Aerodynamic Analysis of an Innovative Low Pressure Vane Placed in an s-Shape Duct

Abstract

In this paper the aerodynamics of an innovative multisplitter low pressure (LP) stator downstream of a high pressure turbine stage is presented. The stator row, located inside a swan necked diffuser, is composed of 16 large structural vanes and 48 small airfoils. The experimental characterization of the steady and unsteady flow fields was carried out in a compression tube rig under engine representative conditions. The one-and-a-half turbine stage was tested at three operating regimes by varying the pressure ratio and the rotational speed. Time-averaged and time-accurate surface pressure measurements are used to investigate the aerodynamic performance of the stator and the complex interaction mechanisms with the high pressure (HP) turbine stage. Results show that the strut blade has a strong impact on the steady and unsteady flow fields of the small vanes depending on the vane circumferential position. The time-mean pressure distributions around the airfoils show that the strut influence is significant only in the leading edge region. At off-design condition (higher rotor speed) a wide separated region is present on the strut pressure side and it affects the flow field of the adjacent vanes. A complex behavior of the unsteady surface pressures was observed. Up to four pressure peaks are identified in the time-periodic signals. The frequency analysis also shows a complex structure. The spectrum distribution depends on the vane position. The contribution of the harmonics is often larger than the fundamental frequency. The forces acting on the LP stator vanes are calculated. The results show that higher forces act on the small vanes but largest fluctuations are experienced by the strut. The load on the whole stator decreases 30% as the turbine pressure ratio is reduced by approximately 35%.

Impact of a multi-splitter vane configuration on the losses in a 1.5 turbine stage

“…Comparison between the multi-splitter and the conventional LPV geometry shows that the strut airfoils primarily affect the flow field in the crown region of the aero-vanes. In fact, the struts modify the incidence angle of the aerovanes depending on the circumferential position of the aero-vane, since the flow is turned inside the strut passage upstream of the aero-vanes [13]. When the stator runs at low-pressure ratio, the incidence angle changes drastically from À7 to 32 , which causes a high diffusion rate close to the shroud due to the existence of the S-shaped duct and leading edge curvature.…”

“…When the stator runs at low-pressure ratio, the incidence angle changes drastically from À7 to 32 , which causes a high diffusion rate close to the shroud due to the existence of the S-shaped duct and leading edge curvature. Therefore, the flow separates on the pressure side of the strut [13]. Figure 6 represents the flow angle difference between the conventional and splitter configuration over a strut pitch.…”

“…This is a good compromise between the geometry for optimal diffusion rate in the duct and the geometry that prevents boundary layer separation, particularly at the tip section. Experimental investigations were performed at the von Karman Institute compression tube turbine test rig [13]. The experimental facility is able to reproduce the actual engine non-dimensional parameters, namely, the Mach number, the Reynolds number, and the blade to gas temperature ratios.…”

Mitigation of Turbine Vane Shock Waves Through Trailing Edge Cooling

“…Impingement of trailing-edge shocks generated at nozzle vanes causes heat transfer oscillations over the surface of rotor blades [4], which leads to stress variations originated by inhomogeneous and transient temperature distributions over the blade geometries referred as airfoil load shakedown [5]. Also, mechanical fatigue caused by unsteady flow structures is a dominant factor determining the life time of turbomachinery parts [6]. Hence, transient variations of high intensity shock waves correspond to oscillations of extreme localized stresses on rotor blades of about 30~40% of the mean level [7].…”

Flow Evolution Through a Turning Midturbine Frame with Embedded Design

“…The basic idea was to merge the struts and the LP vanes in one multisplitter component. Such a concept was investigated at the von Kármán Institute (e.g., Lavagnoli et al [10]) and at the Institute for Thermal Turbomachinery and Machine Dynamics. Spataro et al [11,12] proposed a setup embedding two splitters into the strut channel of an existing turning midturbine frame placed between two counter-rotating turbines.…”