Simulation of Transitional Flow on Low Pressure Turbine Blade With Unsteady Downstream Potential Interaction

2013 ◽  
Author(s):  
Can Ma ◽  
Xin Yuan
Keyword(s):  
Boundary Layer ◽  
Turbine Blade ◽  
Potential Field ◽  
Stokes Equations ◽  
Low Pressure ◽  
Experimental Results ◽  
Transitional Flow ◽  
Free Stream Turbulence ◽  
Low Pressure Turbine ◽  
Transitional Boundary Layer

This paper numerically investigates the transitional flow on a LPT (low pressure turbine) blade with fluctuating downstream potential field. A linear T106 cascade is subjected to an oscillating potential field generated by downstream moving bars. Previous experimental results in open literature showed that the unsteady downstream potential field has an obvious influence on the transitional boundary layer of LPT blade. For the numerical simulations in this paper, the unsteady Reynolds-Averaged Navier-Stokes equations are solved using the commercial software FLUENT. The transition model used in this paper is the γ-Reθ model, which has been validated against a number of transitional flows previously, including the influence of upstream wakes on the transitional boundary layer of T106 turbine blade. The simulation results are first compared to the experimental results in open literature to validate the numerical methods. Two different FSTI (free stream turbulence intensity), 1.6% and 4.0% are investigated with axial spacing between the blade and the downstream bar varying from 50% axial chord to 25% axial chord. To investigate the influence of flow compressibility, two different inlet Mach numbers, 0.02 and 0.2 are simulated. Results show that decreasing the axial spacing has an influence on the unsteady boundary layer separation and transition and the influence is enhanced at elevated inlet Mach number.

Endwall Boundary Layer Development in an Engine Representative Four-Stage Low Pressure Turbine Rig

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Maria Vera ◽  
Elena de la Rosa Blanco ◽  
Howard Hodson ◽  
Raul Vazquez
Keyword(s):  
Boundary Layer ◽  
Leading Edge ◽  
Low Pressure ◽  
The State ◽  
Linear Cascade ◽  
Low Speed ◽  
Cold Flow ◽  
Low Pressure Turbine ◽  
Transitional Boundary Layer ◽  
Passage Vortex

Research by de la Rosa Blanco et al. (“Influence of the State of the Inlet Endwall Boundary Layer on the Interaction Between the Pressure Surface Separation and the Endwall Flows,” Proc. Inst. Mech. Eng., Part A, 217, pp. 433–441) in a linear cascade of low pressure turbine (LPT) blades has shown that the position and strength of the vortices forming the endwall flows depend on the state of the inlet endwall boundary layer, i.e., whether it is laminar or turbulent. This determines, amongst other effects, the location where the inlet boundary layer rolls up into a passage vortex, the amount of fluid that is entrained into the passage vortex, and the interaction of the vortex with the pressure side separation bubble. As a consequence, the mass-averaged stagnation pressure loss and therefore the design of a LPT depend on the state of the inlet endwall boundary layer. Unfortunately, the state of the boundary layer along the hub and casing under realistic engine conditions is not known. The results presented in this paper are taken from hot-film measurements performed on the casing of the fourth stage of the nozzle guide vanes of the cold flow affordable near term low emission (ANTLE) LPT rig. These results are compared with those from a low speed linear cascade of similar LPT blades. In the four-stage LPT rig, a transitional boundary layer has been found on the platforms upstream of the leading edge of the blades. The boundary layer is more turbulent near the leading edge of the blade and for higher Reynolds numbers. Within the passage, for both the cold flow four-stage rig and the low speed linear cascade, the new inlet boundary layer formed behind the pressure leg of the horseshoe vortex is a transitional boundary layer. The transition process progresses from the pressure to the suction surface of the passage in the direction of the secondary flow.

Prediction of Reynolds Number Effects on Low-Pressure Turbines Using a High-Order ILES Method

2019 ◽  
Author(s):  
Marc Bolinches-Gisbert ◽  
David Cadrecha Robles ◽  
Roque Corral ◽  
Fernando Gisbert
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Fourth Order ◽  
Stokes Equations ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
High Order ◽  
Experimental Results ◽  
Numerical Code ◽  
Design System

