Design of Cooling Air Flow and Thermal Analysis for an Afterburner V-Gutter

Abstract

Abstract Modern military aircraft engines are designed for high thrust, low specific fuel consumption, small engine size, and high thrust-to-weight ratio. Afterburner is a thrust augmentation device that is used in all modern military aircraft engines. Afterburners are required for aircrafts to take-off from short runways with heavy payloads and to perform combat manoeuvres. Light up and flame stabilization are the key requirements for any afterburner design. From the literature review, V-gutters are known to be the best flame holding devices based on the blockage, flame spread and combustion stability criteria. For the fifth-generation aero engines, the gas temperature at the entry of the afterburner system is higher than the V-gutter material’s allowable limit. Typical turbine entry gas temperatures are of order of 1850 K and reduces to a value of 1100 K at afterburner inlet which necessitates cooling of the V-gutter structure. Uncooled or bare v-gutters are prone to oxidation and damage due to thermal fatigue. The cooling of v-gutter helps to prevent the oxidation and improve the life. In this work, various cooling design configurations for the given V-gutter have been investigated using jet impingement and film cooling techniques. This study aims to develop a cooling arrangement to reduce the average uncooled V-gutter metal temperature from 950 K to less than 750 K by using the bypass air at 3 bar pressure and 550 K temperature. The corresponding average cooling effectiveness of 0.5 is to be achieved. The design of experiments (DOE) methods used for computational studies like Monte Carlo and Montgomery to validate and analyse the designs are computationally intensive and time consuming. Hence, a parametric approach is used for optimization of cooling flow design to achieve the desired temperatures and cooling effectiveness. Conjugate Heat Transfer (CHT) analysis is performed on four distinct cooling configurations with different cooling hole diameters and their arrangement. The first three cooling configurations 1 to 3 do not meet the design requirement. The metal temperature of the V-gutter for cooling design configuration 4a is in the range of 699 K – 859 K with an average metal temperature of 788 K. The cooling design configuration 4b showed the best cooling performance with the V-gutter metal temperature in the range of 580 K – 840 K and an average temperature of 755 K. The corresponding cooling effectiveness achieved is 0.53 with lowest cooling air mass flow requirement is 0.45% of afterburner inlet flow. Thus, it is concluded that the V-gutter cooling configuration 4b meets the design intend.