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.

Detailed Numerical Characterization of the Suction Side Laminar Separation Bubble for a High-Lift Low Pressure Turbine Blade by Means of RANS and LES

2016 ◽  
Author(s):  
Fabio Bigoni ◽  
Stefano Vagnoli ◽  
Tony Arts ◽  
Tom Verstraete
Keyword(s):  
Large Eddy Simulation ◽  
Separation Bubble ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Laminar Separation Bubble ◽  
High Lift ◽  
Laminar Separation ◽  
Low Pressure Turbine ◽  
Eddy Simulation ◽  
Large Eddy

The scope of this work is to obtain a deep insight of the occurrence, development and evolution of the laminar separation bubble which occurs on the suction side of the high-lift T106-C low pressure turbine blade operated at correct engine Mach and Reynolds numbers. The commercial codes Numeca FINE/Turbo and FINE/Open were used for the numerical investigation of a set of three different Reynolds numbers. Two different CFD approaches, characterized by a progressively increasing level of complexity and detail in the solution, have been employed, starting from a steady state RANS analysis and ending with a Large Eddy Simulation. Particular attention was paid to the study of the open separation occurring at the lowest Reynolds number, for which a Large Eddy Simulation was performed in order to try to correctly capture the involved phenomena and their characteristic frequencies. In addition, the potentialities of the codes employed for the analysis have been assessed.

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.

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.

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.

The Effect of Pulsed Blowing on the Boundary Layer of a Highly Loaded Low Pressure Turbine Blade

2013 ◽  
Author(s):  
Marion Mack ◽  
Roland Brachmanski ◽  
Reinhard Niehuis
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Mach Number ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
Trailing Edge ◽  
Low Pressure Turbine ◽  
Wide Range ◽  
Highly Loaded

The performance of the low pressure turbine (LPT) can vary appreciably, because this component operates under a wide range of Reynolds numbers. At higher Reynolds numbers, mid and aft loaded profiles have the advantage that transition of suction side boundary layer happens further downstream than at front loaded profiles, resulting in lower profile loss. At lower Reynolds numbers, aft loading of the blade can mean that if a suction side separation exists, it may remain open up to the trailing edge. This is especially the case when blade lift is increased via increased pitch to chord ratio. There is a trend in research towards exploring the effect of coupling boundary layer control with highly loaded turbine blades, in order to maximize performance over the full relevant Reynolds number range. In an earlier work, pulsed blowing with fluidic oscillators was shown to be effective in reducing the extent of the separated flow region and to significantly decrease the profile losses caused by separation over a wide range of Reynolds numbers. These experiments were carried out in the High-Speed Cascade Wind Tunnel of the German Federal Armed Forces University Munich, Germany, which allows to capture the effects of pulsed blowing at engine relevant conditions. The assumed control mechanism was the triggering of boundary layer transition by excitation of the Tollmien-Schlichting waves. The current work aims to gain further insight into the effects of pulsed blowing. It investigates the effect of a highly efficient configuration of pulsed blowing at a frequency of 9.5 kHz on the boundary layer at a Reynolds number of 70000 and exit Mach number of 0.6. The boundary layer profiles were measured at five positions between peak Mach number and the trailing edge with hot wire anemometry and pneumatic probes. Experiments were conducted with and without actuation under steady as well as periodically unsteady inflow conditions. The results show the development of the boundary layer and its interaction with incoming wakes. It is shown that pulsed blowing accelerates transition over the separation bubble and drastically reduces the boundary layer thickness.

Exploitation of Subharmonics for Separated Shear Layer Control on a High-Lift Low-Pressure Turbine Using Acoustic Forcing

2013 ◽  
Vol 136 (5) ◽  
Author(s):  
Chiara Bernardini ◽  
Stuart I. Benton ◽  
Jen-Ping Chen ◽  
Jeffrey P. Bons
Keyword(s):  
Shear Layer ◽  
Separation Bubble ◽  
Boundary Layer Separation ◽  
Low Pressure ◽  
Linear Instability ◽  
Laminar Separation ◽  
Significant Control ◽  
Low Pressure Turbine ◽  
Separated Shear Layer ◽  
Sound Control

The mechanism of separation control by sound excitation is investigated on the aft-loaded low-pressure turbine (LPT) blade profile, the L1A, which experiences a large boundary layer separation at low Reynolds numbers. Previous work by the authors has shown that on a laminar separation bubble such as that experienced by the front-loaded L2F profile, sound excitation control has its best performance at the most unstable frequency of the shear layer due to the exploitation of the linear instability mechanism. The different loading distribution on the L1A increases the distance of the separated shear layer from the wall and the exploitation of the same linear mechanism is no longer effective in these conditions. However, significant control authority is found in the range of the first subharmonic of the natural unstable frequency. The amplitude of forced excitation required for significant wake loss reduction is higher than that needed when exploiting linear instability, but unlike the latter case, no threshold amplitude is found. The fluid-dynamics mechanisms under these conditions are investigated by particle image velocimetry (PIV) measurements. Phase-locked PIV data gives insight into the growth and development of structures as they are shed from the shear layer and merge to lock into the excited frequency. Unlike near-wall laminar separation sound control, it is found that when such large separated shear layers occur, sound excitation at subharmonics of the fundamental frequency is still effective with high-Tu levels.

An Experimental Investigation of the Effect of Freestream Turbulence on the Wake of a Separated Low-Pressure Turbine Blade at Low Reynolds Numbers

1999 ◽  
Vol 122 (2) ◽  
pp. 431-433 ◽  
Author(s):  
C. G. Murawski ◽  
K. Vafai
Keyword(s):  
Reynolds Number ◽  
Turbine Blade ◽  
Turbulence Intensity ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
Freestream Turbulence ◽  
Suction Surface ◽  
Low Reynolds Numbers ◽  
Low Pressure Turbine ◽  
Flow Reynolds Number

An experimental study was conducted in a two-dimensional linear cascade, focusing on the suction surface of a low pressure turbine blade. Flow Reynolds numbers, based on exit velocity and suction length, have been varied from 50,000 to 300,000. The freestream turbulence intensity was varied from 1.1 to 8.1 percent. Separation was observed at all test Reynolds numbers. Increasing the flow Reynolds number, without changing freestream turbulence, resulted in a rearward movement of the onset of separation and shrinkage of the separation zone. Increasing the freestream turbulence intensity, without changing Reynolds number, resulted in shrinkage of the separation region on the suction surface. The influences on the blade’s wake from altering freestream turbulence and Reynolds number are also documented. It is shown that width of the wake and velocity defect rise with a decrease in either turbulence level or chord Reynolds number. [S0098-2202(00)00202-9]

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