Influence of Two-Dimensional vs. Discrete Disturbances on Separating Low Pressure Turbine Boundary Layers

2007 ◽  
Author(s):  
Daniel Reimann ◽  
Matthew Bloxham ◽  
Jonathon Pluim ◽  
Jeffrey Bons
Keyword(s):  
Boundary Layers ◽  
Low Pressure ◽  
Two Dimensional ◽  
Low Pressure Turbine

scholarly journals Predictions of Separated and Transitional Boundary Layers Under Low-Pressure Turbine Airfoil Conditions Using an Intermittency Transport Equation

2003 ◽  
Vol 125 (3) ◽  
pp. 455-464 ◽  
Author(s):  
Y. B. Suzen ◽  
P. G. Huang ◽  
Lennart S. Hultgren ◽  
David E. Ashpis
Keyword(s):  
Transport Equation ◽  
Boundary Layers ◽  
Eddy Viscosity ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
Equation Model ◽  
Intermittent Behavior ◽  
Low Pressure Turbine ◽  
Transitional Boundary Layer ◽  
Intermittency Factor

A new transport equation for the intermittency factor was proposed to predict separated and transitional boundary layers under low-pressure turbine airfoil conditions. The intermittent behavior of the transitional flows is taken into account and incorporated into computations by modifying the eddy viscosity, μt, with the intermittency factor, γ. Turbulent quantities are predicted by using Menter’s two-equation turbulence model (SST). The intermittency factor is obtained from a transport equation model, which not only can reproduce the experimentally observed streamwise variation of the intermittency in the transition zone, but also can provide a realistic cross-stream variation of the intermittency profile. In this paper, the intermittency model is used to predict a recent separated and transitional boundary layer experiment under low pressure turbine airfoil conditions. The experiment provides detailed measurements of velocity, turbulent kinetic energy and intermittency profiles for a number of Reynolds numbers and freestream turbulent intensity conditions and is suitable for validation purposes. Detailed comparisons of computational results with experimental data are presented and good agreements between the experiments and predictions are obtained.

Evaluation of RANS Transition Modeling for High Lift LPT Flows at Low Reynolds Number

2013 ◽  
Author(s):  
Kevin Keadle ◽  
Mark McQuilling
Keyword(s):  
Reynolds Number ◽  
Total Pressure ◽  
Current Model ◽  
Pressure Coefficient ◽  
Low Pressure ◽  
Two Dimensional ◽  
High Lift ◽  
Low Pressure Turbine ◽  
Low Reynolds ◽  
Turbine Airfoils

High lift low pressure turbine airfoils have complex flow features that can require advanced modeling capabilities for accurate flow predictions. These features include separated flows and the transition from laminar to turbulent boundary layers. Recent applications of computational fluid dynamics based on the Reynolds-averaged Navier-Stokes formulation have included modeling for attached and separated flow transition mechanisms in the form of empirical correlations and two- or three-equation eddy viscosity models. This study uses the three-equation model of Walters and Cokljat [1] to simulate the flow around the Pack B and L2F low pressure turbine airfoils in a two-dimensional cascade arrangement at a Reynolds number of 25,000. This model includes a third equation for the development of pre-transitional laminar kinetic energy (LKE), and is an updated version of the Walters and Leylek [2] model. The aft-loaded Pack B has a nominal Zweifel loading coefficient of 1.13, and the front-loaded L2F has a nominal loading coefficient of 1.59. Results show the updated LKE model improves predicted accuracy of pressure coefficient and velocity profiles over its previous version as well as two-equation RANS models developed for separated and transitional flows. Transition onset behavior also compares favorably with experiment. However, the current model is not found suitable for wake total pressure loss predictions in two-dimensional simulations at extremely low Reynolds numbers due to the predicted coherency of suction side vortices generated in the separated shear layers which cause a local gain in wake total pressure.

Experimental and Numerical Verification of the Core-Flow in a New Low-Pressure Turbine

2016 ◽  
Author(s):  
Michael Henke ◽  
Lars Wein ◽  
Tim Kluge ◽  
Yavuz Guendogdu ◽  
Marc Heinz-Otto Biester ◽  
...  
Keyword(s):  
Flow Field ◽  
Low Pressure ◽  
Numerical Verification ◽  
Two Dimensional ◽  
Core Flow ◽  
Low Pressure Turbine ◽  
The Core ◽  
Blade Row ◽  
Unsteady Effects ◽  
Blade Row Interaction

The flow field in modern axial turbines is non-trivial and highly unsteady due to secondary flow and blade row interaction. In recent years, existing design-tools like two-dimensional flow solvers as well as fully three-dimensional CFD methods have been validated for the assumption of a quasi-steady flow field. Since the inevitable unsteadiness of the flow field has a direct impact on unsteady loss generation and work transfer, existing design methods stand in need of validation for local unsteady effects within the flow field. In order to clearly separate end-wall losses from those generated by blade row interaction within the blade passage, a two-dimensional core-flow is essential for the investigation. Hence, a new 1.5-stage high aspect ratio low pressure turbine has been designed to determine the intensity of core-flow blade row interaction for different axial gaps. First, inlet and outlet conditions of the test rig are evaluated with regard to homogeneity of the flow parameters in their radial and circumferential distributions. Secondly, the measurement data gained from rig tests have been applied as boundary conditions to time-averaged numerical computations. The flow field analysis for two different axial gaps focuses on the verification of the core flow. The authors show that the new turbine has been successfully verified using both test data and the numerical predictions, serving as a precondition for the validation of the numerical model for unsteady effects within the core-flow.

