Effect of Purge Flow Swirl on Hot Gas Ingestion Into Turbine Rim Cavities

2013 ◽  
Author(s):  
M. B. Zlatinov ◽  
C. S. Tan ◽  
D. Little ◽  
M. Montgomery
Keyword(s):  
Mass Flow ◽  
Flow Model ◽  
External Pressure ◽  
Physical Principle ◽  
Design Parameters ◽  
Air Mass ◽  
Hot Gas ◽  
Flow Swirl ◽  
Purge Flow ◽  
Axial Turbines

Purge air, injected through seals in the hub of axial turbines, is necessary to prevent hot gas ingestion into endwall cavities, but generates losses by viscous interaction with the mainstream flow. Recent work has shown that for a given purge air mass flow rate, introducing swirl into the purge flow can reduce these losses. This paper investigates the effect of introducing such swirl on the ability of purge flow to prevent ingestion. In particular, it is observed that in the presence of the rotating external pressure non-uniformity due to a downstream blade row, swirled purge flow is much less effective in sealing a turbine disk rim cavity compared to non-swirled purge flow. This is reflected in higher purge air mass flow rates necessary to seal a given cavity, and that in turn diminishes the positive effect of pre-swirling purge flow in the first place. It is shown that this will occur whenever the circumferential pressure disturbance associated with the downstream rotating blades is the dominant driver for externally induced ingestion. It is reasoned that swirled purge flow moves with the rotating pressure non-uniformity and responds to it more readily than non-swirled purge flow, which sees the averaged effect of multiple blade passing events. A flow model based on this physical principle is developed, showing good agreement with computational results. The model yields an ingestion criterion with a parametric dependence on purge flow design parameters. The analysis is extended to an unsteady situation, whereby the effects of both stationary and rotating pressure non-uniformities, from vanes and blades respectively, are taken into account simultaneously. This unsteady flow model points to an optimal design space, in the context of minimizing purge flow losses while maintaining an appropriate margin with regard to hot gas ingestion.

Investigation of Flow Instabilities Near the Rim Cavity of a 1.5 Stage Gas Turbine

2009 ◽  
Author(s):  
M. Rabs ◽  
F.-K. Benra ◽  
H. J. Dohmen ◽  
O. Schneider
Keyword(s):  
Gas Turbine ◽  
Mass Flow ◽  
Gas Turbines ◽  
Flow Instabilities ◽  
Navier Stokes ◽  
Flow Rates ◽  
Air Mass ◽  
Hot Gas ◽  
Path Modelling ◽  
Mass Flow Rates

The present paper gives a contribution to a better understanding of the flow at the rim and in the wheel space of gas turbines. Steady state and time-accurate numerical simulations with a commercial Navier-Stokes solver for a 1.5 stage turbine similar to the model treated in the European Research Project ICAS-GT were conducted. In the framework of a numerical analysis, a validation with experimental results of the test rig at the Technical University of Aachen will be given. In preceding numerical investigations of realistic gas turbine rim cavities with a simplified treatment of the hot gas path (modelling of the main flow path without blades and vanes), so called Kelvin-Helmholtz vortices were found in the area of the gap when using appropriate boundary conditions. The present work shows that these flow instabilities also occur in a 1.5 stage gas turbine model with consideration of the blades and vanes. Therefore, several simulations with different sealing air mass flow rates (CW 7000, 20000, 30000) have been conducted. The results show, that for high sealing air mass flow rates Kelvin-Helmholtz Instabilities are developing. These vortices significantly coin the flow at the rim.

Effect of Purge Flow Swirl on Hot-Gas Ingestion into Turbine Rim Cavities

2016 ◽  
Vol 32 (5) ◽  
pp. 1055-1066 ◽  
Author(s):  
M. B. Zlatinov ◽  
C. S. Tan ◽  
D. Little ◽  
M. Montgomery
Keyword(s):  
Hot Gas ◽  
Flow Swirl ◽  
Purge Flow

Turbine Hub and Shroud Sealing Flow Loss Mechanisms

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Metodi Blagoev Zlatinov ◽  
Choon Sooi Tan ◽  
Matthew Montgomery ◽  
Tito Islam ◽  
Melissa Harris
Keyword(s):  
Flow Characteristics ◽  
Tip Clearance ◽  
Design Parameters ◽  
Tip Clearance Flow ◽  
Suppression Effect ◽  
Clearance Flow ◽  
Flow Loss ◽  
Purge Flow ◽  
Secondary Air ◽  
Axial Turbines

