Classification of the Hydraulic Behavior Along the No-Load Curve of Francis Turbines

2021 ◽  
Author(s):  
Melissa Fortin ◽  
Bernd Nennemann ◽  
Claire Deschênes ◽  
Sébastien Houde
Keyword(s):  
Pressure Fluctuations ◽  
Operating Conditions ◽  
Flow Structures ◽  
Load Curve ◽  
Flow Topology ◽  
Flow Features ◽  
Hydraulic Turbines ◽  
Operating Points ◽  
Load Conditions

Abstract For hydraulic turbines, no-load is considered a homogeneous family of operating conditions although the literature exposes a wide variety of flow structures depending on many factors. A better understanding of the flow structures developed during NL operation is necessary since they generate pressure fluctuations in the turbine causing significant fatigue damage and reducing the life expectancy of the machines. Hydraulic turbines at model scale show that behavioral trends can be identified for no-load conditions. This paper presents a classification of no-load operating conditions following the swirl level at the runner outlet. The main tendencies linking the cavitation level to the runner speed and the discharge for operating points along no-load curves of different turbines are also detailed. To study the no-load conditions, data from 26 Francis turbines, measured between 2007 and 2020 at the laboratory of Andritz Hydro Canada Inc., are analyzed. This study demonstrates that no-load operating conditions exhibit flow features very similar to those at regular operation with similar runner outlet swirl. The runner acceleration or deceleration with cavitation is related to the flow topology at the runner outlet.

Compressor Design for Multi-Point Operating Conditions of Turbocharged Gasoline Engines

2010 ◽  
Author(s):  
Tao Chen ◽  
Yangjun Zhang ◽  
Xinqian Zheng ◽  
Weilin Zhuge
Keyword(s):  
Internal Combustion Engines ◽  
Gasoline Engine ◽  
Design Method ◽  
Pressure Ratio ◽  
Operating Conditions ◽  
Combustion Engines ◽  
Gasoline Engines ◽  
Compressor Design ◽  
Operating Points ◽  
Load Conditions

Turbocharger compressor design is a major challenge for performance improvement of turbocharged internal combustion engines. This paper presents a multi-point design methodology for turbocharger centrifugal compressors. In this approach, several design operating condition points of turbocharger compressor are considered according to total engine system requirements, instead of one single operating point for traditional design method. Different compressor geometric parameters are selected and investigated at multi-point operating conditions for the flow-solutions of different design objectives. The method has been applied with success to a small centrifugal compressor design of a turbocharged gasoline engine. The results show that the consideration of several operating points is essential to improve the aerodynamic behavior for the whole working range. The isentropic efficiency has been increased by more than 5% at part-load conditions while maintaining the pressure ratio and flow range at full-load conditions of the gasoline engine.

Investigation of the Surge Phenomena in a Centrifugal Compressor Using Large Eddy Simulation

2013 ◽  
Author(s):  
Bernhard Semlitsch ◽  
V. Jyothishkumar ◽  
Mihai Mihaescu ◽  
Laszlo Fuchs ◽  
Ephraim J. Gutmark
Keyword(s):  
Mass Flow ◽  
Centrifugal Compressor ◽  
Numerical Study ◽  
Pressure Fluctuations ◽  
Operating Regime ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Flow Structures ◽  
Compressor Wheel ◽  
Large Eddy

The flow through a ported shroud compressor of an automobile turbocharger is simulated using Large Eddy Simulations. Generally, the compressor is subjected to work within certain range of the mass-flow conditions. Reduction of the operation mass-flow below a certain minimum limit, leads to breakdown of the complete compressor operability. Flow reversal occurs in the compressor wheel, which results in amplification of velocity and pressure fluctuations. Consequentially, large vibratory stresses are induced into the blades under off-design condition and thereby affect the blade life duration detrimentally. The aim of this study is to understand the generation of flow-structures during extreme operable conditions (surge condition) in a centrifugal compressor. The investigation of the appearing flow-structures with the surge phenomenon is essential to explore new methods that improve the stability or the flow-operating regime of the compressor. The complete 360° compressor geometry is utilized in the computational simulations. Further, the transient sliding mesh technique is applied to account for an accurate prediction of the mesh motion and thus, the geometrical interaction between the impeller and the stationary diffuser. The numerical results are compared with available experimental measurements obtained under the same operating conditions (design and near-surge condition). The rotating stall instability is predicted using FFT data analysis. Furthermore, the numerical study captures the low frequency peak characterizing the global instability of the surge condition.

