scholarly journals The Impact of Combustor Turbulence on Turbine Loss Mechanisms

2020 ◽  
Vol 142 (9) ◽  
Author(s):  
Masha Folk ◽  
Robert J. Miller ◽  
John D. Coull
Keyword(s):  
Boundary Layer ◽  
Impinging Jets ◽  
Deep Penetration ◽  
Turbine Cascade ◽  
Turbulent Length Scale ◽  
Blade Row ◽  
High Turbulence ◽  
The Impact ◽  
Profile Loss ◽  
Loss Mechanisms

Abstract A blade row that is located downstream of a combustor has an extremely high turbulence intensity at the inlet, typically above 10%. The peak turbulent length scale is also high, at around 20% of the chord of the downstream blade row. In a combustor, the turbulence is created by impinging jets in crossflow. This may result in the turbulence being anisotropic in nature. The aim of this paper is to investigate the effect of combustor turbulence on the loss mechanisms which occur in a turbine blade row. The paper has a number of important findings. The combustor turbulence is characterized and is shown to be isotropic in nature. It shows that, when no pressure gradient is present, combustor turbulence increases the loss of a turbulent boundary layer by 22%. The mechanism responsible for this change is shown to be a deep penetration of the turbulence into the boundary layer. It shows that the presence of combustor turbulence increases the profile loss and endwall loss in the turbine cascade studied by 37% and 47%, respectively. The presence of combustor turbulence also introduces a freestream loss resulting in the total loss of the turbine cascade rising by 47%. When these loss mechanisms were applied to the vane alone, of an engine representative high-pressure turbine, it was found to result in a 1.3% reduction in stage efficiency.

scholarly journals The Impact of Combustor Turbulence on Turbine Loss Mechanisms

2019 ◽  
Author(s):  
Masha Folk ◽  
Robert J. Miller ◽  
John D. Coull
Keyword(s):  
Boundary Layer ◽  
Cross Flow ◽  
Impinging Jets ◽  
Deep Penetration ◽  
Turbine Cascade ◽  
Turbulent Length Scale ◽  
Blade Row ◽  
High Turbulence ◽  
The Impact ◽  
Loss Mechanisms

Abstract A blade row which is located downstream of a combustor has an extremely high turbulence intensity at inlet, typically above 10%. The peak turbulent length scale is also high, at around 20% of the chord of the downstream blade row. In a combustor, the turbulence is created by impinging jets in cross flow. This may result in the turbulence being anisotropic in nature. The aim of this paper is to investigate the effect of combustor turbulence on the loss mechanisms which occur in a turbine blade row. The paper has a number of important findings. The combustor turbulence is characterized and is shown to be isotropic in nature. It shows that, when no pressure gradient is present, combustor turbulence increases the loss of a turbulent boundary layer by 22%. The mechanism responsible for this change is shown to be a deep penetration of the turbulence into the boundary layer. It shows that the presence of combustor turbulence increases the profile loss and endwall loss in the turbine cascade studied by 37% and 47%, respectively. The presence of combustor turbulence also introduces a freestream loss resulting in the total loss of the turbine cascade rising by 47%. When these loss mechanisms were applied to the vane alone, of an engine representative high pressure turbine, it was found to result in a 1.3% reduction in stage efficiency.

A Numerical Investigation Into the Sources of Endwall Loss in Axial Flow Turbines

2012 ◽  
Author(s):  
John Denton ◽  
Graham Pullan
Keyword(s):  
Boundary Layer ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Axial Flow ◽  
Turbine Cascade ◽  
Plane Model ◽  
Blade Row ◽  
Axial Turbines ◽  
Different Sources ◽  
Good Agreement

Endwall loss, often termed “secondary loss”, in axial turbines has been intensively studied for many years, despite this the physical origin of much of the loss is not really understood. This lack of understanding is a serious impediment to our ability to predict the loss and to the development of methods for reducing it. This paper aims to study the origins of the loss by interrogating the results from detailed and validated CFD calculations. The calculation method is first validated by comparing its predictions to detailed measurements in a turbine cascade. Very good agreement between the calculations and the measurements is obtained. The solution is then examined in detail to highlight the sources of entropy generation in the cascade, several different sources of loss are found to be significant. The same blade row is then used to study the effects of the of the inlet boundary layer thickness on the loss. It is found that only the inlet boundary layer loss and the mixing loss vary greatly with inlet boundary layer thickness. Finally a complete 50% reaction stage, with identical stator and rotor blade profiles, is examined using both steady calculations, with a mixing plane model, and the time average of unsteady calculations. It is found that the endwall flow in the rotor is completely different from that in the stator. Because of this it is considered that results from endwall flow and loss measurements in cascades are of limited relevance to the endwall flow in a real turbine. The results are also used to discuss the validity of the mixing plane model.

