Numerical Study on the Effects of the Upstream Wake Generator on the Aerodynamic Performance of a High-Lift Low Pressure Turbine Blade

2016 ◽  
Author(s):  
Fabio Bigoni ◽  
Stefano Vagnoli ◽  
Tony Arts ◽  
Tom Verstraete
Keyword(s):  
Turbine Blade ◽  
Numerical Study ◽  
Separation Bubble ◽  
Suction Side ◽  
Low Pressure ◽  
High Lift ◽  
Blade Loading ◽  
Free Stream Turbulence ◽  
Low Pressure Turbine ◽  
Sst Turbulence Model

The aim of the present paper is to analyze and discuss in detail the effects of the upstream incoming wakes on both the aerodynamic loading and the evolution of the laminar separation bubble developing along the suction side of the high-lift T106-C low pressure turbine blade at engine similar Reynolds and Mach numbers, but at a low free stream turbulence level. The investigation is carried out numerically by means of steady and unsteady RANS simulations for two different Reynolds numbers (100,000 and 140,000), employing the SST turbulence model coupled to the γ–Re~θt transition model. The numerical results are compared with the experimental data provided by the von Karman Institute in terms of variation of losses and blade loading between steady and unsteady inflow conditions. In general, the incoming wakes have a crucial effect both on the reduction of the separation bubble and on the modification of the blade loading. This is analyzed in detail, in order to separate these contributions.

Metamodel-Assisted Optimization of a High-Lift Low Pressure Turbine Blade

2017 ◽  
Author(s):  
Fabio Bigoni ◽  
Roberto Maffulli ◽  
Tony Arts ◽  
Tom Verstraete
Keyword(s):  
Turbine Blade ◽  
Separation Bubble ◽  
Differential Evolution Algorithm ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
High Lift ◽  
Laminar Separation ◽  
Low Pressure Turbine ◽  
Kriging Metamodel

The scope of this work is to perform a single-objective optimization of the high-lift and aft-loaded T2 low pressure turbine blade profile previously designed at the von Karman Institute for Fluid Dynamics (VKI). At correct engine Mach and Reynolds numbers and for a uniform inflow at low turbulence level, a laminar separation bubble occurs in the decelerating part of the suction side. The main goal of the optimization is to obtain a high-lift and aft-loaded blade characterized by lower aerodynamic losses with respect to the original profile. The optimization uses a metamodel-assisted Differential Evolution algorithm, with an Ordinary Kriging metamodel performing the low-fidelity evaluations and Numeca FINE/Turbo for the high-fidelity ones. The numerical results relative to the optimized profile are compared with those obtained for the baseline profile, in order to highlight the improvements on the blade aerodynamic performance coming from the optimization process.

Aerodynamic Performance of a Very High Lift Low Pressure Turbine Blade With Emphasis on Separation Prediction

2004 ◽  
Vol 126 (3) ◽  
pp. 406-413 ◽  
Author(s):  
Re´gis Houtermans ◽  
Thomas Coton ◽  
Tony Arts
Keyword(s):  
Turbine Blade ◽  
Separation Bubble ◽  
Separated Flow ◽  
Low Pressure ◽  
Secondary Flows ◽  
Flow Mode ◽  
High Lift ◽  
Flow Angle ◽  
Low Pressure Turbine ◽  
Very High

The present paper is based on an experimental study of a front-loaded very high lift, low pressure turbine blade designed at the VKI. The experiments have been carried out in a low-speed wind tunnel over a wide operating range of incidence and Reynolds number. The aim of the study is to characterize the flow through the cascade in terms of losses, mean outlet flow angle, and secondary flows. At low inlet freestream turbulence intensity, a laminar separation bubble is present, and a prediction model for a separated flow mode of transition has been developed.

Separated Flow Transition in a Low Pressure Turbine Cascade: Mean Flow and Turbulence Spectra

2003 ◽  
Author(s):  
Ralph J. Volino ◽  
Christopher G. Murawski
Keyword(s):  
Boundary Layer ◽  
Free Stream ◽  
Separation Bubble ◽  
Suction Side ◽  
Low Pressure ◽  
Turbine Cascade ◽  
Mean Flow ◽  
Turbulence Spectra ◽  
Free Stream Turbulence ◽  
Low Pressure Turbine

