Mach Number Distribution and Profile Losses for Low-Pressure Turbine Profiles With High Diffusion Factors

2017 ◽  
Vol 139 (10) ◽  
Author(s):  
Roland Brachmanski ◽  
Reinhard Niehuis
Keyword(s):  
Boundary Layer ◽  
Mach Number ◽  
Flow Separation ◽  
Total Pressure ◽  
Suction Side ◽  
Low Pressure ◽  
Pressure Losses ◽  
Low Pressure Turbine ◽  
High Diffusion ◽  
Mach Numbers

The results of this investigation come from two linear cascades at high diffusion factors (DFs). The measurements presented for each low-pressure turbine (LPT) profile were conducted at midspan under a range of Reynolds- and exit Mach numbers. The exit Mach number was varied in a range covering low subsonic up to values where a transonic flow regime on the suction side of the blade could be expected. This work focuses on two profiles with a diffusion factor in a range of 0.18≤DF≤0.22, where values in this range are considered as a comparable for the two cascades. Profile A is a front-loaded design and has shown no obvious flow separation on the suction side of the blade. Compared to the design A, design B is a more aft-loaded profile which exhibits flow separation on the suction side for all Reynolds numbers investigated. The integral total pressure losses were evaluated by wake traverses downstream of the airfoil. To determine the isentropic Mach numbers and the character of the boundary layer along the suction side of the profile, the static pressure measurements and traverses with a flattened Pitot probe were carried out. A correlation between the position of maximum Mach number on the suction side and the integral total pressure losses has been successfully established. The results show that the optimum location of peak Mach number to minimize integral total pressure losses is significantly dependent on the Reynolds number. However, the correlation presented in this paper, which is based on the data of the integral total pressure losses of an attached boundary layer, is not able to predict the integral total pressure loss or the location of the maximum Mach number on the suction side of the blade when an open separation bubble occurs.

About the Distribution of the Mach Number and Losses Under Consideration of the Diffusion Factor: Profile Distribution and Losses for Low Pressure Turbine Profiles With High Diffusion Factors Under Steady Flow Conditions

2016 ◽  
Author(s):  
Roland Brachmanski ◽  
Reinhard Niehuis
Keyword(s):  
Boundary Layer ◽  
Mach Number ◽  
Turbulence Intensity ◽  
Flow Separation ◽  
Total Pressure ◽  
Suction Side ◽  
Diffusion Factor ◽  
Pressure Losses ◽  
Low Pressure Turbine ◽  
Exit Mach Number

The results of this investigation consist of two linear cascades at high diffusion factors. The present measurements for each low pressure turbine profile were conducted at midspan under a range of Reynolds- and exit Mach numbers. The exit Mach number was varied in a range covering low subsonic up to values where a transonic flow regime on the suction side of the blade could be expected. The variation of the exit Mach number was also used to create different locations of the maximum Mach number and to evaluate the resulting total pressure losses. This work focuses on two profiles with a diffusion factor in a range of 0.18 ≤ DF ≤ 0.22, which is considered as a comparable level for the two cascades. The profile A is a front-loaded design and has shown no obvious flow separation on the suction side of the blade. Compared to the profile A the design B is a more aft-loaded profile which indicates flow separation on the suction side for all investigated Reynolds numbers. The integral total pressure losses were evaluated by wake traverses downstream of the profile. To determine the isentropic Mach numbers and the character of the boundary layer along the suction side of the profile, static pressure tappings and measurements with a flattened Pitot probe were carried out. Numerical studies were also conducted to investigate further the influence of a reduced turbulence intensity on the boundary layer of the suction side of design B. The results show that the optimum of the integral total pressure losses are significantly dependent on the Reynolds number. Therefore a correlation between the maximum Mach number on the suction side and the integral total pressure losses has been successfully established. A significant change of the turbulence intensity at the inlet of the cascade leads to shift of the location of the maximum Mach number. It also results in an equivalent change of the total pressure losses, which has been predicted by the trend line. However, the trend lines, which are based on the data of the integral total pressure losses of an attached boundary layer, are not able to predict the integral total pressure loss or the location of the maximum Mach number on the suction side of the blade since an open separation bubble occurs.

