Aerodynamic Investigation of the Performance of a Two Stage Axial Turbine at Design and Off-Design Conditions

2011 ◽  
Author(s):  
Sherif A. Abdelfattah ◽  
Hicham A. Chibli ◽  
M. T. Schobeiri
Keyword(s):  
High Pressure ◽  
Flow Field ◽  
Flow Characteristics ◽  
Operating Conditions ◽  
Numerical Dissipation ◽  
Two Stage ◽  
Engine Operation ◽  
Axial Turbine ◽  
Secondary Loss ◽  
Loss Mechanisms

This paper describes numerical aerodynamic investigations of a two-stage, high pressure axial turbine at design and off-design operating conditions. The flow field in a high pressure turbine is highly complex due to unsteadiness of the flow and the various effects of blade row interaction. Blade loss mechanisms generally include primary and secondary loss mechanisms. Examples of primary loss mechanisms include boundary layer losses, shock losses and mixing losses, whereas examples of secondary losses include tip leakage losses and end wall losses which both create secondary flow characteristics. Although modern numerical analysis techniques have provided good understanding of the flow field, it is still difficult to accurately predict impact due to the aforementioned loss effects. This is generally due to errors predicting in boundary layers, transition as well as false entropy generation due to numerical dissipation. When a turbine is operated at off-design conditions the primary and secondary loss effects are further increased and create further reductions in engine efficiency. In this study a numerical model of the two-stage axial turbine was constructed and run under boundary conditions designed to mimic the operating conditions applied during engine operation. The shear stress transport (SST) turbulence model was selected for its versatility in turbomachinery applications. A comparison was made between both experimentally measured efficiencies and numerically predicted efficiencies.

scholarly journals A New Method to Determine the Impact of Individual Field Quantities on Cycle-to-Cycle Variations in a Spark-Ignited Gas Engine

Energies ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 4136
Author(s):  
Clemens Gößnitzer ◽  
Shawn Givler
Keyword(s):  
Kinetic Energy ◽  
Flow Field ◽  
Turbulent Kinetic Energy ◽  
Negative Impact ◽  
Operating Conditions ◽  
Engine Operation ◽  
Gas Engine ◽  
Cycle Simulation ◽  
Simulation Results ◽  
The Impact

Cycle-to-cycle variations (CCV) in spark-ignited (SI) engines impose performance limitations and in the extreme limit can lead to very strong, potentially damaging cycles. Thus, CCV force sub-optimal engine operating conditions. A deeper understanding of CCV is key to enabling control strategies, improving engine design and reducing the negative impact of CCV on engine operation. This paper presents a new simulation strategy which allows investigation of the impact of individual physical quantities (e.g., flow field or turbulence quantities) on CCV separately. As a first step, multi-cycle unsteady Reynolds-averaged Navier–Stokes (uRANS) computational fluid dynamics (CFD) simulations of a spark-ignited natural gas engine are performed. For each cycle, simulation results just prior to each spark timing are taken. Next, simulation results from different cycles are combined: one quantity, e.g., the flow field, is extracted from a snapshot of one given cycle, and all other quantities are taken from a snapshot from a different cycle. Such a combination yields a new snapshot. With the combined snapshot, the simulation is continued until the end of combustion. The results obtained with combined snapshots show that the velocity field seems to have the highest impact on CCV. Turbulence intensity, quantified by the turbulent kinetic energy and turbulent kinetic energy dissipation rate, has a similar value for all snapshots. Thus, their impact on CCV is small compared to the flow field. This novel methodology is very flexible and allows investigation of the sources of CCV which have been difficult to investigate in the past.

