Inverse Fin Arrangement in a Low Pressure Turbine to Improve the Interaction Between Shroud Leakage Flows and Main Flow

2011 ◽  
Author(s):  
Inga Mahle ◽  
Roman Schmierer
Keyword(s):  
Axial Velocity ◽  
Gas Turbines ◽  
Low Pressure ◽  
Flow Path ◽  
Main Flow ◽  
Leakage Flow ◽  
Wall Region ◽  
Leakage Flows ◽  
Low Pressure Turbine ◽  
Mixing Losses

The paper deals with the geometry of the shroud cavities in low pressure gas turbines and presents a design which helps to reduce the losses that arise when the shroud leakage flows interact with the main flow. The fins in low pressure gas turbines are usually attached to the shroud of the blades. They are therefore rotating while the non-rotating honeycomb or abrasive coating is mounted into the casing. The shroud leakage flow, after passing the rear fin, is decelerated in the rear cavity chamber and enters the main flow path with an axial velocity that is smaller than the axial velocity of the main flow. This difference in axial velocity, together with differences in the circumferential velocity, leads to increased turbulence, mixing losses and an unfavorable incidence of the subsequent vane row in the wall region. Contrarily to the usual configuration, the inverse fins in the turbine presented in the paper are attached to the casing while the honeycomb is mounted onto the rotating blades. This arrangement results in the location of the gap between the fin and the honeycomb being very close to the position of re-entry of the leakage flow into the main flow. Therefore, the leakage flow keeps a high velocity resulting from the narrow fin gap until re-entry which reduces the velocity difference with respect to the main flow. Consequently, the mixing losses and subsequent row losses are reduced. Due to the favorable position of the gap and a particular shaping of the honeycomb, the leakage flow is kept close to the surface of the shroud and enters the main flow with little perturbations. The paper presents numerical results of steady 3D simulations of a three-stage low pressure turbine. Results with an ideal flow path (no cavities), with shroud cavities with conventionally rotating fins and with shroud cavities with inverse fins are compared.

Improving the Interaction Between Leakage Flows and Main Flow in a Low Pressure Turbine

2010 ◽  
Author(s):  
Inga Mahle
Keyword(s):  
Pressure Ratio ◽  
Low Pressure ◽  
Flow Path ◽  
Shear Stresses ◽  
Leakage Flow ◽  
Ideal Flow ◽  
Leakage Flows ◽  
Low Pressure Turbine ◽  
The One ◽  
Mixing Losses

A large part of the losses caused by leakage flows through cavities in turbines are mixing losses. They arise when the leakage flow — after passing through the cavity — is re-entering into the mainflow. In the zone of re-entering, the velocity components of the mainflow differ from those of the leakage flow, since the former has passed the precedent airfoil, where it has been accelerated and turned, while the latter has not. This leads to shear stresses which cause increased turbulence and losses. This paper presents a numerical investigation of a device which reduces the mixing losses caused by the leakage flows through inner cavities of a low pressure turbine to 63% of their original value. The device is situated close to the rear openings of the cavities and a large part of the leakage flow is passing through it. The leakage flow is turned and accelerated by the device in a way that brings its velocity components closer to the velocity components of the mainflow. This reduces the mixing losses considerably compared to cavity flows without turning devices. An increase in efficiency of the low pressure turbine of about 0.1% can be noticed. This paper presents numerical results of steady 3D simulations of a three-stage low pressure turbine with a pressure ratio of approximately 3.5. Results with an ideal flow path (no cavities), with inner cavities without turning device and with inner cavities with turning device are compared. Radial distributions of characteristic quantities (turbulent kinetic energy, circumferential velocity etc.) show that these quantities evaluated with cavities with turning device are much closer to the ideal flow path quantities than without. By subtracting the solution with turning device from the one without, the regions where mixing losses are reduced are identified.