A Comparison of Three Low Pressure Turbine Designs

2013 ◽  
Vol 135 (5) ◽  
Author(s):  
Christian T. Wakelam ◽  
Martin Hoeger ◽  
Reinhard Niehuis
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Total Pressure ◽  
Maximum Velocity ◽  
Suction Side ◽  
Low Pressure ◽  
Surface Boundary ◽  
Suction Surface ◽  
Pressure Losses ◽  
Low Pressure Turbine

As part of the current research, three low pressure turbine (LPT) geometries—which were designed with a common pitch, axial chord, inlet angle, and exit Mach number and to create the same nominal level of turning—are compared. Each of the LPT cascades was investigated under a range of Reynolds numbers, exit Mach numbers, and under the influence of a moving bar wake generator. Profile static pressure distributions, wake traverses at 5% and 40% axial chord downstream of the trailing edge, and suction side boundary layer traverses were used to compare the performance of the three designs. The total pressure losses are strongly dependent on both the maximum velocity location as well as the diffusion on the suction surface. The importance of the behavior of the pressure surface boundary layer turned out to be negligible in comparison. Cases with equivalent operating Reynolds number and suction side diffusion level are compared in terms of the total pressure losses that are generated. It is shown that a relationship between loss and suction side maximum velocity location exists. An optimum suction side maximum velocity location depends on the Reynolds number, diffusion factor, and wake passing frequency.

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.

Investigation of Variated Unsteady Inflow Boundary Conditions on the Transition Behavior of a Low Pressure Turbine Cascade Family

2014 ◽  
Author(s):  
Franz F. Blaim ◽  
Roland E. Brachmanski ◽  
Reinhard Niehuis
Keyword(s):  
Boundary Condition ◽  
Transport Equation ◽  
Flow Separation ◽  
Total Pressure ◽  
Low Pressure ◽  
Test Facility ◽  
Number Range ◽  
Pressure Losses ◽  
Low Pressure Turbine ◽  
Transition Behavior

The objective of this paper is to analyze the influence of incoming periodic wakes, considering the variable width, on the integral total pressure loss for two low pressure turbine (LPT) airfoils. In order to reduce the overall weight of a LPT, the pitch to chord ratio was continuously increased, during the past decades. However, this increase encourages the development of the transition phenomena or even flow separation on the suction side of the blade. At low Reynolds numbers, large separation bubbles can occur there, which are linked with high total pressure losses. The incoming wakes of the upstream blades are known to trigger early transition, leading to a reduced risk of flow separation and hence minor integral total pressure losses caused by separation. For the further investigation of these effects, different widths of the incoming wakes will be examined in detail, here. This variation is carried out by using the numerical Unsteady Reynolds Averaged Solver TRACE developed by the DLR Cologne in collaboration with MTU Aero Engines AG. For the variation of the width of the wakes, a variable boundary condition was modeled, which includes the wake vorticity parameters. The width of the incoming wakes was used as the relevant variable parameter. The implemented boundary condition models the unsteady behavior of the incoming wakes by the variation of the velocity profile, using a prescribed frequenc. TRACE can use two different transition models; the main focus here is set to the γ–Reθt transition model, which uses local variables in a transport equation, to trigger the transition within the turbulence transport equation system. The experimental results were conducted at the high speed cascade open loop test facility at the Institute for Jet Propulsion at the University of the German Federal Armed Forces in Munich. For the investigation presented here, two LPT profiles — which were designed with a similar inlet angle, turning, and pitch are analyzed. However, with a common exit Mach number and a similar Reynolds number range between 40k and 400k, one profile is front loaded and the other one is aft loaded. Numerical unsteady results are in good agreement with the conducted measurements. The influence of the width of the wake on the time resolved transition behavior, represented by friction coefficient plots and momentum loss thickness will be analyzed in this paper.