Experimental and Numerical Study on Pressure Losses and Flow Fluctuations in a High-Pressure Valve Assembly of Steam Turbine Governing System

2020 ◽  
Author(s):  
Vaclav Slama ◽  
Lukas Mrozek ◽  
Bartolomej Rudas ◽  
David Simurda ◽  
Jindrich Hala ◽  
...  
Keyword(s):  
High Pressure ◽  
Flow Field ◽  
Numerical Simulations ◽  
Pressure Loss ◽  
Operational Reliability ◽  
Operating Conditions ◽  
The Real ◽  
Pressure Losses ◽  
Flow Fluctuations ◽  
Valve Assembly

Abstract Aerodynamic measurements and numerical simulations carried out on a model of a high-pressure valve assembly used for nozzle governing of a turbine with 135MW output are described in this paper. Aim of the study is to investigate effects of control valve’s strainers on pressure losses and unsteadiness in the flow field. It is an important task since undesirable flow fluctuations can lead to operational reliability issues. Measurements were carried out in the Aerodynamic laboratory of the Institute of Thermomechanics of the Czech Academy of Sciences (IT) where an aerodynamic tunnel is installed. Numerical simulations were carried out in the Doosan Skoda Power (DSP) Company using ANSYS software tools. The experimental model consists of one of two identical parts of the real valve assembly. It means it consists of an inlet pipeline, a stop valve, a valve chamber with two independent control valves, its diffusers and outlet pipelines. The numerical model consists of both assembly parts and includes also an A-wheel control stage in order to simulate the real turbine operating points. The different lifts of the main cone in each control valve for its useful combinations were investigated. Results were evaluated on the model with control valve’s strainers, which were historically used in order to stabilize the flow, and without them. The results of the experimental measurement were compared with the numerical results in the form of pressure losses prediction. From measured pressure fluctuations, it was found out where and for which conditions a danger of flow instabilities occurs. It can be concluded that there is a border, in terms of operating conditions, where the flow field starts to be unstable and this border is different dependent of the fact whether the control valve’s strainers are used or not. Therefore, the areas of safe and danger operational reliability can be predicted. The influence of the control valve’s strainers on the maximal amplitude of periodic fluctuations appears only for the cases when valves are highly overloaded. For normal operating conditions, there is no difference. As a result, the control valve’s strainers do not have to be used in standard applications of valve assemblies. Furthermore, a loss model for valve pressure loss estimation could be updated. Therefore, a pressure loss should be predicted with a sufficient accuracy for each new turbine bid with similar valve assemblies.

scholarly journals Investigation of the Optimum Clocking Position in a Two-Stage Axial Turbine

2005 ◽  
Vol 2005 (3) ◽  
pp. 202-210 ◽  
Author(s):  
Dieter Bohn ◽  
Sabine Ausmeier ◽  
Jing Ren
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Preliminary Design ◽  
Two Stage ◽  
Axial Turbine ◽  
Sliding Mesh ◽  
Field Distributions ◽  
Unsteady Simulation

A frozen rotor approach in a steady calculation and a sliding mesh approach in an unsteady simulation are performed in a stator clocking investigation. The clocking is executed on the second stator in a two-stage axial turbine over several circumferential positions. Flow field distributions as well as the estimated performances from two approaches are compared with each other. The optimum clocking positions are predicted based on the estimated efficiency from the two approaches. The consistence of the optimum clocking positions is discussed in the paper. The availability and the limit of the frozen rotor approach in predicting the optimum clocking position is analyzed. It is concluded that the frozen rotor approach is available to search the optimum clocking position in the preliminary design period, although it misses some features of the unsteady flow field in the multistage turbines.

scholarly journals Flow Distortion Into the Core Engine for an Installed Variable Pitch Fan in Reverse Thrust Mode

2020 ◽  
Author(s):  
David John Rajendran ◽  
Vassilios Pachidis
Keyword(s):  
Flow Field ◽  
Total Pressure ◽  
Reverse Flow ◽  
Ground Plane ◽  
Operating Conditions ◽  
Flow Distortion ◽  
Engine Operation ◽  
Variable Pitch ◽  
The Core ◽  
Reverse Thrust

