Heat Transfer and Pressure Drop Characteristics for a Turbine Casing Impingement Cooling System

Abstract

Flow mechanisms, heat transfer and discharge coefficient characteristics for a representative part of a turbine casing cooling system, consisting of an array of 20 impinging jets, were numerically investigated. The study focused on the influence of the jet Mach number while maintaining the Reynolds number constant at Re = 7,500. Therefore, the orifice bore diameter or the fluid density had to be varied. The objectives of the current CFD simulations have not been adressed before in literature, not only because heat transfer characteristics and pressure drop are given for impingement jet Mach numbers up to 0.72 at a constant relatively low Reynolds number, but also because fundamental understanding of physical phenomena of the flow in the cylindrical plenum and in the small sharp-edged orifices at the bottom side of the tube is provided. Increasing the Mach number by simultaneously reducing the orifice diameters led to slightly decreasing Nusselt numbers, with average deviations of the order of 14%. However, the heat transfer coefficient increased considerably with increasing Mach number. On the contrary, the variation of the Mach number by varying the density showed only a slight influence on the heat transfer coefficient. The predicted discharge coefficients increased significantly by augmenting the Mach number.

Numerical Characterization of Pressure Drop Across the Manifold of Turbine Casing Cooling System

“…In such configuration Lichtarowicz et al [24] shows that, in term of C d , holes with t=d ¼ 3 behaves as hole with t=d ¼ 2. In the case of t=d ¼ 0:25 (geometry labeled I), the predicted discharge coefficients are close to those related to geometry H for the major part of the holes while, approaching the end of the manifold, the C d remains constant as already pointed out also by Ahmed et al [18,19]. For these reasons, the geometry I was not considered for the definition of the improved correlation.…”

“…More recently, Ahmed et al [18,19] performed some numerical simulation of the flow in a short tube section of an ACC system for a low pressure turbine aimed at the prediction of impingement jet characteristics in form of discharge coefficients, local and spatially averaged Nusselt numbers and heat transfer coefficients. The length-to-diameter ratio of the sharp-edged cylindrical holes, ranged from 0:25 to 2, was also accounted.…”

Low-Pressure Turbine Cooling Systems

“…Various cooling systems nozzles diameters D are considered [2,18,19]. The paper [2] includes a numerical analysis of impingement cooling system with seven different values of cooling nozzles' diameters: D = 0.45 mm; D = 0.5 mm; D = 0.64 mm; D = 0.8 mm; D = 1.6 mm; D = 2.4 mm; D = 3.2 mm.…”

Aerothermal Analysis of a Turbine Casing Impingement Cooling System

“…Comprehensive reviews on this field have been provided by Martin [15] and Han et al [16]. Some recent and very interesting contributions have been made by Ahmed and coworkers [5,6] who have performed some numerical simulations of the flow in a short tube section of an ACC system for a low pressure turbine. The length-to-diameter ratio of the sharp-edged cylindrical nozzles, ranging from 0.25 to 2, was also accounted for.…”

“…The discharge coefficient (C d ) is defined as the ratio of the actual mass flow rate through a hole and the isentropic flow rate. It summarizes all the losses that limit the actual [5].…”