Experimental Evaluation of a Wavy Trailing Edge Cooling Design as an Alternative to Pressure Side Cutback Cooling

Abstract

This study measures the film cooling effectiveness along the trailing edge of a turbine blade in a linear cascade. The film cooling effectiveness is measured and analyzed using the pressure sensitive paint (PSP) technique. Two different trailing edge designs are investigated including the standard pressure side cutback and the new alternating discharge design (referred to as a wavy trailing edge design). The alternating discharge design is a new design with a wavy structure between the pressure and suction surfaces at the trailing edge. The new wavy structure allows the coolant to discharge from the trailing edge so that it alternates between the pressure and suction surfaces. Testing is carried out in a five-blade, linear, steady state cascade with inlet and exit Mach numbers of 0.20 and 0.30, respectively. The freestream turbulence intensity is measured to be 10.5% upstream of the blade leading edge. Coolant-to-mainstream mass flow ratios (MFR) vary from 0.30% to 1.25% and coolant to mainstream density ratios (DR) of 1.0, 1.5 and 2.0 are examined. The total pressure loss coefficients are also acquired to compare the aerodynamic loss between the two trailing edge designs. The pressure loss coefficient is acquired by traversing a group of pitot static probes across the blade span in a plane downstream of the trailing edge, resulting in a pressure map at the exit plane. A positive MFR and DR effect is witnessed with almost no change in aerodynamic loss. The results provide the potential of the alternating discharge as a promising trailing edge design and provide gas turbine designers with an improved trailing edge cooling scheme having acceptable aerodynamic loss.