Boundary layer separation, transition and reattachment have been studied experimentally in a low-pressure turbine cascade. Cases with Reynolds numbers (Re) ranging from 50,000 to 200,000 (based on suction surface length and exit velocity) have been considered under low free-stream turbulence conditions. Mean and fluctuating velocity profiles and turbulence spectra are presented for streamwise locations along the suction side of one airfoil and in the wake downstream of the airfoils. Hot film gages on the suction side surface of the airfoil are used to measure the fluctuation level and the spectra of the fluctuations on the surface. Higher Re moves transition upstream. Transition is initiated in the shear layer over the separation bubble and leads to boundary layer reattachment. Peak frequencies in the boundary layer spectra match those found in similar cases in the literature, indicating that the important frequencies may be predictable. Spectra in the wake downstream of the airfoils were similar to the spectra in the boundary layer near the trailing edge of the airfoil. Comparisons to the literature indicate that small but measurable differences in the spectra of the low free-stream turbulence can have a significant effect on boundary layer reattachment.

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.

Wake Control by Boundary Layer Suction Applied to a High-Lift Low-Pressure Turbine Blade

2010 ◽  
Author(s):  
Francesca Satta ◽  
Marina Ubaldi ◽  
Pietro Zunino ◽  
Claudia Schipani
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Turbine Blade ◽  
Suction Side ◽  
Low Pressure ◽  
High Lift ◽  
Velocity Defect ◽  
Boundary Layer Suction ◽  
Low Pressure Turbine ◽  
Rear Part

Wake control by boundary layer suction has been applied to a high-lift low-pressure turbine blade with the intention of reducing the wake velocity defect, hence attenuating wake-blade interaction, and consequently the generation of tonal noise. The experimental investigation has been performed in a large scale linear turbine cascade at midspan. Two Reynolds number conditions (Re = 300000 and Re = 100000), representative of the typical operating conditions of the low pressure aeroengine turbines, have been analyzed. Boundary layer suction has been implemented through a slot placed in the rear part of the profile suction side. The suction rate has been varied in order to investigate its influence on the wake reduction. Mean velocity and Reynolds stress components in the blade to blade plane have been measured by means of a two-component crossed miniature hot-wire. The wake shed from the central blade has been investigated in several traverses in the direction normal to the camber line at the cascade exit. The traverses are located at distances ranging between 5 and 80% of the blade chord from the blade trailing edge. To get an overall estimate of the wake velocity defect reductions obtained by the application of boundary layer suction, the integral parameters of the wake have been also estimated. Moreover, spectra of the velocity fluctuations have been evaluated to get information on the unsteady behaviour of the wake flow when boundary layer suction is applied. The results obtained in the wake controlled by boundary layer suction have been compared with the results in the baseline profile wake at both Reynolds number conditions for the purpose of evaluating the control technique effectiveness. The removal of boundary layer through the slot in the rear part of the profile suction side has been proved to be very effective in reducing the wake shed from the profile. The results show that a reduction greater than 65% of the wake displacement and momentum thicknesses at Re = 300000, and a reduction greater than 75% at Re = 100000 can be achieved by removal of 1.5% and 1.8% of the single passage through flow, respectively.

An Experimental Investigation of the Wake Shed From a High-Lift Low Pressure Turbine Cascade at Different Reynolds Numbers

2008 ◽  
Author(s):  
Francesca Satta ◽  
Marina Ubaldi ◽  
Pietro Zunino ◽  
Claudia Schipani
Keyword(s):  
Boundary Layer ◽  
Experimental Investigation ◽  
Reynolds Number ◽  
Separation Bubble ◽  
Suction Side ◽  
Low Pressure ◽  
Profile Measurement ◽  
High Lift ◽  
Low Pressure Turbine ◽  
Lower Reynolds Number

The paper presents the results of an experimental investigation of the wake shed from a high-lift low-pressure turbine profile. Measurement campaigns have been carried out in a three-blade large-scale turbine linear cascade. The Reynolds number based on the chord length has been varied in the range 100000–500000, to differentiate the influence of the boundary layer separation on the wake development. Two Reynolds number conditions, representative of the typical working conditions of a low pressure aeroengine turbine, have been more extensively investigated. Mean velocity and Reynolds stress components within the wake shed from the central blade have been measured across the wake by means of a two-component crossed miniature hotwire probe. The measuring traverses were located at distances ranging between 2 and 100% of the blade chord from the central blade trailing edge. Moreover, wake integral parameters, at the two Reynolds conditions, have been evaluated and compared. Both velocity and total pressure results show a wider wake occurring at the lower Reynolds number, due to the separation affecting the suction side boundary layer. Furthermore, the momentum thickness has been found to be much higher at the lower Reynolds number, due to the higher losses related to the separation bubble occurring on the blade suction side. The Strouhal number associated with the vortex shedding seems to be influenced by the Reynolds number, due to the different conditions of the suction side boundary layers.