scholarly journals The GT24/26 Low Pressure Turbine

1998 ◽  
Author(s):  
Ian K. Jennions ◽  
Thomas Sommer ◽  
Bernhard Weigand ◽  
Manfred Aigner
Keyword(s):  
Gas Turbines ◽  
Low Pressure ◽  
Thermal Design ◽  
Component Technology ◽  
Test Facility ◽  
3D Analysis ◽  
Leakage Flows ◽  
Low Pressure Turbine ◽  
Point Data ◽  
Lp Turbine

The GT24 and GT26 are the latest in a series of gas turbines from ABB. The GT24 is a 60 Hz, 183 MW turbine, while the GT26 is its (scaled) 50 Hz equivalent, producing 265 MW. They feature a 22 stage controlled diffusion aerofoil compressor, two combustors separated by a single stage high pressure turbine with a four stage low pressure (LP) turbine following the second combustor. This arrangement permits very high efficiencies while avoiding high temperatures and the need to use new, expensive materials. The first GT24 was delivered to Jersey Central Power and Light, Gilbert, New Jersey, USA, at the end of 1995 and achieved baseload operation in May 1996. The engine was highly instrumented with some 1200 measurement points to evaluate component performance. Subsequently, a through-flow datamatch to the design point data was made for the LP turbine and is compared to a full 3D multistage analysis in this paper. The 3D analysis accounts for all the cooling and leakage flows that enter the turbine flowpath and maintains a steady flow calculation by means of interface planes between each blade row that remove any circumferential non-uniformity from the computational flow field. To complement this aerodynamic analysis, some heat transfer results from the ABB GT26 test facility in Birr, Switzerland are also shown. The paper demonstrates how component technology for the first stage was verified at four universities and research centers concurrently with the design process. This experimental data supplemented the existing databases and engendered confidence in the overall aero/thermal design approach.

Control of shroud leakage flows to reduce mixing losses in a shrouded axial turbine

2011 ◽  
Vol 226 (5) ◽  
pp. 1263-1277 ◽  
Author(s):  
J Gao ◽  
Q Zheng ◽  
G Yue ◽  
L Sun
Keyword(s):  
Flow Direction ◽  
Flow Simulation ◽  
Main Flow ◽  
Tip Clearance ◽  
Shear Stresses ◽  
Leakage Flow ◽  
Radial Velocity Component ◽  
Axial Turbine ◽  
Leakage Flows ◽  
Mixing Losses

The losses caused by the leakage flows through the rotor tip clearance, and the mixing losses by the re-entering leakage into the main flow are considerable parts of the total losses in turbines. The main reason for the mixing losses is the different velocity components of main and leakage flows. This leads to shear stresses which cause increased turbulence and losses. This article presents a numerical investigation on three different configurations to control the leakage flows: (a) turning vanes are fixed onto the casing between the fins to turn the shroud leakage flow into the main flow direction in order to reduce the circumferential mixing losses; (b) honeycomb bands are inserted into the casing to weaken the leakage flow in the circumferential direction and reduce the circumferential mixing losses due to the special hexagon structure; and (c) downstream edge of the cavity is chamfered to reduce the radial velocity component of the leakage jet and the separation at the downstream edge, and also to reduce the streamwise mixing losses. A 1.5-stage axial turbine with high-aspect ratio blading was used in this study to investigate the sealing designs as mentioned. The flow simulation results of the three configurations were analysed and compared in this article.

Interaction of Wheelspace Coolant and Main Flow in a New Aeroderivative LPT

2006 ◽  
Author(s):  
Francesco Montomoli ◽  
Michela Massini ◽  
Nicola Maceli ◽  
Massimiliano Cirri ◽  
Luca Lombardi ◽  
...  
Keyword(s):  
Flux Distribution ◽  
Low Pressure ◽  
Main Flow ◽  
Space Region ◽  
Heat Flux Distribution ◽  
Gas Generator ◽  
Component Reliability ◽  
Accuracy Requirement ◽  
Low Pressure Turbine ◽  
Hot Gas