Abstract The flow distortion at core engine entry for a Variable Pitch Fan (VPF) in reverse thrust mode is described from a realistic flow field obtained using an integrated airframe-engine model. The model includes the VPF, core entry splitter, complete bypass nozzle flow path wrapped in a nacelle and installed to an airframe in landing configuration through a pylon. A moving ground plane to mimic the rolling runway is included. 3D RANS solutions are generated at two combinations of VPF stagger angle and rotational speed settings for the entire aircraft landing run from 140 to 20 knots. The internal reverse thrust flow field is characterized by bypass nozzle lip separation, pylon wake and recirculation of flow turned back from the VPF. A portion of the reverse stream flow turns 180° with separation at the splitter leading edge to feed the core engine. The core engine feed flow exhibits circumferential and radial non-uniformities that depend on the reverse flow development at different landing speeds. The temporal dependence of the distorted flow features is also explored by an URANS analysis. Total pressure and swirl angle distortion descriptors, as defined by the Society of Automotive Engineers (SAE) S-16 committee, and, total pressure loss into the core engine are described for the core feed flow at different operating conditions and landing speeds. It is observed that the radial intensity of total pressure distortion is critical to core engine operation, while the circumferential intensity is within acceptable limits. Therefore, the baseline sharp splitter edge is replaced by two larger rounded splitter edges of radii, ∼0.1x and ∼0.2x times the core duct height. This was found to reduce the radial intensity of total pressure distortion to acceptable levels. The description of the installed core feed flow distortion, as described in this study, is necessary to ascertain stable core engine operation, which powers the VPF in reverse thrust mode.

The 2-Stage Axial Turbine Test Facility “LISA”

2001 ◽  
Author(s):  
M. Sell ◽  
J. Schlienger ◽  
A. Pfau ◽  
M. Treiber ◽  
R. S. Abhari
Keyword(s):  
Unsteady Flow ◽  
Mass Flow ◽  
Measurement Techniques ◽  
Operating Conditions ◽  
Test Facility ◽  
Two Stage ◽  
Axial Turbine ◽  
Aerodynamic Pressure ◽  
Second Stage ◽  
The Impact

This paper describes the design and construction of a new two stage axial turbine test facility, christened “Lisa”. The research objective of the rig is to study the impact (relevance) of unsteady flow phenomena upon the aerodynamic performance, this being achieved through the use of systematic studies of parametric changes in the stage geometry and operating point. Noteworthy in the design of the rig is the use of a twin shaft arrangement to decouple the stages. The inner shaft carries the load from the first stage whilst the outer is used with an integral torque-meter to measure the loading upon the second stage alone. This gives an accurate measurement of the loading upon the aerodynamically representative second stage, which possesses the correct stage inlet conditions in comparison to the full two stage machine which has an unrealistic axial inlet flow at the first stator. A calibrated Venturi nozzle measures the mass flow at an accuracy of below 1%, from which stage efficiencies can be derived. The rig is arranged in a closed loop system. The turbine has a vertical arrangement and is connected through a gear box to a generator system that works as a brake to maintain the desired operating speed. The turbine exit is open to ambient pressure. The rig runs at a low pressure ratio of 1.5. The maximum Mach number at stator exit is 0.3 at an inlet pressure of 1.5 bar. The maximum mass flow is 14 kg/sec. Nominal rotor design speed is 3000 RPM. The tip to hub blade ratio is 1.29, and the nominal axial chord is 50 mm. The rig is designed to accommodate a broad range of measurement techniques, but with a strong emphasis upon unsteady flow methods, for example fast response aerodynamic pressure probes for time-resolved flow measurements. The first section of this paper describes the overall test facility hardware. This is followed by a detailed focus on the torque measurement device including stage efficiency measurements at operating conditions in Lisa. Discussion of measurement techniques completes the paper.

Design of a High-Speed Rotating Test Rig for Adaptive Seal Systems

2015 ◽  
Author(s):  
Laura S. Beermann ◽  
Corina Höfler ◽  
Hans-Jörg Bauer
Keyword(s):  
High Pressure ◽  
Flow Field ◽  
High Speed ◽  
Operating Conditions ◽  
Turbine Engines ◽  
Parameter Study ◽  
Test Rig ◽  
Swirl Chamber ◽  
Mass Flows ◽  
Gap Width