A Methodology for a Detailed Loss Prediction in Low Pressure Steam Turbines

2017 ◽  
Author(s):  
Marius Grübel ◽  
Robin M. Dovik ◽  
Markus Schatz ◽  
Damian M. Vogt
Keyword(s):  
Boundary Layer ◽  
Evaluation Method ◽  
Three Dimensional ◽  
Low Pressure ◽  
Steam Turbines ◽  
Cfd Simulations ◽  
Depth Analysis ◽  
Pressure Steam ◽  
The Impact ◽  
Loss Mechanisms

An evaluation method for CFD simulations is presented, which allows an in-depth analysis of different loss mechanisms applying the approach of entropy creation proposed by Denton. The entropy creation within each single mesh element is determined based on the entropy flux through the cell faces and therefore the locations, where losses occur, can be identified clearly. By using unique features of the different loss mechanisms present in low pressure steam turbines, the losses are categorized into boundary layer, wake mixing and shock losses as well as thermodynamic wetness losses. The suitability of the evaluation method is demonstrated by means of steady state CFD simulations of the flow through a generic last stage of a low pressure steam turbine. The simulations have been performed on streamtubes extracted from three-dimensional simulations representing the flow at 10 % span. The impact of non-equilibrium steam effects on the overall loss composition of the stator passage is investigated by comparing the results to an equilibrium steam simulation. It is shown, that the boundary layer losses for the investigated case are of similar magnitude, but the shock and wake losses exhibit significant differences.

On the Impact of Geometric Variability on Fan Aerodynamic Performance, Unsteady Blade Row Interaction, and Its Mechanical Characteristics

2014 ◽  
Vol 136 (9) ◽  
Author(s):  
R. Schnell ◽  
T. Lengyel-Kampmann ◽  
E. Nicke
Keyword(s):  
Boundary Layer ◽  
Standard Deviation ◽  
Mechanical Characteristics ◽  
Principal Component ◽  
Aerodynamic Performance ◽  
Pressure Amplitude ◽  
Turbulent Transition ◽  
Blade Row ◽  
The Impact ◽  
Blade Row Interaction

The focus of the present study is to assess and quantify the uncertainty in predicting the steady and unsteady aerodynamic performance as well as the major mechanical characteristics of a contrarotating turbofan, primarily due to geometric variations stemming from the manufacturing process. The basis of this study is the optically scanned blisk of the first rotor, for which geometric variations from blade to blade are considered. In a first step, selected profile sections of the first rotor were evaluated aerodynamically by applying the 2D coupled Euler/boundary-layer solver mises. Statistical properties of the relevant flow quantities were calculated firstly based on the results of the nine manufactured blades. In a second step, the geometric variations were decomposed into their corresponding eigenforms by means of principal component analysis (PCA). These modes were the basis for carrying out Monte Carlo (MC) simulations in order to analyze in detail the blade's aerodynamic response to the prescribed geometric variations. By means of 3D-computational fluid dynamics (CFD) simulations of the entire fan stage for all the nine scanned rotor 1 blade geometries, the variation of the overall stage performance parameters will be quantified. The impact of the instrumentation will be discussed, here partly doubling the standard deviation of the major performance indicators for the instrumented blades and also triggering a premature laminar/turbulent transition of the boundary layer. In terms of the unsteady blade row interaction, the standard deviation of the resulting blade pressure amplitude shall be discussed based on unsteady simulations, taking advantage of a novel harmonic balance approach. It will be shown that the major uncertainty in terms of the predicted blade pressure amplitude is in the aft part of the front rotor and results from upstream shock/blade interaction. Apart from the aerodynamic performance, an analysis of the mechanical properties in terms of Campbell characteristics and eigenfrequencies was carried out for each of the scanned blades of rotor 1, reflecting the frequency scattering of each eigenmode due to geometric variability.

