Numerical Investigation on Flow Characteristics of Low Pressure Exhaust Hood Under Off-Design Conditions for Steam Turbines

In this paper, numerical investigations on the aerodynamic characteristics of the last three stages and the exhaust hood for a large power steam turbine were conducted under a series of mass flow conditions (100% ∼ 10% of the design condition) using the commercial CFD software ANSYS-CFX. The single passages of the last three stages and the whole exhaust hood are combined together as the computational domain. The main objective of this present work is to analyze the aerodynamic performance and the flow behavior of the exhaust hood. The variations of the static pressure recovery coefficient and the total pressure loss coefficient while the mass flow rate decreasing were analyzed. The static pressure distributions along the diffuser surface under different flow conditions were illustrated. The development of the vortex near the outlet of the diffuser was demonstrated through the velocity vector distribution at the meridional plane of the exhaust hood. The windage conditions were analyzed under 20% and 10% mass flow rate of the design condition. In addition, the back flow phenomenon was observed when the mass flow rate was below 50% of the design condition, and it starts from the hub region of the last stage rotor and grows up along the radial direction. The back flow also induces a sharp turning on the span-wise distribution of the angle θ (defined in Fig. 9) at the outlet of the last stage rotor. The three-dimensional streamlines inside the exhaust hood under different mass flow conditions were also compared.

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Numerical Study on the Main Coolant Pump of Sodium-Cooled Fast Reactor

Volume 1A: Symposia, Part 2 ◽

10.1115/ajkfluids2015-02403 ◽

2015 ◽

Author(s):

Sungho Ko ◽

Yeon-tae Kim

Keyword(s):

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Fast Reactor ◽

Numerical Study ◽

Pressure Rise ◽

Head Loss ◽

Computational Domain ◽

Coolant Pump ◽

Pump Head

A numerical study was conducted to predict the performance curve of a downscaled model of the main coolant pump for a sodium-cooled fast reactor and to reduce the head loss by the optimization of the diffuser blade. The ANSYS CFX program was utilized to obtain flow characteristics inside the pump as well as the overall pressure rise across the pump operating on- and off-design points. Computational domain was divided into several blocks to achieve high grid quality effectively and 7.5 million nodes were used totally to resolve small leakage flows as well as the flow inside the rotating impeller. The corresponding experiment was conducted to validate CFD computed results. The comparison between the CFD and experimental data shows excellent agreement in terms of mass flow rate and head rise on and near design operating points. The DOE (design of experiments) and RSM (response surface method)[1] were utilized to reduce the head loss by the diffuser blade in the pump. The diffuser blade was defined as four geometric parameters for DOE. The analysis of 25 cases was made to solve the output parameters for all design points which are defined by the DOE. RSM was fitting the output parameter as a function of the input parameters using regression analysis techniques. The optimized model increased the total pump head on the design point and the low mass flow rate point, but total pump head on 130% of operating mass flow rate was reduced than the initial model.

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Seed Cotton Mass Flow Measurement in the Gin

Applied Engineering in Agriculture ◽

10.13031/aea.12647 ◽

2018 ◽

Vol 34 (3) ◽

pp. 535-541

Author(s):

Robert G. Hardin IV

Keyword(s):