Experimental Investigation of Draft Tube Inlet Velocity Field of a Propeller Turbine

2012 ◽  
Vol 134 (10) ◽  
Author(s):  
Jean-Mathieu Gagnon ◽  
Vincent Aeschlimann ◽  
Sébastien Houde ◽  
Felix Flemming ◽  
Stuart Coulson ◽  
...  
Keyword(s):  
Swirling Flow ◽  
Draft Tube ◽  
Secondary Flows ◽  
Operating Conditions ◽  
Flow Structures ◽  
Test Cases ◽  
Yield Information ◽  
Hydraulic Turbines ◽  
Dominant Frequencies ◽  
Flow Nonuniformity

The draft tube of reaction hydraulic turbines is subject to numerous investigations since it accounts for a significant portion of the energy recovery. But even with up-to-date computational fluid dynamics methodologies, simulating the draft tube flow remains highly challenging since it is a diverging swirling flow that may undergo flow separations and become dominated by unsteady secondary flows. Within the framework of a collaborative research project on the flow dynamics of a propeller turbine model, the flow at the inlet region of the draft tube was studied using 2D-laser Doppler velocimetry (2D-LDV). Measurements were used to detect and characterize the flow structures at three operating conditions: partial discharge, near best efficiency, and full-load conditions. The paper presents analysis based on phased-averaged velocity fields to yield information on fluctuations and dominant frequencies according to runner positions. The main features detected are the flow nonuniformity at the runner exit and the secondary flow structures associated with the runner hub wake. Those results are part of a larger database aimed at providing test cases for the validation of numerical simulation strategies.

Visualization of Three-Dimensional Flow Structures Caused by Rotating Instability

2019 ◽  
Author(s):  
Julija Peter ◽  
Paul Uwe Thamsen
Keyword(s):  
High Speed ◽  
Spectral Characteristics ◽  
Pressure Fluctuations ◽  
Three Dimensional ◽  
Flow Structures ◽  
Experimental Investigations ◽  
Flow Topology ◽  
Time Resolved ◽  
Characteristic Flow ◽  
Rotating Instability

Abstract The present study deals with the flow phenomenon Rotating Instability (RI), which is predominantly observed in axial compressors at off-design conditions e.g. near stall. It potentially induces noise and triggers blade vibrations. Despite numerous studies, the characteristics and the source of RI are not completely understood. The objective of this work is to identify and to visualize characteristic flow topology corresponding to RI by means of Stereo High Speed Particle Image Velocimetry (PIV). The experimental investigations were carried out in an annular compressor stator cascade with and without hub clearance at an inflow Mach number of Ma = 0.4 and the Reynolds number of Re = 300 000. The time-resolved 3C flow field is measured in a single blade passage in planes tangential to the hub. Additionally, the time-resolved pressure fluctuations are captured synchronously to the PIV system. By using combined correlation techniques the spectral characteristics, the spatial extension of the RI and the characteristic flow structures were identified and visualized in configurations with and without hub clearance. The investigations point out that the general flow mechanism of RI is similar in compressor cascades with and without hub clearance. Overall, this work gives important insights into the complex phenomenon Rotating Instability, which can be taken into account when developing compressors in the future.

Flow Features Analysis of Throttle Notches of Proportional Direct Valve

2011 ◽  
Vol 189-193 ◽  
pp. 2285-2288
Author(s):  
Wen Hua Jia ◽  
Chen Bo Yin ◽  
Guo Jin Jiang
Keyword(s):  
Fluid Flow ◽  
Dynamic Behavior ◽  
Flow Rate ◽  
Discharge Coefficient ◽  
3D Models ◽  
Operating Conditions ◽  
Flow Models ◽  
Flow Features ◽  
Rate Discharge ◽  
Spool Valve

Flow features, specially, flow rate, discharge coefficient and efflux angle under different operating conditions are numerically simulated, and the effects of shapes and the number of notches on them are analyzed. To simulate flow features, 3D models are developed as commercially available fluid flow models. Most construction machineries in different conditions require different actions. Thus, in order to be capable of different actions and exhibit good dynamic behavior, flow features should be achieved in designing an optimized proportional directional spool valve.

Experimental investigation of isothermal and reacting flow characteristics downstream of axisymmetric bluff body stabilizers under stratified or fully premixed inlet mixture conditions

2020 ◽  
Author(s):  
Γεώργιος Πατεράκης
Keyword(s):  
Experimental Investigation ◽  
Turbulent Flow ◽  
Bluff Body ◽  
Operating Conditions ◽  
Reacting Flow ◽  
Wide Range ◽  
Flow Features ◽  
Air Mixing ◽  
The Impact ◽  
Stratified Flames