Effect of Sector Mode Shape Variation on the Aerodynamic Stability of a Low-Pressure Turbine Sectored Vane

2003 ◽  
Author(s):  
Olga V. Chernysheva ◽  
Torsten H. Fransson ◽  
Robert E. Kielb ◽  
John Barter
Keyword(s):  
Turbine Blades ◽  
Low Pressure ◽  
Mode Shapes ◽  
Two Dimensional ◽  
Shape Variation ◽  
Aerodynamic Stability ◽  
Flow Solver ◽  
Low Pressure Turbine ◽  
Influence Coefficients

The paper presents a method to investigate the flutter appearance in a cascade, where blades are connected together in a number of identical sectors. The key parameters of the method are vibration amplitudes and mode shapes of the blades belonging to the same sector. The aerodynamic response from a sectored vane cascade is calculated based on the aerodynamic work influence coefficients of freestanding blades performed with two-dimensional inviscid linearized flow solver. A case study based upon the presented methodology shows that, despite stabilizing effect of tying blades together into sectors, a sectored vane consisting of six low-pressure turbine blades vibrating with real single modes, and identical amplitudes can be unstable at realistic design conditions.

Numerical and Experimental Studies on Separated Boundary Layers Over Ultra-High Lift Low-Pressure Turbine Cascade Airfoils With Variable Solidity: Effects of Free-Stream Turbulence

2008 ◽  
Author(s):  
Ken-Ichi Funazaki ◽  
Kazutoyo Yamada ◽  
Yasuhiro Chiba ◽  
Nozomi Tanaka
Keyword(s):  
Boundary Layers ◽  
Free Stream ◽  
Separation Bubble ◽  
Experimental Studies ◽  
Low Pressure ◽  
Freestream Turbulence ◽  
High Lift ◽  
Free Stream Turbulence ◽  
Low Pressure Turbine ◽  
Turbine Airfoils

This paper deals with LES investigation, along with measurements, on the interaction between inlet freestream turbulence and boundary layers with separation bubble over ultra-high lift low-pressure turbine airfoils. The cross section of the test airfoils is typical for highly-loaded LP turbines for civil aeroengines. The solidity of the cascade can be reduced by increasing the airfoil pitch by at least 25%, while maintaining the throat in the blade-to-blade passage. Reynolds number examined is 57,000, based on chord length and averaged exit velocity. Free-stream turbulence is about 0.85% (no grid condition) and 2.1% (with grid condition). Hot-wire probe measurements of the boundary layer are carried out to obtain time-averaged and time-resolved characteristics of the boundary layers under the influence of the freestream turbulence. A newly developed probe positioning tool, which is installed downstream of the cascade with minimal blockage, enables precise probe positioning along lines normal to the airfoil surface. Numerical analysis based on high-resolution LES (Large-Eddy Simulation) is executed to enhance the understanding of the flow field around the Ultra-High Lift and High Lift LP turbine airfoils. Emphasis is placed on the relationship of inherent instability of the shear layer of the separation bubble and the free-stream turbulence. Standard Smagorinsky model is employed for subgrid scale modeling. The flow solver used is an in-house code that was originally developed by one of the authors as FVM (Finite Volume Method)-based fully implicit and time-accurate Reynolds-Averaged Navier-Stokes code. Homogeneous isotropic turbulence created with SNGR (Stochastic Noise Generation and Radiation) method using von Karman-Pao turbulent energy spectrum is applied in the present study for the emulation of inlet turbulence.

Influence of Jet-Induced Transition on Separating Low-Pressure Turbine Boundary Layers

2007 ◽  
Vol 23 (5) ◽  
pp. 996-1006 ◽  
Author(s):  
D. Reimann ◽  
M. Bloxham ◽  
K. L. Crapo ◽  
J. D. Pluim ◽  
J. P. Bons
Keyword(s):  
Boundary Layers ◽  
Low Pressure ◽  
Low Pressure Turbine

scholarly journals Measurements in Separated and Transitional Boundary Layers Under Low-Pressure Turbine Airfoil Conditions

2000 ◽  
Vol 123 (2) ◽  
pp. 189-197 ◽  
Author(s):  
Ralph J. Volino ◽  
Lennart S. Hultgren
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Pressure Gradient ◽  
Boundary Layers ◽  
Free Stream ◽  
Separation Bubble ◽  
Low Pressure ◽  
Mean Velocity ◽  
Free Stream Turbulence ◽  
Low Pressure Turbine

Detailed velocity measurements were made along a flat plate subject to the same dimensionless pressure gradient as the suction side of a modern low-pressure turbine airfoil. Reynolds numbers based on wetted plate length and nominal exit velocity were varied from 50,000 to 300,000, covering cruise to takeoff conditions. Low and high inlet free-stream turbulence intensities (0.2 and 7 percent) were set using passive grids. The location of boundary-layer separation does not depend strongly on the free-stream turbulence level or Reynolds number, as long as the boundary layer remains nonturbulent prior to separation. Strong acceleration prevents transition on the upstream part of the plate in all cases. Both free-stream turbulence and Reynolds number have strong effects on transition in the adverse pressure gradient region. Under low free-stream turbulence conditions, transition is induced by instability waves in the shear layer of the separation bubble. Reattachment generally occurs at the transition start. At Re=50,000 the separation bubble does not close before the trailing edge of the modeled airfoil. At higher Re, transition moves upstream, and the boundary layer reattaches. With high free-stream turbulence levels, transition appears to occur in a bypass mode, similar to that in attached boundary layers. Transition moves upstream, resulting in shorter separation regions. At Re above 200,000, transition begins before separation. Mean velocity, turbulence, and intermittency profiles are presented.

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