Purge air is injected through seals in the hub and shroud of axial turbines in order to prevent hot gas ingestion into the inter-stage gaps. An investigation into the losses involved with the injection of purge air has been undertaken, with the objectives of answering where the losses are generated, how they are generated, and what are the most effective ways for reducing them. In order to address these questions, a consistent framework for interpreting entropy generation as a measure of loss is developed for turbomachinery applications with secondary air streams. A procedure for factoring out distinct effects is also presented. These tools, applied to steady computations, elucidate four mechanisms by which change in loss generation is brought about due to injection of purge air: a shear layer between purge and main streams, interaction with the passage vortex system that generates radial velocity gradients, changes in wetted loss and tip clearance flow due to an increased degree of reaction, and the potential for reducing tip clearance flow for the case of purge flow injected from the shroud. An emphasis is placed on tracing these effects to specific purge flow characteristics that drive them. The understanding gained provides a rationale for the observed sensitivity of purge flow losses to the design parameters purge air mass fraction and swirl, compared to purge slot axial inclination and gap width. Preswirling of purge flow is less effective in mitigating losses in the case of shroud-injection, since there is a tradeoff with the tip clearance flow suppression effect.

Towards the Automated Optimisation of Liquid Fuel Injector Design for Gas Turbine Engines

2012 ◽  
Author(s):  
Adam L. Comer ◽  
R. Stewart Cant
Keyword(s):  
Mass Flow ◽  
Search Algorithm ◽  
Design Parameters ◽  
Turbine Engines ◽  
Fuel Injector ◽  
Air Mass ◽  
Mass Flow Rates ◽  
Unsteady Rans ◽  
Modelling Assumptions ◽  
Semi Empirical

Given the trend towards leaner combustor primary zones and concurrent increases in injector air mass flow rates for emissions reduction, an automated fuel injector optimisation procedure is proposed for a generic aero-engine combustor. The modelling assumptions and the design of the toolset to be applied for the optimisation study, as well as preliminary results from the computational tools, are presented. The proposed configuration will enable the consideration of the following design parameters: the number of swirlers, the swirl number for each swirler, the air mass flow splits between the swirlers, and the fuel mass flow split for multiple prefilming surfaces. Results from the unsteady RANS spray combustion solver available through the OpenFOAM software package are combined with semi-empirical correlations in order to estimate and capture trends in emissions. Pattern factor and susceptibility to thermoacoustic oscillations are assessed directly through the simulation output. Due to computational costs, only the cruise condition is considered for optimisation, and off-design considerations have been limited to their impact on preliminary combustor sizing and design. A multi-fidelity optimisation strategy incorporating a multi-objective Tabu Search algorithm is also presented in light of the nature of the problem and the complexity of the design spaces constructed from CFD results.

Turbine Hub and Shroud Sealing Flow Loss Mechanisms

2011 ◽  
Author(s):  
Metodi Blagoev Zlatinov ◽  
Choon Sooi Tan ◽  
Matthew Montgomery ◽  
Tito Islam ◽  
Melissa Seco-Soley
Keyword(s):  
Flow Characteristics ◽  
Tip Clearance ◽  
Design Parameters ◽  
Tip Clearance Flow ◽  
Suppression Effect ◽  
Clearance Flow ◽  
Flow Loss ◽  
Purge Flow ◽  
Secondary Air ◽  
Axial Turbines

Purge air is injected through seals in the hub and shroud of axial turbines in order to prevent hot gas ingestion into the inter-stage gaps. An investigation into the losses involved with the injection of purge air has been undertaken, with the objectives of answering where the losses are generated, how they are generated, and what are the most effective ways for reducing them. In order to address these questions, a consistent framework for interpreting entropy generation as a measure of loss is developed for turbomachinery applications with secondary air streams. A procedure for factoring out distinct effects is also presented. These tools, applied to steady computations, elucidate four routes though which change in loss generation is brought about by injection of purge air: a shear layer between purge and main streams, interaction with the passage vortex system that generates radial velocity gradients, changes in wetted loss and tip clearance flow due to an increased degree of reaction, and the potential for reducing tip clearance flow for the case of purge flow injected from the shroud. An emphasis is placed on tracing these effects to specific purge flow characteristics that drive them. The understanding gained provides a rationale for the observed sensitivity of purge flow losses to the design parameters purge air mass fraction and swirl, compared to purge slot axial inclination and gap width. Pre-swirling of purge flow is less effective in mitigating losses in the case of shroud-injection, since there is a tradeoff with the tip clearance flow suppression effect.