Increased computational capabilities make available for the aero/thermal designers new powerful tools to include more geometrical details, improving the accuracy of the simulations, and reducing design costs and time. In the present work, a low-pressure turbine was analyzed, modeling the rotor-stator including the wheel space region. Attention was focused on the interaction between the coolant and the main flow in order to obtain a more detailed understanding of the behavior of the angel wings, to evaluate the wall heat flux distribution, and to prevent hot gas ingestion. Issues of component reliability related to thermal stress require accurate modeling of the turbulence and unsteadiness of the flow field. To satisfy this accuracy requirement, a full 3D URANS simulation was carried out. A reduced count ratio technique was applied in order to decrease numerical simulation costs. The study was carried out to investigate a new two-stage Low Pressure Turbine from GE Infrastructure Oil&Gas to be coupled to a new aeroderivative gas generator, the LM2500+G4, developed by GE Infrastructure, Aviation.

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.

LM9000 Passive Clearance Control (PCC)

2020 ◽  
Author(s):  
Simone Marchetti ◽  
Duccio Nappini ◽  
Roberto De Prosperis ◽  
Paolo Di Sisto
Keyword(s):  
Control System ◽  
Low Pressure ◽  
Industrial Applications ◽  
Flow Path ◽  
Operating Conditions ◽  
Low Pressure Turbine ◽  
Power Turbine ◽  
Extensive Test ◽  
First Time ◽  
Clearance Control

Abstract This paper describes the design of the Free Power Turbine (FPT) of the LM9000, in particularly the design of its Passive Clearance Control (PCC) system. The LM9000 is the aero-derivative version of the GE90-115B jet engine. Its core engine has many common parts with the GE90; what differs is the booster (low pressure compressor) and the lower pressure turbine (LPT). The booster of the LM9000 is without fan because the engine is not used to provide thrust but torque only, subsequently it has a new flow path [5]. The LPT has instead been replaced by an intermediate pressure turbine (IPT) and by the FPT. The IPT drives the booster, while the FPT is a free low-pressure turbine designed for both power generation and mechanical drive industrial applications, including LNG production plants. Due to its different application, the LM9000 FPT flow path differs sensibly from the GE90 LPT, however as the GE90 it is provided of a clearance control system that cools the casing in order to reduce its radial deflection. It is not the first time that a clearance control system has been used in industrial applications; in GE aero-derivative power turbines is already present in the LM6000 and LMS100. Design constraints, system complexity, high environment variability because the PCC is located outside the GT, harsh environments and long periods of usage still make the design of this component challenging. The design of the PCC has been supported by extensive heat transfer and mechanical simulations. Each PCC component has been addressed with a dedicated life calculation and all the blade and seal clearances have been estimated for all the operating conditions of the engine. Simulations have been validated by an extensive test campaign performed on the first engine.

Aerodynamic Effects of an Unshrouded Low Pressure Turbine on a Low Aspect Ratio Exit Guide Vane

2012 ◽  
Author(s):  
Thorsten Selic ◽  
Davide Lengani ◽  
Andreas Marn ◽  
Franz Heitmeir
Keyword(s):  
Aspect Ratio ◽  
Guide Vane ◽  
Low Pressure ◽  
Tip Clearance ◽  
Pressure Probe ◽  
Model Parameters ◽  
Leakage Flow ◽  
Low Pressure Turbine ◽  
Low Aspect Ratio ◽  
The Impact

This paper presents the effects of an unshrouded low pressure turbine (LPT) onto the following exit guide vane row (EGV). The measurement results were obtained in the subsonic test turbine facility at Graz University of Technology by means of a fast response pressure probe in planes downstream of the rotor as well as oil flow visualisation. The test rig was designed in cooperation with MTU Aero Engines and represents the last 1.5 stages of a commercial aero engine. Considerable efforts were put into the adjustment of all relevant model parameters to reproduce the full scale LPT situation. Different tip clearances were evaluated by means of CFD obtained using a commercial Navier-Stokes code and validated with experimental results. The goal is to evaluate the effect of the varying leakage flow on the flow in the low aspect ratio EGV. Special attention is given to the impact on the development of secondary flows as well as the flow structures downstream of the EGV. The effect of the leakage flow causes a change of the flow structure of the EGV, particularly losses. Considering the largest investigated tip-clearance, the losses increased by 71% when compared to a zero-leakage case.