The current work describes an experimental investigation of isothermal and turbulent reacting flow field characteristics downstream of axisymmetric bluff body stabilizers under a variety of inlet mixture conditions. Fully premixed and stratified flames established downstream of this double cavity premixer/burner configuration were measured and assessed under lean and ultra-lean operating conditions. The aim of this thesis was to further comprehend the impact of stratifying the inlet fuelair mixture on the reacting wake characteristics for a range of practical stabilizers under a variety of inlet fuel-air settings. In the first part of this thesis, the isothermal mean and turbulent flow features downstream of a variety of axisymmetric baffles was initially examined. The effect of different shapes, (cone or disk), blockage ratios, (0.23 and 0.48), and rim thicknesses of these baffles was assessed. The variations of the recirculation zones, back flow velocity magnitude, annular jet ejection angles, wake development, entrainment efficiency, as well as several turbulent flow features were obtained, evaluated and appraised. Next, a comparative examination of the counterpart turbulent cold fuel-air mixing performance and characteristics of stratified against fully-premixed operation was performed for a wide range of baffle geometries and inlet mixture conditions. Scalar mixing and entrainment properties were investigated at the exit plane, at the bluff body annular shear layer, at the reattachment region and along the developing wake were investigated. These isothermal studies provided the necessary background information for clarifying the combustion properties and interpreting the trends in the counterpart turbulent reacting fields. Subsequently, for selected bluff bodies, flame structures and behavior for operation with a variety of reacting conditions were demonstrated. The effect of inlet fuel-air mixture settings, fuel type and bluff body geometry on wake development, flame shape, anchoring and structure, temperatures and combustion efficiencies, over lean and close to blow-off conditions, was presented and analyzed. For the obtained measurements infrared radiation, particle image velocimetry, laser doppler velocimetry, chemiluminescence imaging set-ups, together with Fouriertransform infrared spectroscopy, thermocouples and global emission analyzer instrumentation was employed. This helped to delineate a number of factors that affectcold flow fuel-air mixing, flame anchoring topologies, wake structure development and overall burner performance. The presented data will also significantly assist the validation of computational methodologies for combusting flows and the development of turbulence-chemistry interaction models.

Scale Resolving CFD Investigations of Aerothermal Field and Emissions of a Lean Burn Aeroengine Combustor

2021 ◽  
Author(s):  
S. Paccati ◽  
L. Mazzei ◽  
A. Andreini ◽  
S. Patil ◽  
S. Shrivastava ◽  
...  
Keyword(s):  
Pressure Fluctuations ◽  
Computational Cost ◽  
Flame Stabilization ◽  
Operating Conditions ◽  
Tetrahedral Mesh ◽  
Main Stream ◽  
Nox Emissions ◽  
Lean Burn ◽  
Emission Data ◽  
Hexahedral Elements

Abstract Due to the increasingly stringent international limitations in terms of NOx emissions, the development of new combustor concepts has become extremely important in order for aircraft engines to comply with these regulations. In this framework, lean-burn technology represents a promising solution and several studies and emission data from production engines have proven that it is more promising in reducing NOx emissions than rich-burn technology. Considering the drawbacks of this combustion strategy (flame stabilization, flashback or blowout or the occurrence of large pressure fluctuations causing thermo-acoustics phenomena) as well as the difficulties and the high costs related to experimental campaigns at relevant operating conditions, Computational Fluid Dynamics (CFD) plays a key role in deepening understanding of the complex phenomena that are involved in such reactive conditions. During last years, large research efforts have been devoted to develop new advanced numerical strategies for high-fidelity predictions in simulating reactive flows that feature strong unsteadiness and high levels of turbulence intensity with affordable computational resources. In this sense, hybrid RANS-LES models represent a good compromise between accurate prediction of flame behaviour and computational cost with respect to fully-LES approaches. Stress-Blended Eddy Simulation (SBES) is a new global hybrid RANS-LES methodology which ensures an improved shielding of RANS boundary layers and a more rapid RANS-LES “transition” compared to other hybrid RANS-LES formulations. In the present work, a full annular aeronautical lean-burn combustor operated at real conditions is investigated from a numerical point of view employing the new SBES approach using poly-hexcore mesh topology, which allows to adopt an isotropic grid for more accurate scale-resolving calculations by means of fully regular hexahedral elements in the main stream. The results are compared to experimental data and to previous reference numerical results obtained with Scale Adaptive Simulation formulation on a tetrahedral mesh grid in order to underline the improvements achieved with the new advanced numerical setup.

Unsteady Conjugate Heat Transfer Investigation of a Multistage Steam Turbine in Warm-Keeping Operation With Hot Air

2018 ◽  
Author(s):  
Piotr Łuczyński ◽  
Dennis Toebben ◽  
Manfred Wirsum ◽  
Wolfgang F. D. Mohr ◽  
Klaus Helbig
Keyword(s):  
Heat Transfer ◽  
Conjugate Heat Transfer ◽  
Flow Patterns ◽  
Operating Conditions ◽  
Angle Of Incidence ◽  
Time Step ◽  
Hot Air ◽  
Wide Range ◽  
Vortex Systems ◽  
Operating Points