Effects of Upstream Platform Geometry on the Endwall Flows of a Turbine Cascade

2005 ◽  
Author(s):  
Elena de la Rosa Blanco ◽  
H. P. Hodson ◽  
R. Va´zquez
Keyword(s):  
Boundary Layer ◽  
Separation Bubble ◽  
Turbine Cascade ◽  
Blade Profile ◽  
Linear Cascade ◽  
Surface Separation ◽  
Pressure Surface ◽  
Low Pressure Turbine ◽  
Large Pressure ◽  
Blade Row

This paper describes the effect that the endwall geometry has on the endwall flows in the vicinity of the blade platform in a low-pressure turbine. The aim of this work is to assess the effect on blade performance of a step in hub diameter just ahead of the blade row. The blade profile under consideration is of high aspect ratio and characterized by a large pressure surface separation bubble. The tests are conducted on a linear cascade and the experimental results are supported by numerical simulations. Two different steps are employed, i.e., forward facing and backward facing steps. Furthermore, the size of the step and the thickness of the inlet endwall boundary layer are also varied. It was found that the presence of the step ahead of the blade row can significantly alter the structure and the strength of the endwall flows. A backward facing step gives rise to lower losses when compared with a flat endwall. However, the effect is found to be dependent on the step height and the thickness of the approaching boundary layer. A forward facing step, on the other hand, produces higher losses than a flat endwall.

The Influence of Multimode Transition Initiated by Periodic Wakes on the Profile Loss of a Linear Compressor Cascade

2000 ◽  
Author(s):  
Reinhold Teusch ◽  
Stefan Brunner ◽  
Leonhard Fottner ◽  
Marius Swoboda
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Separation Bubble ◽  
Compressor Cascade ◽  
Linear Compressor ◽  
Laminar Separation ◽  
Blade Row ◽  
Linear Compressor Cascade ◽  
Profile Loss ◽  
Undisturbed Flow

This paper presents results of boundary layer and loss measurements in a high speed cascade wind tunnel on a linear compressor cascade under the influence of unsteady, periodic wakes. The wakes of an upstream blade row were simulated by cylindrical bars moved by a belt mechanism upstream of the cascade. Extensive hot-film array, hot-wire and pressure measurements with variation of steady and unsteady inlet flow conditions have been performed for a better understanding of the transition and loss mechanisms on a blade row interacting with wakes. The incoming wakes are inducing early forced transition in the boundary layer followed in time by calmed regions. Due to its higher shear stress level and its fuller velocity profile, the calmed flow is able to suppress laminar separation bubbles and to delay transition in the region with undisturbed flow between wakes, playing a significant role in the loss generation process. At the investigated low Reynolds number, where the measurements for the steady flow case showed a well-developed laminar separation bubble, reductions of profile loss up to 20% were observed for the measured configuration. In the case of the high Reynolds number, where in undisturbed flow only a small separation bubble was detected, a profile loss rise up to 30% was measured. Beside a better understanding of unsteady flow physics the goal of these basic investigations of unsteady transition is to create a wide database for the improvement of transition modeling in unsteady CFD codes.

Investigation of Low Solidity LP Turbine Cascade With Flow Control: Part 1—Active Flow Control Using Jet-Flap

2010 ◽  
Author(s):  
Ping-Ping Chen ◽  
Wei-Yang Qiao ◽  
Hua-Ling Luo ◽  
Farhan Ali Hashmi
Keyword(s):  
Boundary Layer ◽  
Flow Control ◽  
Boundary Layer Separation ◽  
Turbine Cascade ◽  
Suction Surface ◽  
Layer Separation ◽  
Turbine Cascades ◽  
Lp Turbine ◽  
The Impact ◽  
Highly Loaded

