Characteristics of a Turbine Cascade at Low Reynolds Numbers

Abstract

The aerodynamic characteristics of turbine cascades are thought to be relatively satisfactory due to the favorable pressure of the accelerating flow. But within the low Reynolds number region of 50,000 where the 300kW ceramic gas turbines which are being developed under the New-Sunshine Project of Japan operate, the characteristics such as boundary layer separation and reattachment which lead to prominent power losses cannot be easily predicted. In this research, experiments have been conducted to evaluate the performance of a linear two dimensional turbine cascade. Surface pressure distributions of the airfoil were measured for a range of blade chord Reynolds numbers from 40,000 to 160,000 (at inlet), and at 1.3% inlet turbulence intensity. In addition, the wake of the cascade was measured simultaneously using a five hole pilot tube. Traverses of the wake show that there is a drastic increase in the mean total pressure loss at the wake between the Reynolds number of 80,000 to 40,000, and in some conditions, a rise as much as 10% was confirmed. Thus, in accordance with the pressure distribution of the surface of the airfoil, a relation between the total pressure loss and the length of the laminar separation bubble formed on the airfoil could be seen.

Aerodynamics of a Transitioning Turbine Stator Over a Range of Reynolds Numbers

“…Variations in the transition location strongly affect the surface heat transfer, and can significantly affect the aerodynamics. If suction surface transition does not occur upstream of the throat, there is the likelihood of laminar separation, and consequent significant decrease in blade row aerodynamic efficiency, Murata et al (1997). Actual turbine blades see a high level of turbulence.…”

Characteristics of an Annular Turbine Cascade at Low Reynolds Numbers

“…Although these detailed experimental investigations are well done in themselves, not much attention was paid to the effect of Reynolds number. Recently, several studies focused on the characteristics of LP turbine at low Reynolds number were published (Curis, 1996, Schulte, 1996, Murata, 1997, Murawski, 1997, Vijayaraghavan, 1988, but yet much remains unclear. In addition, these researches were concerned with linear (two-dimensional) cascades, thus research with annular (three-dimensional) cascade at low Reynolds number region has not yet been realized.…”