Flow Visualization and Topological Analysis of a Turbine Rotor Cascade with Tip Clearance

INTRoDUCTIoNRecentlysignificantattentionhasbeengiventothefinestructurewithintheflowfieldofturbomachinery.Ingeneral,thestudyofthisproblemcontainstwoas-pects.Thefirstistovisualizethesolidsurfaceflowandtopologicallyanalyzethesingularpointstoinves-tigatetheirnumbers,typesandlocationsandtheskinfrictionlinepatternsintheflowfie1dnearesttothewall.Thisaspectaimsatobtainingacertainamountofwallflowinformation.Thesecondaspect,ontheotherhand,carriesoutdetailedflowfieldmeasure-mentsandvisualizationstoac…     

Numerical Analysis of the Aeroelastic Behaviour for the Last Turbine Stage in 3D Transonic Flow

An understanding of the physics of the mutual interaction between gas flow and oscillating blades, and the development of predictive capabilities is essential for improving overall efficiency, durability and reliability. In this study presented the algorithm proposed involving the coupled solution of 3D unsteady flow through a turbine stage and dynamic problem for rotor blades motion by action of aerodynamic forces without separating outer and inner flow fluctuations. There has been performed the calculations for the last stage of the steam turbine under design and off-design regimes. It has investigated the mutual influence of both outer flow non-uniformity and blades oscillations. It has shown that amplitude-frequency spectrum of blade oscillations contains the high frequency harmonics, corresponding to rotor moving one stator blade pitch, and low frequency harmonics caused by blade oscillations and flow non-uniformity downstream from the blade row.     

Photographic Study of Obstacle—Induced Disturbations of Transonic Turbine Cascade Flow

INTRoDUCTIONTheturbineandtalalcompressorcascadeflowsarestronglyeduellcedbyb0ththeupstreamanddown-8treamunsteadybotmdaryconditions.Theunsteadi-ness0fthesllowsisduetotherelativemotionofthestatorandrotorblades.Thispr0blemhasbeeninVeSigatednumericallyandexperimelltallyforovertenyears.ThemajorityofthepapersconsideredtheeffectofuPstreamb0undaryconditions.Sharmaetal.(1992)estAnatedthatthewakesandtheshockwavesatthetrailinedgesofthestatorcascadecausethelossesofther0torcascadefiownearlytwiceaslarg…     

Aerodynamic Optimum Design of Transonic Turbine Cascades Using Genetic Algorithms

INTRoDUCTIoNInmodernturbomachinery,withtheincreasingstageload,thetransoniccascadesbecomemorewidelyused,sothedesignofhighperformancetransoniccas-cadesisacriticaJpracticalproblem.Performanceop-timizationofaerodynamicshapeplaysanimportantroleinthedesigntasksofttirbomachinery,andisanactiveresearchfield.Awidevarietyoftechniqueshavebeendeve1opedtofacethisprobleml1].FuIthermethodsbasedonartificialintelligence-expertsystemtechniqueshavealsobeenintroducedl2].Butthediffusionofauto-matedshapedesigni…     

Experimental Studies on The Mechanism and Control of Secondary Flow Losses in Turbine Cascades

This paper summarizes the results of the authors' 4 year experimental studies on the secondary flow losses in turbine cascades. Cascade wind tunnel experiments were carried out concerning the influence of aspect ratios, incidence, turning angles and outer endwall divergent angles in order to unveil the evolution mechanism of secondary flow losses in turbine cascades without end clearance. Some methods for controlling the secondary flows are investigated including the blade leaning, blade cambering, endwall convergence and leading edge extension at two ends of the blade.     

3D Flow in the Axial—Radial Exhaust Hood of a Steam Turbine

INTRODUCTIONEwhausthoodisaveryimportampartofasteamturbine,especiallytheewhausthoodofthelowpres-sure(LP)partofacondensingsteamturbine.TheffowinLPeallaustisconnectedwithrelativelyhighlossesandsiedcalltupstreaminfluencesonthelastturbinestageanddownstreaminfluencesonthecon-denser.Theflowinastandardtalal-radialLPex-hausthoodaccordingtoFig.1hasbeenstudiedex-perimentallyandtheoreticallyinsomem.delsI1]andexPerimentallyalsoinafullscaleturbineI2].Acompu-tationalmethodwaJsatfirstdevelopedforthei…     

Investigation of Internal Flow in Ultra—Highly Loaded Turbine Cascade by PIV Method

IntroductionSeveral investigations for highly loaded turbineblades have been tried in order to increase the turbineloading and the turbine inlet tempefature["']. Thehighly loaded tUrbine blades are able to reduce both thenumber of blades and the stages. Thus, the highly loadedturbine cascades can reduce the weight and theproduction cost of turbojet-engines. However, in order toachieve the high loading of the turbine blade, the highturning angle is necessmp. As the consequence, the strongt…     