In recent decades, the rising share of commonly subsidized renewable energy especially affects the operational strategy of conventional power plants. In pursuit of flexibility improvements, extension of life cycle, in addition to a reduction in start-up time, General Electric has developed a product to warm-keep high/intermediate pressure steam turbines using hot air. In order to optimize the warm-keeping operation and to gain knowledge about the dominant heat transfer phenomena and flow structures, detailed numerical investigations are required. Considering specific warm-keeping operating conditions characterized by high turbulent flows, it is required to conduct calculations based on time-consuming unsteady conjugate heat transfer (CHT) simulations. In order to investigate the warm-keeping process as found in the presented research, single and multistage numerical turbine models were developed. Furthermore, an innovative calculation approach called the Equalized Timescales Method (ET) was applied for the modeling of unsteady conjugate heat transfer (CHT). The unsteady approach improves the accuracy of the stationary simulations and enables the determination of the multistage turbine models. In the course of the research, two particular input variables of the ET approach — speed up factor (SF) and time step (TS) — have been additionally investigated with regard to their high impact on the calculation time and the quality of the results. Using the ET method, the mass flow rate and the rotational speed were varied to generate a database of warm-keeping operating points. The main goal of this work is to provide a comprehensive knowledge of the flow field and heat transfer in a wide range of turbine warm-keeping operations and to characterize the flow patterns observed at these operating points. For varying values of flow coefficient and angle of incidence, the secondary flow phenomena change from well-known vortex systems occurring in design operation (such as passage, horseshoe and corner vortices) to effects typical for windage, like patterns of alternating vortices and strong backflows. Furthermore, the identified flow patterns have been compared to vortex systems described in cited literature and summarized in the so-called blade vortex diagram. The comparison of heat transfer in the form of charts showing the variation of the Nusselt-numbers with respect to changes in angle of incidence and flow coefficients at specific operating points is additionally provided.

Double Scroll Turbine for Automotive Applications: Engine Operating Point Versus Dynamic Blade Stress From Forced Response Vibration

2018 ◽  
Author(s):  
David Hemberger ◽  
Roberto De Santis ◽  
Dietmar Filsinger
Keyword(s):  
Pulse Energy ◽  
Internal Combustion Engines ◽  
Forced Response ◽  
Operating Conditions ◽  
Blade Vibration ◽  
Structural Dynamic ◽  
Vibration Excitation ◽  
Engine Combustion ◽  
Operating Points ◽  
Combustion Cycle

As a means of meeting ever increasing emissions and fuel economy demands car manufacturers are using aggressive engine downsizing. To maintain the power output of the engine turbocharging is typically used. Compared to Mono scroll turbines, with a multi-entry system the individual volute sizing can be better matched to the single mass flow pulse from the engine cylinders. The exhaust pulse energy can be better utilised by the turbocharger turbine improving turbocharger response. Additionally the interaction of the engine exhaust pulses can be better avoided, improving the scavenging of the engine. Besides the thermodynamic advantages, the multi-entry turbine represents a challenge to the structural dynamic design of the turbine. A higher number of turbine wheel resonance points can be expected during operation. In addition, the increased use of exhaust pulse energy leads to a distinct accentuation of the blade vibration excitation. Using validated engine models, the interaction of the multi-entry turbine with the engine has been analyzed and various operating points, which may be critical for the blade vibration excitation, have been classified. These operating points deliver the input variables for unsteady computational flow dynamics (CFD) analyses. From these calculations unsteady blade forces were derived providing the necessary boundary conditions for the structural dynamic analyses by spatially and temporally high-resolved absolute pressures on the turbine surface. Goal of the investigation is to identify critical operating conditions. Important is also to investigate the effect of a scroll connection valve on blade excitation. The investigations utilize validated tools that were introduced and successfully applied to several turbine types in a series of publications over recent years. It can be stated that the engine operating condition and the admission type significantly influence the forced response reaction of the blade to the different excitation orders (EO). In case of equal admission even (or multiples of two) EOs generate the largest dynamic blade stress as can be expected due to the two turbine inlet segments. This reaction also increases with the engine speed. In the case of unequal admission, the odd EOs produce the largest forced response reaction. The maximum dynamic blade stress occurs in the region where the scroll connection is just closed. Above all, the scroll connection valve influences the Beta value and thus the basic behavior — unequal or equal admission. It has been possible to reconstruct the forced response behavior of the turbine blade within an engine combustion cycle. For the first time it could be shown for a double scroll application that there is a significant dynamic blade stress change dependent on the engine crankshaft angle. Certainly, due to the inertia of the mass and damping (mass, structure, flow), the blade will not exactly follow the predicted course. However, it is clear that the transient processes within an engine combustion cycle will affect the dynamic blade stress. This applies to the turbine wheels investigated in the work at hand with low damping, high eigenfrequencies and the considered internal combustion engines — as they are typically used in the passenger car sector.

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