Unsteady Numerical Investigation of Blade Tip Leakage, Part 1: Time-Averaged Results

Abstract

In today's modern gas turbine engines, the region between the rotor and the stationary shroud has the most extreme fluid-thermal conditions in the entire turbine and is characterized by a periodically unsteady threedimensional flowfield. The purpose of the present work is to conduct an unsteady study of the tip leakage flow adjacent to the shroud in real gas turbine engines using an in-house industrial computational fluid dynamics code. Both time-averaged and time-dependent data for the velocity, temperature, and mass flow rate in the tip clearance region are presented in parts 1 and 2, respectively. In part 1, it was found that near the pressure side of the tip clearance region and near the blade tip on the suction side, the leakage flow is dominant, whereas opposing flows entering through the suction side dominate near the shroud and at the suction side. This opposing flow is the combined effect of the shroud relative motion and the crossflow originating from the adjacent blade passage on the suction side. A small recirculation region was observed above the rotor passage and was attributed to the bladepassage crossflow interacting with the high-pressure region found at the suction side of the blade. This high-pressure region is caused by the combined effect of the crossflow with the shroud boundary-layer flow interacting with the tip leakage flow inside the tip clearance region. Nomenclature b = blade span C x = blade axial chord h = tip clearance height M = Mach number P = pressure r = radial coordinate T = temperature v = velocity vector W = mass flow rate x = axial coordinate y = Cartesian coordinate oriented along the circumferential direction z = Cartesian coordinate oriented along the radial direction Subscripts aw = adiabatic wall c = core flow o = stagnation properties rel = relative s = isentropic

Tip Leakage Flow and Heat Transfer on Turbine Stage Tip and Casing: Effect of Unsteady Stator–rotor Interactions

“…The fluctuating force on the rotor blade indicated the effect of the separated vortices inherited by the upstream vane wake. Phutthavong et al (2008aPhutthavong et al ( , 2008b Three distinct regions of the high heat transfer rate on the casing were observed for the uniform inlet temperature case. Two of them were seen along the path of the unsteady vane wake, while the other high heat transfer regions coincided with the traveling shock wave that originated from the vane trailing edge.…”

Aerothermal and aerodynamic performance of turbine blade squealer tip under the influence of guide vane passing wake

“…Rahman et al 23 performed simulations on a single-stage turbine and compared transient, averaged, and steady results, showing HTC and leakage flow are highly time-independent. Phutthavong et al 24 carried out 3 D unsteady simulations on a certain turbine stage and explored the effect of rotational speed, tip clearance, etc. on leakage flow, emphasizing on the variation of unsteady results.…”

“…Phutthavong et al. 24 carried out 3 D unsteady simulations on a certain turbine stage and explored the effect of rotational speed, tip clearance, etc. on leakage flow, emphasizing on the variation of unsteady results.…”

Tip Leakage Flow and Heat Transfer on Turbine Blade Tip and Casing, Part 1: Effect of Tip Clearance Height and Rotation Speed

“…Both numerical and experimental studies were conducted using simplified flow conditions, such as, stationary blade, low pressure ratio, and low inlet temperature. Both steady and unsteady simulations of blade tip leakage flow in a single stage gas turbine were performed by Phutthavong et al (2008aPhutthavong et al ( , 2008b) using a non commercial CFD solver called Nistar. The shear stress transport (SST)   k turbulence model was selected in order to capture the flow characteristics in the tip gap region.…”

“…The MT1 is a full-size, high-pressure, un-shrouded, one-stage research turbine. In the authors' research group, a full-size single stage gas turbine was modeled (Phutthavong et al, 2008a) based on the available limited information of the MT1 turbine (especially, the blade tip geometry in Chana and Jones, 2003). The turbine geometry is not identical to that of the MT1 turbine but its length is close to that of Chana and Jones (2003).…”