Increasing the airfoil lift and decreasing the solidity of turbine cascade are the effective ways to decrease blade count which lead to the reduction of weight and hardware cost of gas turbine in aircraft engine. The challenge with this effort is to prevent the flow separation on blade suction surface and to keep the efficiency at high levels. Recent investigations on the blade-flap have demonstrated dramatic reduction in the separation losses of turbine. It would be very attractive to integrate the blade-flap in the design of enhanced loaded turbine. The critical science that will enable this design innovation is a comprehensive understanding of the effect of flow control device on the boundary layer separation. The purpose of the present work was to investigate the impact of turbine cascade solidity on loss mechanisms (airfoil lift level) and to study the feasibility to develop low solidity and highly loaded LP turbine cascade blade using blade flap. This paper is the Part I of the study concerned with performance improvement of low solidity and highly loaded LP turbine cascade blade with jet-flap. The Part II is concerned with the Gurney-flap. Investigation on three turbine cascades with same type of airfoil but different solidity is presented in this paper. These turbine cascades are all constructed with the P&W LPTs highly loaded airfoil Pack B. Two dimensional steady Reynolds-averaged Navier-Stokes equations are solved for the flow of these cascades. It is shown that appropriate jet flap could decrease turbine cascade solidity about 12.5% without the considerable increase in loss, the flow deflection of the turbine cascade mainstream can be increased by jet-flap, and then contribute to increased blade loading. Because of the augmented deflection of the cascade mainstream, the flow velocity at suction side of the adjacent blade increases. This results in extension of the flow accelerating region and reduction of flow diffusion on the blade suction surface, consequently there is a delay in the boundary layer separation and/or makes the reattachment point advanced. In fact, the neighboring blade boundary layer flow is affected by the deflection of the mainstream, not on the flow of local boundary directly.

scholarly journals The impact of a foehn wind on PM10 concentrations and the urban boundary layer in complex terrain: a case study from Kraków, Poland

Tellus B ◽  
2021 ◽  
Vol 73 (1) ◽  
pp. 1-26
Author(s):  
Piotr Sekuła ◽  
Anita Bokwa ◽  
Zbigniew Ustrnul ◽  
Mirosław Zimnoch ◽  
Bogdan Bochenek
Keyword(s):  
Boundary Layer ◽  
Complex Terrain ◽  
Urban Boundary Layer ◽  
The Impact

Experimental study of heat transfer in the boundary layer of a flat plate with the impact of weak shock waves on the leading edge

2020 ◽  
Author(s):  
V. L. Kocharin ◽  
A. A. Yatskikh ◽  
D. S. Prishchepova ◽  
A. V. Panina ◽  
Yu. G. Yermolaev ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Experimental Study ◽  
Shock Waves ◽  
Flat Plate ◽  
Leading Edge ◽  
Weak Shock ◽  
The Impact

scholarly journals Technical note: Boundary layer height determination from Lidar for improving air pollution episode modelling: development of new algorithm and evaluation

2017 ◽  
Author(s):  
Ting Yang ◽  
Zifa Wang ◽  
Wei Zhang ◽  
Alex Gbaguidi ◽  
Nubuo Sugimoto ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Air Pollution ◽  
High Performance ◽  
Accurate Determination ◽  
Technical Note ◽  
Strong Increase ◽  
Layer Height ◽  
Boundary Layer Height ◽  
Retrieval Algorithms ◽  
The Impact

Abstract. Predicting air pollution events in low atmosphere over megacities requires thorough understanding of the tropospheric dynamic and chemical processes, involving notably, continuous and accurate determination of the boundary layer height (BLH). Through intensive observations experimented over Beijing (China), and an exhaustive evaluation existing algorithms applied to the BLH determination, persistent critical limitations are noticed, in particular over polluted episodes. Basically, under weak thermal convection with high aerosol loading, none of the retrieval algorithms is able to fully capture the diurnal cycle of the BLH due to pollutant insufficient vertical mixing in the boundary layer associated with the impact of gravity waves on the tropospheric structure. Subsequently, a new approach based on gravity wave theory (the cubic root gradient method: CRGM), is developed to overcome such weakness and accurately reproduce the fluctuations of the BLH under various atmospheric pollution conditions. Comprehensive evaluation of CRGM highlights its high performance in determining BLH from Lidar. In comparison with the existing retrieval algorithms, the CRGM potentially reduces related computational uncertainties and errors from BLH determination (strong increase of correlation coefficient from 0.44 to 0.91 and significant decrease of the root mean square error from 643 m to 142 m). Such newly developed technique is undoubtedly expected to contribute to improve the accuracy of air quality modelling and forecasting systems.

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