Numerical Simulation of Sub-cooled Cavitating Flow by Using Bubble Size Distribution

A new cavitating model by using bubble size distribution based on mass of bubbles is proposed. Liquid phase is treated with Eulerian framework as a mixture containing minute cavitating bubbles. Vapor phase consists of various sizes of minute vapor bubbles, which is distributed to classes based on their mass. The change of bubble number density for each class was solved by considering the change of bubble mass due to phase change as well as generation of new bubbles due to heterogeneous nucleation. In this method the mass of bubbles is treated as an independent variable, in other word, a new coordinate, and dependant variables are solved in Eulerian framework for spatial coordinates and bubble-mass coordinate. The present method is applied to a cavitating flow in a convergent-divergent nozzle, and the two-phase flow with bubble size distribution and phase change was successfully predicted.     

Analysis of Thermoelastic Crack Problems Using Green–Lindsay Theory

A boundary element method using the Laplace transform in time domain is presented for the analysis of fracture mechanics under thermal shock using the Green and Lindsay (GL) theory of thermoelasticity. The dynamic thermoelastic model of Green and Lindsay is selected to show the effect of thermal wave propagation at finite speed on crack tip stress intensity factor evaluation. The singular behavior of the temperature and displacement fields in the vicinity of the crack tip is modeled by the quarter-point elements. Thermal dynamic stress intensity factor for mode I is evaluated from computed nodal values, using the well-known displacement and traction formulas. The accuracy of the method is investigated through comparison of the results with the available data in literature. Condition where the inertia term plays important role is discussed and variations of dynamic stress intensity factor is investigated. Different relaxation times are chosen to briefly show their effects on stress intensity factor in the Green and Lindsay theory.     

Experimental Investigations of the Three—Dimensional Flow in a Large Deflection Turbine Cascade with Tip Clearance

INTRoDUCTI0NThetipleakaeflowisnowrecognizedasanimpor-tantsourceoflossesinbothcompressorsandturbines,asasourceofcoolingprobleminturbinesandasourceofinstabilityincomPressorsandfans.Manyturbo-maChinimPellersarenotshroudedandtheleakaeflowthroughthetipgaPofthebladeisanunavoidablefaCtorwhichdeterioratestheperformance.Den-tonandCumpsty[1]melltionedabouttwodistinctandequallyimportantaspects.tothetipclearanceflows.First,thereisareducti0ninthebladeforce,there-fore,theworkdone.Thisoccursbecausethe…     

2D CFD Analysis and Experimental Analysis on the Effect of Hub to Tip Ratios on the Performance of 0.6 m Impulse Turbine

The objective of this paper is to present the performance comparison of 2D Computational Fluid Dynamics (CFD) analysis with experimental analysis of 0.6 m impulse turbine with fixed guide vanes for both 0.6 and 0.7 hub to tip ratio (H/T). Also the comparison of 2D CFD analysis of the said turbine with different values of H/T ranging from 0.5 to 0.7. A 2D-cascade model was used for CFD analysis while uni-directional steady flow was used for experimental analysis. The blade and guide vane geometries are based on 0.6 m rotor diameter, with optimum profile, and different H/T of 0.5, 0.6 and 0.7. It was concluded from 2D CFD analysis that 0.5 H/T ratio performances was higher than that of 0.6 and 0.7 H/T at peak efficiency and the operational flow range for 0.5 H/T was found to be wider than that of 0.6 and 0.7 H/T ratio.     

Setup and experimental validation of a 5 kW HT-PEFC stack

This paper presents a performance analysis of a 5 kW_el high temperature polymer electrolyte fuel cell (HT-PEFC) stack. Stack design and sizing is adapted to auxiliary power unit (APU) applications assuming the use of middle distillates. The parameter study comprises the variation of the fuel type (reformate, with pure hydrogen as a reference), the stoichiometry on the anode (1.3–2.7) and cathode (1.25–4.0) sides and the carbon monoxide (CO) concentration (0.9–3.5%) in the reformate. At 0.5 A cm^?2, a coolant inlet temperature of 160 °C, stoichiometric factors of 1.3 on the anode and 2 on the cathode side and reformate operation, two interconnected full stacks produced 5 kW of electric power. The focus of the present work is an examination of the robustness of the full stacks through an analysis of the 70 single cell voltages. By comparison to other published operational parameter studies, this paper makes a significant contribution to the application of the methodology not to single cells or short stacks, but to a stack with technical relevance in the high power class.     

