Periodic Unsteady Inflow Research Articles

Nonintrusive Experimental Aeroelastic Analysis of a Highly Flexible Wing

The aeroelastic response of the Delft–Pazy wing to steady and periodic unsteady inflow conditions is analyzed experimentally. The Delft–Pazy wing is a highly flexible wing model based on the benchmark Pazy wing (Avin, O., Raveh, D. E., Drachinsky, A., Ben-Shmuel, Y., and Tur, M., “Experimental Aeroelastic Benchmark of a Very Flexible Wing,” AIAA Journal, Vol. 60, No. 3, 2022, pp. 1745–1768) and exhibits wingtip displacements of more than 24% of the span in the present study. The nonintrusive measurements are performed with an integrated optical approach that provides combined measurements of the structural response of the wing and the unsteady flowfield around it. The aeroelastic loads acting on the wing are derived using physical models and validated against force balance measurements, showing a good agreement for all considered inflow conditions. The analysis of the aeroelastic response of the wing to the unsteady inflow produced by a gust generator shows that both structural and aerodynamic responses depend strongly on the frequency of the gust. The results of this study provide a characterization of the aeroelastic behavior of the Delft–Pazy wing and can serve as a reference for the development of novel and improved nonlinear aeroelastic simulation models.

Effects of Periodic Unsteady Inflow on Film Cooling and Heat Transfer on Highly Loaded High Pressure Turbine Blades With Flow Separation

Film cooling experiments were run at the high-speed cascade wind tunnel of the University of the Federal Armed Forces Munich. The investigations were carried out on a linear cascade of highly loaded turbine blades. The main targets of the tests were to assess the film cooling effectiveness and the heat transfer in zones with main flow separation. The previous cascade was designed to have a large zone with flow separation on the pressure side starting at the leading edge and reaching up to approximately half of the axial chord. This cascade was changed for a new design with a larger pitch to chord ratio in order to set the focus on flow separation on the suction side. This increased pitch forces a massive separation on the suction side due to strong shocks. The flow separation is controlled with aid of vortex generating jets in order to reduce the total pressure loss caused by it. Film cooling is provided on the suction side upstream of the vortex generating jets. The measurements comprise of blade loading, profile loss, adiabatic film cooling effectiveness, and heat transfer coefficient under two Mach numbers at a Reynolds number of 390,000. In a previous publication detailed results with homogeneous inflow where shown. Now, the focus is set on the effects of periodic unsteady wakes resulting from bars moving upstream of the cascade. These moving bars create a periodic unsteady inflow similar to the interaction between stator and rotor in the machine. It is shown how these wakes have significant influence on the heat transfer in the acceleration region of the suction side and affect the adiabatic film cooling effectiveness upstream of the shock.

Calculation of Steady and Periodic Unsteady Blade Surface Heat Transfer in Separated Transitional Flow

In this work, aerothermal investigations of a highly loaded HP turbine blade are presented. The purpose of such investigations is to improve the physical understanding of the heat transfer in separated flow regions, with the final goal of optimizing cooling configurations for aerodynamically highly loaded turbine designs. The analysis is focused on the T120 cascade, that was recently tested experimentally in the framework of the European project AITEB-2 (Aero-thermal Investigation of Turbine Endwalls and Blades). Such a cascade has a relatively low solidity that is responsible for the formation of a laminar separation bubble on the suction side of the blade. Separated-flow transition and transonic conditions downstream of the throat result in a flow configuration that is very challenging for traditional RANS solvers. Moreover, the separated flow transition pattern was found to have a strong impact on both the aerodynamic and thermal aspects. The study was carried out using a novel three-equation, transition-sensitive, turbulence model. It is based on the coupling of an additional transport equation for the laminar kinetic energy to the Wilcox k - ω model. Such an approach allows one to take into account the increase of the nonturbulent fluctuations in the pretransitional and transitional region. Comprehensive aerodynamic and heat transfer measurements were available for comparison purposes. In particular, heat transfer measurements cover different Mach and Reynolds numbers, in both steady and periodic unsteady inflow conditions. A detailed comparison between measurements and computations is presented, and the impact of transition-related aspects on the surface heat transfer is discussed.

Film Cooling Effectiveness Measurements With Periodic Unsteady Inflow on Highly Loaded Blades With Main Flow Separation

Abstract Film cooling experiments were performed using a highly loaded high pressure turbine blade blade linear cascade. A large region with main flow separation is found on the pressure side and film cooling is provided into this area with three rows of either cylindrical or fan-shaped holes. The measurements comprise adiabatic film cooling effectiveness and profile static pressure measurements. The surface temperature was acquired with thermochromatic liquid crystals and using a hue to temperature correlation. The results shown are for variations in main flow Mach and Reynolds numbers at engine relevant levels and of coolant mass flows. The results for steady and periodic unsteady inflows with highly turbulent wakes created by cylindrical bars moving upstream in a plane parallel to the cascade are compared as two-dimensional surface plots, laterally averaged film cooling effectiveness and overall effectiveness over the entire surface.

Unsteady Periodic Behavior of a Disturbed Tip-Leakage Flow

The unsteady periodic behavior of a tip-leakage flow downstream of a simulated axial compressor rotor has been studied. A linear cascade wind tunnel has been adapted to model this situation. The wind tunnel features a moving endwall to simulate the relative motion between the rotor and casing and vortex generators attached to the moving end wall that produce an idealized periodic unsteady vortical inflow simulating the flow shed by the casing junctions of a row of inlet guide vanes. Detailed three-component mean-velocity and turbulence measurements have been made just downstream of the blade trailing edges and phase averaged with respect to the relative position of the blades and vortex generator wakes. The comparison between the disturbed and undisturbed tip-leakage flows shows that on time average the vortical inflow does not change the flowfield much, except for a slight decrease in streamwise velocity deficit and a small increase in turbulence kinetic energy in the tip-leakage vortex region. However, phase-averaged measurements reveal that the inflow vortices produce significant fluctuations in the size, strength, structure, and position of the tip-leakage vortex, despite the fact that they are about two orders weaker than the tip-leakage vortex. It is hypothesized that the unsteady vortical inflow influences the tip-leakage vortex at its formation, by periodically disturbing the shedding of vorticity from the blade tip.

Effect of Reynolds number, turbulence level and periodic wake flow on heat transfer on low pressure turbine blades.

The development of effective cooling methods is of major importance for the design of new gas turbines blades. The conception of optimal cooling schemes requires a detailed knowledge of the heat transfer processes on the blade's surfaces. The thermal load of turbine blades is predominantly determined by convective heat transfer which is described by the local heat transfer coefficient. Heat transfer is closely related to the boundary layer development along the blade surface and hence depends on various flow conditions and geometrical parameters. Particularly Reynolds number, pressures gradient and turbulence level have great impact on the boundary layer development and the according heat transfer. Therefore, in the present study, the influence of Reynolds number, turbulence intensity, and periodic unsteady inflow on the local heat transfer of a typical low pressure turbine airfoil is experimentally examined in a plane cascade.