed due to excessive mixing.
• The 30° and 45° compound angles demonstrated stable and high effectiveness across all L/D ratios, with 45° outperforming others in both peak and average effectiveness.