The Problems of Inaccuracy in Flow Capacity Definition by Using Different Numerical Techniques

The results of numerical analysis of turbine flow capacity and other parameters at different turbine rows are presented in this paper. Mass flow calculations by 3D Euler code has been controlled by means of 3D Navier-Stokes code taking into account inlet turbulence intensity and turbulence scale. The use of complicated numerical approaches (3D Euler or 3D Navier-Stokes codes) for mass flow definition demands close attention to quality of numerical techniques. Various reasons of inaccuracy of mass flow definition by using different 3D numerical approaches are analyzed.     

Numerical Modelling of the Aeroelastic Behaviour and Variable Loads for the Turbine Stage in 3D Transonic Flow

Introduction Aeroelastic phenomena in the turbine stage are characterized by instability, continuous interaction and energy exchange between the fluid and the structure; so they cannot be studied properly in the frame of each of uncoupled domains separately (aerodynamics or structural dynamics). The traditional approach in flutter calculations of bladed disks is based on frequency domain analysis[1,2], in which the blade motion is assumed to be a harmonic function of time with a constant phas…     

An Experimental Study on 3—D Flow in an Annular Cascade of High Turning Angle Turbine Blades

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Effect of Placements （horizontal with vertical） on Gas-solid Flow and Particle Impact Erosion in Gate Valve

Gate valve has various placements in the practical usages.Due to the effect of gravity,particle trajectories and erosions are distinct between placements.Thus in this study,gas-solid flow properties and erosion in gate valve for horizontal placement and vertical placement are discussed and compared by using Euler-Lagrange simulation method.The structure of a gate valve and a simplified structure are investigated.The simulation procedure is validated in our published paper by comparing with the experiment data of a pipe and an elbow.The results show that for all investigated open degrees and Stokes numbers(St),there are little difference of gas flow properties and flow coefficients between two placements.It is also found that the trajectories of particles for two placements are mostly identical when St 1,making the erosion independent of placement.With the increase of St,the distinction of trajectories between placements becomes more obvious,leading to an increasing difference of the erosion distributions.Besides,the total erosion ratio of surface T for horizontal placement is two orders of magnitudes larger than that for vertical placement when the particle diameter is 250 μm.     

A Study of 2D Separated Cascade Flow at Large Angles of Attack Using Euler Equations

This paper presents a numerical simulation method developed for separated flow in cascades using the Eulerequations and demonstrates the feasibility of this method.MacCormack's two-steps explicit finite differencescheme is used to discretize the equations in conservation form,and the artificial viscosity is added to the dis-cretized inviscid equations by means of the self-adapted filter technique.The initial separation boundary is givenaccording to simple experimental results.The numerical simulation results including subsonic and transonicturbine cascades flow with or without separation show that the fundamental idea of this numerical method isreasonable and simple.The present study indicates that for solving certain engineering problems it is a simpleand effective tool for adding some viscosity corrections to inviscid flow model,especially the current when theNavier-Stokes equations have not been solved very effectively for various complicated flows in turbomachinery.     

An Analysis of Flow in a Centrifugal Impeller by FEM with k-ε Model

IntnMluctiouIn the passage of a centrifugal impeller, there is notonly a secondary flow toward a suchon-side from aPressure-side along a casing or a hub s~e but also aleakage flow through a clearance between a casings~e and a blade hp. The~, it is imPOI'tant tO clarifysuch a passage flow with regard to the design of acentrifugal turbomashinery with high efficiency.The impeller passage nows have been inveshgatedfrom the flow measurementS with a pressure Probe, ahot-wire anemometer and a LDV…     

On The Analysis of Labyrinth Seal Flow Induced Vibration by Oscillating Fluid Mechanics Method

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Field-Synergy and Figure-of-Merit Analysis of Two Oxide–Water-Based Nanofluids' Flow in Heated Tubes

Field-synergy analysis is performed on the water–oxide nanofluid flow in circular heat sinks to examine the synergetic relation between the flow and temperature fields for heating processes. By varying the Reynolds number and the nanoparticle volume fraction, the convective heat transfer of nanofluid is investigated based on the field synergy number. For heating, the degree of synergy between the velocity and temperature fields of nanofluid flow deteriorates with the Reynolds number increase, leading to a decreased heat transfer performance of the nanofluid. By increasing the particle volume fraction, the degree of synergy between the velocity and temperature fields of the nanofluid flow can be intensified, thus going to convection heat transfer enhancement. After generating results, one can notice that the heat transfer enhancement is strongly dependent on nanoparticle type, Reynolds number, and volume fraction. The results are similar, even if the thermal conductivity of the two considered oxide nanoparticles are quite different. Additionally, a convenient figure of merit that is known as the Mouromtseff number was used as base of comparison, and the results indicated that the considered nanofluids can successfully replace water in specific applications for single-phase forced convection flow in a tube.