Comprehensive Performance Improvement for a 16-Stage Axial Compressor

2021 ◽  
Author(s):  
Grigorii Popov ◽  
Maxim Miheev ◽  
Alexey Vorobyev ◽  
Oleg Baturin ◽  
Vasilii Zubanov
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Pressure Ratio ◽  
Axial Compressor ◽  
Design Parameters ◽  
Air Mass ◽  
Stability Margins ◽  
Gas Dynamic ◽  
Low Efficiency

Abstract The paper describes the process of gas-dynamic modernization of a 16-stage axial compressor of an industrial gas turbine unit. Tests of the baseline variant of the compressor revealed a significant shortfall of efficiency, pressure ratio, and stability margins. In addition, the ongoing work on the modernization of the entire engine sets the task to the authors of not just achieving design parameters but significantly exceeding them (air mass flow rate by 6%, pressure ratio by 2%, adiabatic efficiency by 1% relative to the design values). To achieve these goals, a numerical model of the compressor was developed and validated. The characteristics obtained with its help were carefully analyzed. It was found that the front stage group has low efficiency, and the rear stage group is significantly oversized in terms of mass flow rate. Modernization works were significantly hampered by the presence of many stages and many independent variables. For this reason, the problem was solved in several stages. A separate modernization of the first and rear groups of stages was performed. Moreover, methods of mathematical optimization were used when developing the rear block of 10 stages. Then the working processes of the compressor parts were matched. As a result of the research, a variant was found to modernize the existing 16-stage axial compressor, providing an increase in the air mass flow rate by 18%, adiabatic efficiency by 3.5%, and margins of gas-dynamic stability up to 16%.

Reduced-Order Through-Flow Design Code for Highly Loaded, Cooled Axial Turbines

2013 ◽  
Author(s):  
Majed Sammak ◽  
Marcus Thern ◽  
Magnus Genrup
Keyword(s):  
Mass Flow ◽  
Rotational Speed ◽  
Design Parameters ◽  
Reduced Order ◽  
Through Flow ◽  
Axial Turbines ◽  
Two Stages ◽  
Turbine Design ◽  
Line Design ◽  
Highly Loaded

The development of advanced computational fluid dynamic codes for turbine design does not substitute the importance of mean-line codes. Turbine design involves mean-line design, through-flow design, airfoil design, and finally 3D viscous modeling. The preliminary mean-line design continues to play an important role in early design stages. The aim of this paper was to present the methodology of mean-line designing of axial turbines and to discuss the computational methods and procedures used. The paper presents the Lund University Axial Turbine mean-line code (LUAX-T). LUAX-T is a reduced-order through-flow tool that is capable of designing highly loaded, cooled axial turbines. The stage computation consists of three iteration loops — cooling, entropy, and geometry iteration loop. The stage convergence method depends on whether the stage is part of the compressor turbine (CT) or power turbine (PT) stages, final CT stage, or final PT stage. LUAX-T was developed to design axial single- and twin-shaft turbines, and various working fluid and fuel compositions can be specified. LUAX-T uses the modified Ainley and Mathieson loss model, with the cooling computation based on the m*-model. Turbine geometries were established by applying various geometry correlations and methods. The validation was performed against a test turbine that was part of a European turbine development program. LUAX-T validated the axial PT of the test turbine, which consisted of two stages with rotational speed 13000 rpm. LUAX-T showed good agreement with the available performance data on the test turbine. The paper presented also the mean-line design of an axial cooled twin-shaft turbine. Design parameters were kept within limits of current practice. The total turbine power was 109 MW, of which the CT power was 55 MW. The CT was designed with two stages with a rotational speed of 9500 rpm, while the PT had two stages with a rotational speed of 6200 rpm. The total cooling mass flow was calculated to 31 kg/s, which corresponds to 23 % of compressor inlet mass flow. LUAX-T proved capable of designing uncooled and cooled turbines.

