Metering Characteristics of the Openings Used for the Cooling Systems of Gas Turbines

Abstract

Consideration was given to the known methods that are widely used for computation of the metering characteristics of the openings designed for gas turbine cooling systems. The methods are based on the use of such notions as the flow coefficient and the hydraulic resistance coefficient. The use of the latter is preferable for the design of cooling systems, because it correlates the air rate with the total pressure drop in the channels. To use the flow coefficient for the general cooling system computation algorithm the relation between it and the hydraulic resistance coefficient was established. Due to the fact that the extensive experimental data on the hydraulic resistance of openings are related to noncondensable media the method was developed that enables their use taking into account the compressibility. The method consists in the division of overall losses of the total pressure in the diaphragm into the elements, in particular opening inlet pressure losses, opening outlet pressure losses and friction pressure losses. The air density and the Mach number were defined for each element. The relationship was proposed to take into account the influence the setting angles of openings have on the hydraulic resistance. The method used for computation of the metering characteristics of openings showed a sufficiently good coincidence with experimental data when the pressure ratio values varied in the range of P 1 * /P 2 = 1 to 2.5, a relative length of the channel was in the range of l/d = 6.4 to 24.3 and setting angles of the opening were 30°, 45°, 90°. The data given in the paper are of great practical interest, because the gas turbine cooling system behavior is defined to a great extent by pressure losses in the multiple openings.