Gas turbine engines are subject to increased performance and improved efficiency, which leads to rising core temperatures with additional cooling needs. Reducing the parasitic leakage in the secondary flow system is important to meet the challenging requirements. New seal designs have to be tested and optimized at engine like conditions, like high pressure of up to 9 bar and surface speed of up to 280 m/s as well as an adjusted flow field. Flexible seal designs are an innovative approach to reduce leakage mass flows significantly. Axial and radial movements during transient operating conditions can be compensated easily, thus allowing a smaller gap width and minimizing rub and heat load. This paper describes the design and construction of a new rotating test rig facility. To the knowledge of the authors, this is the only test rig with an adjustable gap width and flow field in a high pressure and speed range. The facility is capable of up to 8 bar differential pressure across the seal and up to 4 bar back pressure. The high revolution engine facilitates a surface speed of up to 280 m/s. A traversable casing allows a quick change of the gap width during operation and simulates radial and axial rotor/stator movements in the engine. The seal movement as well as the resulting gap width are measured during operation to fully understand the seal behavior. An important feature of the new test rig is the continuously adjustable pre-swirl system. It has been designed to cover the different flow conditions in the real engine. Therefore, a RANS parameter study of the pre-swirl chamber has been conducted, which shows the adjustability of different pre-swirl ratios for constant and changing inlet mass flows.

Investigation of 3D Unsteady Flows in a Two Stage Shrouded Axial Turbine Using Stereoscopic PIV and FRAP: Part I — Interstage Flow Interactions

2006 ◽  
Author(s):  
L. Porreca ◽  
Y. I. Yun ◽  
A. I. Kalfas ◽  
S. J. Song ◽  
R. S. Abhari
Keyword(s):  
Flow Field ◽  
Measurement Techniques ◽  
Flow Analysis ◽  
Three Dimensional ◽  
Fast Response ◽  
Design Flow ◽  
Main Stream ◽  
Two Stage ◽  
Axial Turbine ◽  
Improved Design

A detailed flow analysis has been carried out in a two-stage shrouded axial turbine by means of intrusive and non-intrusive measurement techniques. Multi-sensor Fast Response Aerodynamic Probe (FRAP) and 3D-PIV system were applied at two locations downstream of the first and second rotors. Several radial planes were measured focusing on the blade tip region in order to obtain a unique set of steady and unsteady velocity data. The investigation deals with the aerodynamics and kinematics of flow structures downstream of the first and second rotors and their interaction with the main flow in a partially shrouded turbine typical of industrial application. The first part of this work is focused on the flow field downstream of the first rotor while the second part studies the leakage flow in the cavity of the second rotor and its interaction with the main stream. The interstage region is characterized by interactions between the tip passage vortex and a vortex caused by the recessed shroud platform design. Flow coming from the blade passage suddenly expands and migrates radially in the cavity region causing a localized total pressure drop. The time evolution of these vortical structures and the associated downstream unsteady loss generation are analyzed. The partial shroud design adopted in this geometry is beneficial in terms of blade stress and thermal load; however flow field downstream of the first rotor is highly three dimensional due to the intense interaction between cavity and main streams. A flow interpretation is provided and suggestions for improved design are finally addressed based on the steady and unsteady flow analysis.

Blade stacking and clocking effects in two-stage high-pressure axial turbine

2019 ◽  
Vol 91 (8) ◽  
pp. 1133-1146
Author(s):  
Kaddour Touil ◽  
Adel Ghenaiet
Keyword(s):  
High Pressure ◽  
Leading Edge ◽  
Maximum Efficiency ◽  
Two Stage ◽  
Axial Turbine ◽  
Content Type ◽  
Second Stage ◽  
Blade Row ◽  
Practical Implications ◽  
Isentropic Efficiency