Impact of Combustion Chamber Dynamics on the Temperature Distribution in a Resonator

2019 ◽  
Author(s):  
Michael Betz ◽  
Max Zahn ◽  
Christoph Hirsch ◽  
Thomas Sattelmayer
Keyword(s):  
Temperature Distribution ◽  
Mass Flow ◽  
Acoustic Pressure ◽  
Air Mass ◽  
Hot Gas ◽  
Mean Temperature ◽  
Annular Combustor ◽  
Cooling Phase ◽  
The Mean ◽  
Number Of Cycles

Abstract The results of an experimental study on the influence of the purge air mass flow and the acoustic pressure in an annular combustor test rig on the temperature distribution in resonators with perforated plates at the exit are provided in the paper. The amplitude of the acoustic pressure in the combustor is found to have a high impact on the mean temperature and thus on the performance of the resonators, which originates primarily from the temperature sensitivity of the effective eigenfrequency. In the experiments the temperature in the cavity of one of the resonators is spatially and temporally resolved at 13 locations. The dependence of the mean temperature change on the combustor amplitudes and the purge air mass flow is measured quantitatively. In addition, the axial temperature gradient of the resonator is resolved. The mean temperature changes up to 8% depending on the level of siren forcing. Using acoustic pressure data from the cavity, the velocity of the hot gas jets periodically entering the resonator is calculated. If high amplitudes occur in the combustor and there is no adequate purge air flow in the resonators then hot gas ingestion into the cavity of the resonator occurs, leading to detuning of the resonator and the breakdown of its performance. Once hot gas ingestion occurs, the resonator quickly heats up within a few seconds as the generation of the mixture of hot gas and purge air requires only a low number of cycles. This leads to a thermal runaway of the frequency range of the resonator with high damping. When the combustor returns to quiet operation, a cooling phase with two different time constants is observed.

Influence of Sealing Air Mass Flow on the Velocity Distribution In and Inside the Rim Seal of the Upstream Cavity of a 1.5-Stage Turbine

2003 ◽  
Author(s):  
Dieter E. Bohn ◽  
Achim Decker ◽  
Hongwei Ma ◽  
Michael Wolff
Keyword(s):  
Flow Field ◽  
Velocity Distribution ◽  
Mass Flow ◽  
Flow Rate ◽  
Laser Doppler Velocimetry ◽  
Rotor Blades ◽  
Doppler Velocimetry ◽  
Air Mass ◽  
Guide Vanes ◽  
Hot Gas

The phenomenon of hot gas ingestion at the rim seal section of turbines has been investigated for the front cavity and inside the sealing gap of an 1.5-stage turbine. This paper presents velocity distributions in and inside the rim seal. The experiments were performed using an unsteady 2D Laser Doppler Velocimetry system with a high local and time-based resolution. The hot gas ingestion has been examined for different parameters such as the non-dimensional seal flow rate and includes measurements at 17 circumferential positions with each 5 axial positions at dimensionless radii of 0.985 and 0.952. It is shown that the flow field inside the gap is influenced by the rotor blades as well as by secondary phenomena originating from the guide vanes. The location of hot gas ingestion is moving with the rotor blades and its strength is depending on the amount of seal flow rate. Unsteady interactions between rotor and stator blades have been investigated.

scholarly journals Modelling of Humidity Dynamics for Open-Cathode Proton Exchange Membrane Fuel Cell

2021 ◽  
Vol 12 (3) ◽  
pp. 106
Author(s):  
Fengxiang Chen ◽  
Liming Zhang ◽  
Jieran Jiao
Keyword(s):  
Fuel Cell ◽  
Mass Flow ◽  
Proton Exchange Membrane ◽  
Flow Model ◽  
Transport Theory ◽  
Gas Diffusion ◽  
Proton Exchange ◽  
Operating Conditions ◽  
Output Performance ◽  
Exchange Membrane

The durability and output performance of a fuel cell is highly influenced by the internal humidity, while in most developed models of open-cathode proton exchange membrane fuel cells (OC-PEMFC) the internal water content is viewed as a fixed value. Based on mass and energy conservation law, mass transport theory and electrochemistry principles, the model of humidity dynamics for OC-PEMFC is established in Simulink® environment, including the electrochemical model, mass flow model and thermal model. In the mass flow model, the water retention property and oxygen transfer characteristics of the gas diffusion layer is modelled. The simulation indicates that the internal humidity of OC-PEMFC varies with stack temperature and operating conditions, which has a significant influence on stack efficiency and output performance. In order to maintain a good internal humidity state during operation, this model can be used to determine the optimal stack temperature and for the design of a proper control strategy.

Sign in / Sign up

Export Citation Format

Share Document