Analysis of Flow Characteristic of Transonic Tandem Rotor Airfoil and Its Optimization

Tandem blade technology has become an effective method to break the load limit of conventional aerodynamic configurations. To expand the application range of tandem blades, the supersonic tandem blade flow characteristic was studied and an optimal design was conducted by using a computational fluid dynamics (CFD) solver, with an inflow Mach number of 1.2. The main conclusions follow: (1) the tandem blade loss is difficult to control because of the complicated flow structures with supersonic inflow; (2) the forward blade loss dominates the tandem blade overall loss in the whole operating conditions; and (3) the tandem blade profile was optimized by considering the aerodynamic interaction between forward and aft blade. The numerical simulation results show that the total pressure loss declines by 20% at the design point, and the incidence range increases by about 0.5°.

Effect of Unguided Turning Angle and Trailing Edge Shape on Cooled Blade Loss

A significant part of the overall loss in modern gas turbines is the trailing edge loss. This loss is, more strongly than other constituents, affected by operation, because the trailing edge can significantly change its shape due to degradation. Also by manufacturing of new parts and reconditioning the same tolerances as in other parts of blade lead to higher deviations of aerodynamic characteristics. Therefore the understanding of trailing edge loss generation mechanisms is of utmost importance for a sound blade design. In this work the results of combined experimental and numerical investigation of the trailing edge impact on the transonic cooled blade loss are presented. This study comprises the investigation of the unguided flow angle and the trailing edge shape on the profile losses and a base pressure. The unguided flow angle characterizes the curvature distribution on the aerofoil suction side. The numerical and experimental investigation of transonic cooled turbine cascades have shown that the increase of the unguided flow angle results in loss reduction due to increase of the base pressure downstream of the trailing edge. At the same time the deviation of the trailing edge from a round shape has detrimental effect on performance and conducted investigations allow quantification of this effect. The measurements were performed in a transonic wind tunnel and numerical simulations were done using in-house 2D Navier-Stokes code. The comparison of calculations with measurements showed that they are in reasonable agreement. The validated numerical procedure has been used for demonstration of possibility to reduce loss in aerofoil with thick trailing edge by tuning of the unguided flow angle. The use of the thick trailing edges at HP cooled turbines reduces restriction on tolerances, improves of manufacturability and reduces cost.

Compressor Blade Modelling Under Highly Negative Incedence

This paper investigates performance prediction techniques for compressor blades operating under highly negative incidence angle which is typical during engine groundstarts or windmilling relights. Although this is a very frequently occurring situation during the life of an aero engine, turbomachinery components are rarely tested under those conditions in the sake of resource saving. However, performance engineers require some knowledge of generic blade loss coefficients under those conditions for the preliminary estimation of the groundstart or relight capability of the engine which is also linked to design decisions such as the volume of the combustion chamber. A blade element concept is employed to break a 3D compressor blade design down to a number of 2D cross sections and study them separately using a CFD derived 2D blade loss coefficient database. Several different ways to synthesize the 3D blade out of the 2D sections are herein presented based on different expressions of blade aerodynamic coefficients. An investigation based on the expressions of the aerodynamic coefficients is conducted in order to justify the applicability of the blade element theory at such off-design conditions. The most suitable parameter set to represent a three dimensional blade design by a number of radially stacked two dimensional profiles is identified. The analysis shows that the approach based on pressure change and tangential force coefficients can more adequately approximate the performance of the 3D blade and therefore can be safely employed for a preliminary off-design blade performance studies.