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

2011 ◽  
Author(s):  
Jerrit Da¨hnert ◽  
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 open 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.

Numerical Investigation of the Effect of Tip Leakage Flow on an Aggressive S-Shaped Intermediate Turbine Duct

2009 ◽  
Author(s):  
W. Sanz ◽  
M. Kelterer ◽  
R. Pecnik ◽  
A. Marn ◽  
E. Go¨ttlich
Keyword(s):  
High Pressure ◽  
Low Pressure ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
High Pressure Turbine ◽  
Tip Leakage ◽  
Intermediate Turbine Duct ◽  
Low Pressure Turbine ◽  
High Diffusion ◽  
Gap Height

The demand of a further increased bypass ratio of aero engines will lead to low pressure turbines with larger diameters which rotate at lower speed. Therefore, it is necessary to guide the flow leaving the high pressure turbine to the low pressure turbine at a larger diameter without any loss generating separation or flow disturbances. Due to costs and weight this intermediate turbine duct has to be as short as possible. This leads to an aggressive (high diffusion) S-shaped duct geometry. In order to investigate the influence of the blade tip gap height of a preceding rotor on such a high-diffusion duct flow a detailed measurement campaign in the Transonic Test Turbine Facility at Graz University of Technology has been performed. A high diffusion intermediate duct is arranged downstream a high-pressure turbine stage providing an exit Mach number of about 0.6 and a swirl angle of −15 degrees (counter swirl). A low-pressure vane row is located at the end of the duct and represents the counter rotating low pressure turbine at larger diameter. At the ASME 2007, results of these investigations were presented for two different tip gap heights of 1.5% span (0.8 mm) and 2.4% span (1.3 mm). In order to better understand the flow phenomena observed in the intermediate duct a detailed numerical study is conducted. The unsteady flow through the whole configuration is simulated for both gap heights as well as for a rotor with zero gap height. The unsteady data are compared at the stage exit and inside the duct to study the flow physics. The calculation of the zero gap height configuration allows to determine the influence of the tip leakage flow of the preceding rotor on the intermediate turbine duct. It turns out that for this aggressive duct the tip leakage flow has a very positive effect on the pressure recovery.

Modeling and Analysis of Main Flow–Shroud Leakage Flow Interaction in LP Turbines

2006 ◽  
Author(s):  
Jochen Gier ◽  
Karl Engel ◽  
Bertram Stubert ◽  
Ralf Wittmaack
Keyword(s):  
Main Flow ◽  
Navier Stokes ◽  
Aerodynamic Load ◽  
Leakage Flow ◽  
Modeling And Analysis ◽  
Simplified Approach ◽  
Leakage Flows ◽  
Flow Phenomena ◽  
Flow Effects ◽  
The Impact

Endwall losses significantly contribute to the overall losses in modern turbomachinery, especially when aerodynamic load and pressure ratios are increased. In turbines with shrouded airfoils a large portion of these losses are generated by the leakage flow across the shroud clearance. For the design of modern jet engine turbines it becomes increasingly important to include the impact of shroud leakage flows in the aerodynamic design. There are two main aspects connected to this issue. The first aspect is to optimize the cavity flow and its interaction with the main flow. The second aspect is to perform the airfoil design with boundary conditions, which include the shroud leakage flow effects. In comparison to the simplified approach of neglecting the real endwall geometry and leakage flow this should enable the designer to produce improved airfoils for the entire span. In order to address the second aspect of supporting the airfoil design with improved shroud leakage consideration within the airfoil design process, an efficient procedure for modeling the shroud leakage flow has been implemented into the design Navier-Stokes code. The intention is to model the major leakage flow phenomena without the necessity of pre-defining all details of the shroud geometry. In the paper the results of this model are compared to conventional computations, computations with mesh-resolved cavities and experimental data. The differences are discussed and the impact of certain configuration aspects are analyzed.

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