Designing Low-Pressure Turbine Blades With Integrated Flow Control

2005 ◽  
Author(s):  
Jeffrey P. Bons ◽  
Laura C. Hansen ◽  
John P. Clark ◽  
Peter J. Koch ◽  
Rolf Sondergaard
Keyword(s):  
Reynolds Number ◽  
Flow Control ◽  
Turbine Blade ◽  
Separation Bubble ◽  
Low Pressure ◽  
Suction Surface ◽  
Flow Measurements ◽  
Blade Loading ◽  
Low Pressure Turbine ◽  
Wide Range

A low pressure turbine blade was designed to produce a 17% increase in blade loading over an industry-standard airfoil using integrated flow control to prevent separation. The design was accomplished using two-dimensional CFD predictions of blade performance coupled with insight gleaned from recently published work in transition modeling and from previous experiments with flow control using vortex generator jets (VGJs). In order to mitigate the Reynolds number lapse in efficiency associated with LPT airfoils, a mid-loaded blade was selected. Also, separation predictions from the computations were used to guide the placement of control actuators on the blade suction surface. Three blades were fabricated using the new design and installed in a two-passage linear cascade facility. Flow velocity and surface pressure measurements taken without activating the VGJs indicate a large separation bubble centered at 68% axial chord on the suction surface. The size of the separation and its growth with decreasing Reynolds number agree well with CFD predictions. The separation bubble reattaches to the blade over a wide range of inlet Reynolds numbers from 150,000 down to below 20,000. This represents a marked improvement in separation resistance compared to the original blade profile which separates without reattachment below a Reynolds number of 40,000. This enhanced performance is achieved by increasing the blade spacing while simultaneously adjusting the blade shape to make it less aft-loaded but with a higher peak cp. This reduces the severity of the adverse pressure gradient in the uncovered portion of the modified blade passage. With the use of pulsed VGJs, the design blade loading was achieved while providing attached flow over the entire range of Re. Detailed phase-locked flow measurements using three-component PIV show the trajectory of the jet and its interaction with the unsteady separation bubble. Results illustrate the importance of integrating flow control into the turbine blade design process and the potential for enhanced turbine performance.

Transition Mechanisms in Laminar Separated Flow Under Simulated Low Pressure Turbine Aerofoil Conditions

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
Jerrit Dähnert ◽  
Christoph Lyko ◽  
Dieter Peitsch
Keyword(s):  
Reynolds Number ◽  
Separation Bubble ◽  
Separated Flow ◽  
Low Pressure ◽  
Main Flow ◽  
Test Facility ◽  
Flow Conditions ◽  
Laminar Separation ◽  
Free Stream Turbulence ◽  
Low Pressure Turbine

Based on detailed experimental work conducted at a low speed test facility, this paper describes the transition process in the presence of a separation bubble with low Reynolds number, low free-stream turbulence, and steady main flow conditions. A pressure distribution has been created on a long flat plate by means of a contoured wall opposite of the plate, matching the suction side of a modern low-pressure turbine aerofoil. The main flow conditions for four Reynolds numbers, based on suction surface length and nominal exit velocity, were varied from 80,000 to 300,000, which covers the typical range of flight conditions. Velocity profiles and the overall flow field were acquired in the boundary layer at several streamwise locations using hot-wire anemometry. The data given is in the form of contours for velocity, turbulence intensity, and turbulent intermittency. The results highlight the effects of Reynolds number, the mechanisms of separation, transition, and reattachment, which feature laminar separation-long bubble and laminar separation-short bubble modes. For each Reynolds number, the onset of transition, the transition length, and the general characteristics of separated flow are determined. These findings are compared to the measurement results found in the literature. Furthermore, the experimental data is compared with two categories of correlation functions also given in the literature: (1) correlations predicting the onset of transition and (2) correlations predicting the mode of separated flow transition. Moreover, it is shown that the type of instability involved corresponds to the inviscid Kelvin-Helmholtz instability mode at a dominant frequency that is in agreement with the typical ranges occurring in published studies of separated and free-shear layers.

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