Abstract A comprehensive comparison between Implicit Large Eddy Simulations (ILES) and experimental results of a modern highlift low-pressure turbine airfoil has been carried out for an array of Reynolds numbers (Re). Experimental data were obtained in a low-speed linear cascade at the Polithecnic University of Madrid using hot-wire anemometry and LDV. The numerical code is fourth order accurate, both in time and space. The spatial discretization of the compressible Navier-Stokes equations is based on a high-order Flux Reconstruction approach while a fourth order Runge-Kutta method is used to march in time the simulations. The losses, pressure coefficient distributions, and boundary layer and wake velocity profiles have been compared for an array of realistic Reynolds numbers. Moreover, boundary layer and wake velocity fluctuations are compared for the first time with experimental results. It is concluded that the accuracy of the numerical results is comparable to that of the experiments, especially for integral quantities such as the losses or exit angle. Turbulent fluctuations in the suction side boundary layer and the wakes are well predicted also. The elapsed time of the is about 140 hours on 40 Graphics Processor Units. The numerical tool is integrated within an industrial design system and reuses pre- and post-processing tools previously developed for another kind of applications. The trend of the losses with the Reynolds number has a sub-critical regime, where the losses scale with Re−1, and a supercrital regime, where the losses scale with Re−1/2. This trend can be seen both, in the simulations and the experiments.

Separation Control on Low-Pressure Turbine Airfoils Using Synthetic Vortex Generator Jets

2003 ◽  
Author(s):  
Ralph J. Volino
Keyword(s):  
Boundary Layer ◽  
Vortex Generator ◽  
Low Pressure ◽  
Turbulent Shear ◽  
Suction Surface ◽  
Local Skin ◽  
Free Stream Turbulence ◽  
Low Pressure Turbine ◽  
Wide Range ◽  
Vortex Generator Jets

Oscillating vortex generator jets have been used to control boundary layer separation from the suction side of a low-pressure turbine airfoil. A low Reynolds number (Re = 25,000) case with low free-stream turbulence has been investigated with detailed measurements including profiles of mean and fluctuating velocity and turbulent shear stress. Ensemble averaged profiles are computed for times within the jet pulsing cycle, and integral parameters and local skin friction coefficients are computed from these profiles. The jets are injected into the mainflow at a compound angle through a spanwise row of holes in the suction surface. Preliminary tests showed that the jets were effective over a wide range of frequencies and amplitudes. Detailed tests were conducted with a maximum blowing ratio of 4.7 and a dimensionless oscillation frequency of 0.65. The outward pulse from the jets in each oscillation cycle causes a disturbance to move down the airfoil surface. The leading and trailing edge celerities for the disturbance match those expected for a turbulent spot. The disturbance is followed by a calmed region. Following the calmed region, the boundary layer does separate, but the separation bubble remains very thin. Results are compared to an uncontrolled baseline case in which the boundary layer separated and did not reattach, and a case controlled passively with a rectangular bar on the suction surface. The comparison indicates that losses will be substantially lower with the jets than in the baseline or passively controlled cases.

Numerical Investigation of Contrasting Flow Physics in Different Zones of a High-Lift Low-Pressure Turbine Blade

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Jiahuan Cui ◽  
V. Nagabhushana Rao ◽  
Paul Tucker
Keyword(s):  
Boundary Layer ◽  
Turbine Blade ◽  
Low Pressure ◽  
The State ◽  
Suction Surface ◽  
Flow Physics ◽  
Pressure Surface ◽  
Low Pressure Turbine ◽  
Flow Features ◽  
The Impact

Using a range of high-fidelity large eddy simulations (LES), the contrasting flow physics on the suction surface, pressure surface, and endwalls of a low-pressure turbine (LPT) blade (T106A) was studied. The current paper attempts to provide an improved understanding of the flow physics over these three zones under the influence of different inflow boundary conditions. These include: (a) the effect of wakes at low and high turbulence intensity on the flow at midspan and (b) the impact of the state of the incoming boundary layer on endwall flow features. On the suction surface, the pressure fluctuations on the aft portion significantly reduced at high freestream turbulence (FST). The instantaneous flow features revealed that this reduction at high FST (HF) is due to the dominance of “streak-based” transition over the “Kelvin–Helmholtz” (KH) based transition. Also, the transition mechanisms observed over the turbine blade were largely similar to those on a flat plate subjected to pressure gradients. On pressure surface, elongated vortices were observed at low FST (LF). The possibility of the coexistence of both the Görtler instability and the severe straining of the wakes in the formation of these elongated vortices was suggested. While this was true for the cases under low turbulence levels, the elongated vortices vanished at higher levels of background turbulence. At endwalls, the effect of the state of the incoming boundary layer on flow features has been demonstrated. The loss cores corresponding to the passage vortex and trailing shed vortex were moved farther from the endwall with a turbulent boundary layer (TBL) when compared to an incoming laminar boundary layer (LBL). Multiple horse-shoe vortices, which constantly moved toward the leading edge due to a low-frequency unstable mechanism, were captured.

scholarly journals Intermittent Behavior of the Separated Boundary Layer Along the Suction Surface of a Low Pressure Turbine Blade Under Periodic Unsteady Flow Conditions