Recognition of Structures Leading to Transition in a Low Pressure Turbine Cascade: Effect of Reduced Frequency

2019 ◽  
Author(s):  
D. Lengani ◽  
D. Simoni ◽  
M. Ubaldi ◽  
P. Zunino ◽  
F. Bertini
Keyword(s):  
Boundary Layer ◽  
Suction Side ◽  
Low Pressure ◽  
Turbine Cascade ◽  
Turbulent Structures ◽  
Time Resolved ◽  
Low Pressure Turbine ◽  
Reduced Frequency ◽  
Displacement Thickness ◽  
Wake Passing

Abstract The boundary layer developing over the suction side of a low pressure turbine cascade operating under unsteady inflow conditions has been experimentally investigated. Time-resolved Particle Image Velocimetry (PIV) measurements have been performed in two orthogonal planes, the blade to blade and a wall parallel plane embedded within the boundary layer, for two different wake reduced frequencies. Proper Orthogonal Decomposition (POD) has been used to analyze the data and to provide an interpretation of the most significant flow structures for each phase of the wake passing cycle. To this purpose, a POD based procedure that sorts the data synchronizing the measurements of the two planes has been developed. Phase averaged data are then obtained for both cases. Moreover, once properly sorted, POD has been applied to sub-ensembles of data at the same relative phase within the wake passing cycle. Detailed information on the most energetic turbulent structures at a particular phase are obtained with this procedure (called phased POD), overcoming the limit of classical phase average that just provides a statistical representation of the turbulence field. Furthermore, the synchronization of the measurements in the two planes allows the computation of the characteristic dimension of boundary layer structures that are responsible for transition. These structures are often identified as vortical filaments parallel to the wall, typically referred to as boundary layer streaks. The largest and most energetic structures are observed when the wake centerline passes over the rear part of the suction side, and they appear practically the same for both reduced frequencies. The passing wake forces transition leading to the breakdown of the boundary layer streaks. Otherwise, the largest differences between the low and high reduced frequency are observed in the calmed region. The post-processing of these two planes further allowed us to compute the spacing of the streaks and make it non-dimensional by the boundary layer displacement thickness observed for each phase. The non-dimensional value of the streaks spacing is about constant, irrespective of the reduced frequency.

Study of Flow Controlling on LP Turbine at Different Reynolds Number

2012 ◽  
Author(s):  
Muhammad Aqib Chishty ◽  
Hossein Raza Hamdani ◽  
Khalid Parvez ◽  
Muhammad Nafees Mumtaz Qadri
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Flow Separation ◽  
Separation Bubble ◽  
Low Pressure ◽  
Control Flow ◽  
Loss Coefficient ◽  
Shear Stresses ◽  
Low Pressure Turbine ◽  
Lp Turbine

Active and passive techniques have been used in the past, to control flow separation. Numerous studies were published on controlling and delaying the flow separation on low pressure turbine. In this study, a single dimple (i.e. passive device) is engraved on the suction side of LP turbine cascade T106A. The main aim of this research is to find out the optimum parameters of dimple i.e. diameter (D) and depth (h) which can produce strong enough vortex that can control the flow either in transition or fully turbulent phase. Furthermore, this optimal dimple is engraved to suppress the boundary layer separation at different Reynolds number (based on the chord length and inlet velocity). The dimple of different depth and diameter are used to find the optimal depth to diameter ratio. Computational results show that the optimal ratio of depth to diameter (h/D) for dimple is 0.0845 and depth to grid boundary layer (h/δ) is 0.5152. This optimized dimple efficiently reduces the normalized loss coefficient and it is found that the negative values of shear stresses found in uncontrolled case are being removed by the dimple. After that, dimple of optimized parameters are used to suppress the laminar separation bubble at different Re∼25000, 50000 and 91000. It was noticed that the dimple did not reduce the losses at Re∼25000. But at Re∼50000, it produced such a strong vortex that reduced the normalized loss coefficient to 25%, while 5% losses were reduced at Re∼91000. It can be concluded that the optimized dimple effectively controlled flow separation and reduced normalized loss coefficient from Re 25000 to 91000. As the losses are decreased, this will increase the low pressure turbine efficiency and reduce its fuel consumption.

