Aeroelastic and Aerodynamic Investigation of a Low Pressure Turbine Under the Influence of a Circumferential Inlet Distortion

Abstract

Modern low pressure turbine (LPT) architectures of aero engines are designed in order to optimize weight, decrease the fuel consumption and noise emissions. This can be achieved with the use of lighter materials or by reducing the size of the engine. In particular, decreasing the axial distances between the blade rows and shortening the turbine centre frame. As a consequence, it becomes more and more important to investigate the influence of inflow circumferential distortions of total pressure and temperature that can be originated by struts, flow injections and measurement instrumentation. This work presents the results of an experimental investigation on the influence of total pressure inflow inhomogeneity on the aerodynamics and on the vibrations of a low pressure turbine stage. The measurements were carried out in a one and a half stage subsonic test turbine facility at nominal engine relevant operating conditions and during speed transient operation, including a resonance crossing. Steady and unsteady aerodynamic measurements were performed with a five-hole-probe (5HP) and a fast response aerodynamic pressure probe (FRAPP) respectively, while the LPT rotor vibration data were acquired using strain gauges applied on different blades, in combination with a telemetry system. Analysis in the frequency domain as well as a curve fitting method were applied to estimate the blades forced response and the critical damping. It will be shown that the distortion creates steady and unsteady aerodynamic alterations, causing direct effects on the rotor vibration characteristics.

Research on the Aerodynamic Performance and Collaborative Optimization Design of the Full-Scale Compact Inlet Chamber of a Nuclear-Powered Steam Turbine

“…Normally, the compact design of power equipment, including power generation steam turbines [4]and gas turbines [5], can reduce manufacturing costs and increase structural intensity. However, a compact design may increase average velocity and flow loss inside the inlet chamber, cause uneven airflow steering, and increase pressure loss.…”

“…(1) Non-uniform intake imposes bending and radial moments on the rotor, which may result in rotor vibrations [6][7][8] and even faults [9], thus affecting bearing safety [10]; (2) Non-uniform intake causes mixed loss in the cascade channel [11][12][13][14] or blast loss [15,16], and a mismatch between the chamber outlet airflow angle and the geometric angle of the first stage static cascade causes shock loss [17]; (3) Non-uniform intake causes an increase in the amplitude of airflow excitation forces on the first-stage dynamic and static lobes [18] and complex excitation force frequencies [5,13,[19][20][21][22].…”

“…The single inlet, dual inlet, and quadruple inlet have been used to throttle governing steam turbines with peripheral inlets [23,28]. Quadruple inlets are usually selected for the high-and medium-pressure chambers of high-power steam turbines, while dual inlets are chosen for the low-pressure cylinder Normally, the compact design of power equipment, including power generation steam turbines [4] and gas turbines [5], can reduce manufacturing costs and increase structural intensity. However, a compact design may increase average velocity and flow loss inside the inlet chamber, cause uneven airflow steering, and increase pressure loss.…”

“…and a mismatch between the chamber outlet airflow angle and the geometric angle of the first stage static cascade causes shock loss [17]; (3) Non-uniform intake causes an increase in the amplitude of airflow excitation forces on the first-stage dynamic and static lobes [18] and complex excitation force frequencies [5,13,[19][20][21][22].…”

Effect of Diffuser Inhomogeneity on Full-Annulus Axial Turbine Performance

“…Turbine inhomogeneity is commonly associated with upstream causes, particularly the combustion chamber (Pyliouras et al, 2012). Previous research has focused on hot-streak propagation (Basol et al, 2011) and the distortion influence on aeroelastic properties (Simonassi et al, 2019). An inhomogeneous pressure field induced by the exit stack, in turn, could similarly affect turbine performance, as disturbances can be transported upstream through the diffuser and act as an outlet boundary condition on the turbine.…”