Abstract
The present work investigates the flow topology generated by the angled effusion holes of a compact combustor liner assembly. The combustor geometry is designed in a way that the flow conditions are selected corresponding to a 1 KN thrust for a micro gas turbine engine. The combustor operates based on a lean burn combustion technology in which 70% of the air is admitted through the injector and the remaining is sent to the annulus passage of the liner assembly which aids in cooling the liner walls. The angled effusion holes were designed initially on the basis of existing empirical formulas and further iterated according to the numerical analysis to provide an optimum cooling pattern across the combustor length. Optimization of the cooling hole geometry is critical to achieve the desired film cooling effectiveness. The various parameters with important effect on film cooling effectiveness include positioning of holes, dimension, shape (elliptical, circular, or other), number of holes. A detailed parametric study is conducted on a number of geometrical features related to the liner holes such as hole diameter, shape, angle with respect to liner axis, the position of holes, number of rows of holes, the transverse and axial pitch. The combustor is operating at a maximum pressure of 14 bar with a mass flow rate 0.2206 Kg/s coming from the compressor at a temperature of 595K based on the Brayton cycle analysis done for 1kN thrust. The combustor liner is operated at zero pressure drop focusing the geometry in absence of injector where 4 % pressure drop is considered through annulus passage. The combustor is having 70-30 % mass flow split and a uniform temperature of 900K is taken inside the combustion chamber. The combustor cooling is optimized for the minimum pressure drop across the liner. The study is carried out using numerical analysis on the lean burn liner system designed to optimize wall temperature conditions to have control over temperature of emissions reaching the turbine blades and have better service life as a result.
The circular holes of 1.82 mm diameter inclined at an angle of 18-degree result in the best film cooling effectiveness among all geometries. This is decided basis of the temperature plots, pressure drop through holes, and pressure drop across the entry and exit of holes favorable for optimal film cooling effectiveness.