2005 ◽  
Author(s):  
B. O¨ztu¨rk ◽  
M. T. Schobeiri ◽  
David E. Ashpis
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Turbine Blade ◽  
Low Pressure ◽  
Boundary Layer Transition ◽  
Wake Flow ◽  
Unsteady Boundary Layer ◽  
Flow Conditions ◽  
Suction Surface ◽  
Low Pressure Turbine

The paper experimentally and theoretically studies the effects of periodic unsteady wake flow and aerodynamic characteristics on boundary layer development, separation and re-attachment along the suction surface of a low pressure turbine blade. The experiments were carried out at Reynolds number of 110,000 (based on suction surface length and exit velocity). For one steady and two different unsteady inlet flow conditions with the corresponding passing frequencies, intermittency behavior were experimentally and theoretically investigated. The current investigation attempts to extend the intermittency unsteady boundary layer transition model developed in previously to the LPT cases, where separation occurs on the suction surface at a low Reynolds number. The results of the unsteady boundary layer measurements and the intermittency analysis were presented in the ensemble-averaged, and contour plot forms. The analysis of the boundary layer experimental data with the flow separation, confirms the universal character of the relative intermittency function which is described by a Gausssian function.

Prediction of Reynolds Number Effects on Low-Pressure Turbines Using a High-Order ILES Method

2020 ◽  
Vol 142 (3) ◽  
Author(s):  
M. Bolinches-Gisbert ◽  
David Cadrecha Robles ◽  
Roque Corral ◽  
Fernando Gisbert
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Fourth Order ◽  
Stokes Equations ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
High Order ◽  
Experimental Results ◽  
Numerical Code ◽  
Design System

Abstract A comprehensive comparison between implicit large eddy simulations (ILES) and experimental results of a modern high-lift low-pressure turbine airfoil has been carried out for an array of Reynolds numbers (Re). Experimental data were obtained in a low-speed linear cascade at the Polytechnic University of Madrid using hot-wire anemometry and laser-Doppler velocimetry (LDV). The numerical code is fourth-order accurate, both in time and space. The spatial discretization of the compressible Navier–Stokes equations is based on a high-order flux reconstruction approach while a fourth-order Runge–Kutta method is used to march in time the simulations. The losses, pressure coefficient distributions, and boundary layer and wake velocity profiles have been compared for an array of realistic Reynolds numbers. Moreover, boundary layer and wake velocity fluctuations are compared for the first time with experimental results. It is concluded that the accuracy of the numerical results is comparable to that of the experiments, especially for integral quantities such as the losses or exit angle. Turbulent fluctuations in the suction side boundary layer and the wakes are well predicted too. The elapsed time of the simulations is about 140 h on 40 graphics processor units. The numerical tool is integrated within an industrial design system and reuses pre- and post-processing tools previously developed for another kind of applications. The trend of the losses with the Reynolds number has a sub-critical regime, where the losses scale with Re−1, and a supercritical regime, where the losses scale with Re−1/2. This trend can be seen both in the simulations and in the experiments.

Loss Mechanism of Low-Pressure Turbine Secondary Flows Due to Different Incoming Boundary Layers

2020 ◽  
Vol 142 (10) ◽  
Author(s):  
Jiangdong Hou ◽  
Chao Zhou
Keyword(s):  
Boundary Layer ◽  
Stokes Equations ◽  
Vortex Pair ◽  
Low Pressure ◽  
Secondary Flows ◽  
Dominant Factor ◽  
Loss Mechanism ◽  
Turbulent Dissipation ◽  
Low Pressure Turbine ◽  
The Mean

Abstract In high bypass ratio engines, the flow exits the interturbine duct (ITD) and enters the low-pressure (LP) turbine. This paper aims to understand the effects of the boundary layer at the exit of ITD on the endwall secondary flows and loss of the first blade row in a low-pressure turbine. From the Navier–Stokes equations, the loss is decomposed into the parts generated by the mean vortex as well as turbulence theoretically. The result of computational fluid dynamics (CFD) shows that the incoming boundary layer from the ITD increases the total pressure loss coefficient by 14% compared to the case with uniform inlet condition. Although the distribution of the secondary vortices is strongly affected by the inlet boundary layer, the loss generated by the mean vortex within the blade passage is hardly affected. The analysis based on the turbulent dissipation shows that the dominant factor leading to the loss increase is the turbulent dissipation downstream of the blade trailing edge (TE) near the hub. The mixing process of the wake and the strong counter-rotating vortex pair (CVP) increases the turbulent dissipation significantly. It is also found that a simplified incoming boundary layer defined by the Prandtl's one-seventh power law can not reproduce the complex effects of the incoming boundary layer from the ITD.

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