A NUMERICAL STUDY OF THE EFFECT OF ROUGHNESS ON THE TURBINE BLADE CASCADE PERFORMANCE

摘要

In the present work the numerical simulation of a rectilinear blade cascade with surface roughness up to 100 祄 over different locations of the turbine blade has been performed. The static pressure coefficient over the blade surfaces, mass-averaged loss coefficient and outlet angle at an axial distance of 15% of chord downstream of the cascade outlet, for various levels of roughness are compared with available experimental data and the agreement is good. The computation was extended to roughness at different locations and flow at Mach number 0.6 to 0.9 that is typical of power plant steam turbines. The profile loss coefficient, velocity angle, turbulent kinetic energy, turbulent dissipation rate and Mach number are measured at inlet total pressure of 150 kPa at 15% of the chord downstream of the cascade outlet. The variation of the static pressure coefficient Cp is measured at the blade surface. The suction and pressure surface of the turbine blades are divided into three equal parts leading edge, middle chord and trailing edge for the purpose of comparison. The CFD code FLUENT?has been used for this purpose. It is observed that the effect of roughness on the efficiency of the turbine blade is more on the suction surface than that on the pressure surface. In case of suction surface, mass-averaged profile losses are more when the roughness is provided on the trailing edge than on middle chord and losses are least when the roughness is provided on the leading edge. The pattern of mass average profile losses is, however, different for the roughness on the pressure surface; here the losses are more when the roughness is provided on the leading edge and minimum when roughness is provided on the trailing edge.