Purpose The purpose of this paper is to characterize the blade–row interaction and investigate the effects of axial spacing and clocking in a two-stage high-pressure axial turbine. Design/methodology/approach Flow simulations were performed by means of Ansys-CFX code. First, the effects of blade–row stacking on the expansion performance were investigated by considering the stage interface. Second the axial spacing and the clocking positions between successive blade–rows were varied, the flow field considering the frozen interface was solved, and the flow interaction was assessed. Findings The axial spacing seems affecting the turbine isentropic efficiency in both design and off-design operating conditions. Besides, there are differences in aerodynamic loading and isentropic efficiency between the maximum efficiency clocking positions where the wakes of the first-stage vanes impinge around the leading edge of the second-stage vanes, compared to the clocking position of minimum efficiency where the ingested wakes pass halfway of the second-stage vanes. Research limitations/implications Research implications include understanding the effects of stacking, axial spacing and clocking in axial turbine stages, improving the expansion properties by determining the adequate spacing and locating the leading edge of vanes and blades in both first and second stages with respect to the maximum efficiency clocking positions. Practical implications Practical implications include improving the aerodynamic design of high-pressure axial turbine stages. Originality/value The expansion process in a two-stage high-pressure axial turbine and the effects of blade–row spacing and clocking are elucidated thoroughly.

scholarly journals Flow characterization in an axial micro-hydroturbine model

2021 ◽  
Vol 2127 (1) ◽  
pp. 012002
Author(s):  
D A Suslov ◽  
S I Shtork ◽  
I V Litvinov ◽  
E U Gorelikov
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
High Efficiency ◽  
Swirling Flow ◽  
Flow Characteristics ◽  
Laser Doppler Anemometer ◽  
Operating Conditions ◽  
Swirl Number ◽  
Operation Conditions ◽  
Flow Characterization

Abstract The flow characteristics behind the runner of an air model of a propeller-type micro-hydroturbine were studied in detail by varying the operation conditions from part-load to high overload. The Reynolds number was varied from 3×104 to 9×104, and the swirl number from 0.7 to -0.4. An automated laser-Doppler anemometer (LDA) system for non-contact optical diagnostics was used to perform detailed measurements of the flow field distribution, including the profiles of two components of averaged velocities and pulsations and LDA signal spectra. Based on the results, a correlation was found between the identified features of the development of the flow structure under changing operating conditions of the hydroturbine and the nature of the evolution of the integral swirl number, which determines the state of the swirling flow. This can be used to develop recommendations for expanding the range of regulation of hydroturbine operation while maintaining high efficiency.

Experimental and Numerical Investigation of Near-Tip Flow Field in an Axial Flow Compressor Rotor: Part I — Flow Characteristics at Stable Operating Conditions

2013 ◽  
Author(s):  
Yanhui Wu ◽  
Junfeng Wu ◽  
Haoguang Zhang ◽  
Wuli Chu
Keyword(s):  
Flow Field ◽  
Fourier Transformation ◽  
Flow Characteristics ◽  
Operating Conditions ◽  
Small Scale ◽  
Flow Mechanism ◽  
Compressor Rotor ◽  
Stable Operating ◽  
Stable Conditions ◽  
Casing Pressure

Systematical casing pressure measurements were undertaken to supplement instantaneous experiment data to available database of a high-speed small-scale compressor rotor, which was crucial for understanding the flow mechanism of short-length scale stall inception. At the same time, improved full-annulus simulations were conducted to assist in interpretation of experimental observations. In Part I of current investigation, FFT (fast Fourier transformation) and STFT (short time Fourier transformation) analyses of instantaneous casing pressure signals were conducted to conclude flow characteristics near casing at stable operating conditions, and reasonable explanation of experimental observations was given in combination with the current and previous numerical results. FFT analyses of casing pressure signals showed a characteristic hump with varying band lower than blade passing frequency (BPF) appeared at near-stall stable conditions. This indicated that an unsteady phenomenon emerged from the near-tip flow field for the test rotor. The variation in the amplitude of characteristic hump implied that underlying flow mechanism leading to the emergence of unsteady phenomenon originated from a location near leading edge and within passage. Further STFT analyses showed that the active frequency of this unsteady phenomenon varied with time, thus leading to the appearance of excitation band in FFT analysis results. FFT and STFT analyses of monitoring results of numerical probes arranged in absolute frame showed a similar unsteady phenomenon appeared in the simulated near-tip flow field. Detailed analyses of simulated instantaneous flow fields and comparison with measured flow characteristics indicated that the unsteady flow phenomenon observed in experiments was equivalent to rotating instability (RI) as far as non-uniform tip loading distribution was concerned, and the formation and activity of tip secondary vortex (TSV) was the flow mechanism of emergence of RI.

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