The Influence of Reynolds Number, Mach Number and Incidence Effects on Loss Production in Low Pressure Turbine Airfoils

2006 ◽  
Author(s):  
Rau´l Va´zquez ◽  
Antonio Antoranz ◽  
David Cadrecha ◽  
Leyre Arman˜anzas
Keyword(s):  
Reynolds Number ◽  
Mach Number ◽  
Low Pressure ◽  
Low Pressure Turbine ◽  
Wide Range ◽  
Flow Features ◽  
Mach Numbers ◽  
Turbine Airfoils ◽  
Annular Cascade ◽  
The Impact

This paper presents an experimental study of the flow field in an annular cascade of Low Pressure Turbine airfoils. The influence of Reynolds number, Mach number and incidence on profile and end wall losses have been investigated. The annular cascade consisted of 100 high lift, high aspect ratio, high turning blades that are characteristic of modern LP Turbines. The investigation was carried out for a wide range of Reynolds numbers, extending from 120k to 315k, exit Mach numbers, from 0.5 to 0.9, and incidences from −20 to +14 degrees. Results clearly indicate a significant effect of incidence and Mach number in secondary loss production; however, the Reynolds number shows it much weaker impact. It has also been found that the profile loss production is strongly influenced by both Reynolds and Mach numbers, being the impact of the incidence weaker. Finally, measured data suggest that, in order to properly reproduce the performance of these types of airfoils, annular cascades can be required as far as linear cascades may miss some essential flow features.

scholarly journals Reynolds, Mach and free-stream turbulence effects on the flow in a low-pressure turbine

2021 ◽  
pp. 1-17
Author(s):  
Maxime Fiore ◽  
Nicolas Gourdain
Keyword(s):  
Reynolds Number ◽  
Mach Number ◽  
Free Stream ◽  
Guide Vane ◽  
Flow Behavior ◽  
Suction Side ◽  
Boundary Layer Separation ◽  
Low Pressure ◽  
Free Stream Turbulence ◽  
Low Pressure Turbine

Abstract This paper presents the Large Eddy Simulation of a Low-Pressure Turbine Nozzle Guide Vane for different Reynolds (Re) and Mach numbers (Ma) with or without inlet turbulence prescribed. The analysis is based on a slice of a LPT blading representative of a midspan flow. The characteristic Re of the LPT can vary by a factor of four between take-off and cruise conditions. In addition, the LPT operates at different Ma and the incident flow can have significant levels of turbulence due to upstream blade wakes. The paper investigates numerically using LES the flow around a LPT blading with three different Reynolds number Re = 175'000 (cruise), 280'000 (mid-level altitude) and 500'000 (take-off) keeping the same characteristic Mach number Ma = 0.2 and three different Mach number Ma = 0.2, 0.5 and 0.8 keeping the same Reynolds number Re= 280'000. These different simulations are performed with 0% Free Stream Turbulence (FST) followed by inlet turbulence (6% FST). The study focuses on different flow characteristics: pressure distribution around the blade, near-wall flow behavior, loss generation and Turbulent Kinetic Energy budget. The results show an earlier boundary layer separation on the aft of the blade suction side when the Re is increased while the free-stream turbulence delays separation. The TKE budget shows the predominant effect of the turbulent production and diffusion in the wake, the axial evolution of these different terms being relatively insensitive to Re and Ma.

Transition Modelling for Vortex Generating Jets on Low-Pressure Turbine Profiles

2011 ◽  
Author(s):  
Florian Herbst ◽  
Dragan Kozˇulovic´ ◽  
Joerg R. Seume
Keyword(s):  
Total Pressure ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
Quantitative Prediction ◽  
Design Parameters ◽  
Transition Model ◽  
Pressure Losses ◽  
Low Pressure Turbine ◽  
Wide Range ◽  
Local Transition

Steady blowing vortex generating jets (VGJ) on highly-loaded low-pressure turbine profiles have shown to be a promising way to decrease total pressure losses at low Reynolds-numbers by reducing laminar separation. In the present paper, the state of the art turbomachinery design code TRACE with RANS turbulence closure and coupled γ-ReΘ transition model is applied to the prediction of typical aerodynamic design parameters of various VGJ configurations in steady simulations. High-speed cascade wind tunnel experiments for a wide range of Reynolds-numbers, two VGJ positions, and three jet blowing ratios are used for validation. Since the original transition model overpredicts separation and losses at Re2is ≤ 100·103 an extra mode for VGJ induced transition is introduced. Whereas the criterion for transition is modelled by a filtered Q vortex criterion the transition development itself is modelled by a reduction of the local transition-onset momentum-thickness Reynolds number. The new model significantly improves the quality of the computational results by capturing the corresponding local transition process in a physically reasonable way. This is shown to yield an improved quantitative prediction of surface pressure distributions and total pressure losses.

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