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Flow Measurement ◽

Static Pressure ◽

Seed Cotton ◽

Rotary Valve ◽

Air Velocity ◽

Second Stage ◽

Air Density

Abstract. Seed cotton mass flow measurement is necessary for the development of improved gin process control systems that can increase gin efficiency and improve fiber quality. Previous studies led to the development of a seed cotton mass flow rate sensor based on the static pressure drop across the blowbox, which primarily results from acceleration of the seed cotton. The initial sensor did not perform satisfactorily in a gin, and modifications were made to account for air leakage through the rotary valve at the blowbox and the temperature drop occurring due to heat exchange between the seed cotton and air. Mass flow rate was predicted based on the static pressure differences across the blowbox and rotary valve, the air velocity and density at the blowbox inlet, the air density in the blowbox, and the ambient air density. The first- and second-stage seed cotton cleaning and drying systems of the commercial-scale gin at the Cotton Ginning Research Unit were instrumented to test the improved model. Air velocity, cultivar, dryer temperature, and seed cotton feed rate were varied to determine their effects on model accuracy. Mean absolute percentage errors in predicting mass flow rate were 3.89% and 2.85% for the first- and second-stage systems, respectively; however, dryer temperature had a significant effect on the regression coefficients. An additional regression parameter was added to the model to better estimate the average blowbox density, reducing the mean absolute percentage error to 2.5% for both systems and eliminating the effect of dryer temperature on the regression coefficients. Keywords: Cotton, Ginning, Mass flow, Pneumatic conveying, Pressure.

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Unsteady Interaction Between Annulus and Turbine Rim Seal Flows

Volume 8: Turbomachinery, Parts A, B, and C ◽

10.1115/gt2012-69089 ◽

2012 ◽

Cited By ~ 3

Author(s):

Martin Chilla ◽

Howard Hodson ◽

David Newman

Keyword(s):

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Gas Turbines ◽

Measurement Data ◽

Design Flow ◽

Flow Conditions ◽

Disc Space ◽

Flow Interaction ◽

The Impact

In core gas turbines relatively cold air is purged through the hub gap between stator and rotor in order to seal the disc space against flow ingestion from the main annulus. Although the sealing mass flow rate is commonly very small compared to the main annulus mass flow rate, it can have significant effects on the development of the passage endwall flows and on the overall loss generation. In this paper, the interaction between annulus and rim sealing flows is investigated using numerical simulations of a generic high-pressure turbine. At first, the numerical approach is validated by comparing the results of calculations to measurement data at the design flow conditions. Following that, results from steady and unsteady calculations are used to describe in detail the aerodynamics in overlap-type rim seals and their effects on the blade passage flow. It is found that the flow interaction at the rim seal interface is strongly influenced by the velocity deficit of the rim sealing flow relative to the annulus flow as well as by the circumferentially non-uniform pressure field imposed by the rotor blades. At typical sealing flow conditions, the flow interaction is found to be naturally unsteady, with periodical vortex shedding into the rotor passage. Finally, the influence of the specific rim seal shape on the flow unsteadiness at the rim seal interface is investigated and the impact on turbine performance is assessed.

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Transient response of laminar premixed flame to a radially diverging/converging flow

10.32920/14636262.v1 ◽

2021 ◽

Author(s):

Meysam Sahafzadeh ◽

Larry W. Kostiuk ◽

Seth B. Dworkin

Keyword(s):

Mass Flow Rate ◽

Transient Response ◽

Mass Flow ◽

Flow Rate ◽

Laminar Flame ◽

Premixed Flames ◽

Scalar Fields ◽

Premixed Flame ◽

Computational Domain ◽

Tangential Strain

Laminar flamelets are often used to model premixed turbulent combustion. The libraries of rates of conversion from chemical to thermal enthalpies used for flamelets are typically based on counter-flow, stained laminar planar flames under steady conditions. The current research seeks further understanding of the effect of stretch on premixed flames by considering laminar flame dynamics in a cylindrically-symmetric outward radial flow geometry (i.e., inwardly propagating flame). This numerical model was designed to study the flame response when the flow and scalar fields align (i.e., no tangential strain on the flame) while the flame either expands (positive stretch) or contracts (negative stretch, which is a case that has been seldom explored) radially. The transient response of a laminar premixed flame has been investigated by applying a sinusoidal variation of mass flow rate at the inlet boundary with different frequencies to compare key characteristics of a steady unstretched flame to the dynamics of an unsteady stretched flame. An energy index (EI), which is the integration of the source term in the energy equation over all control volumes in the computational domain, was selected for the comparison. The transient response of laminar premixed flames, when subjected to positive and negative stretch, results in amplitude decrease and phase shift increase with increasing frequency. Other characteristics, such as the deviation of the EI at the mean mass flow rate between when the flame is expanding and contracting, are nonmonotonic with frequency. Also, the response of fuel lean flames is more sensitive to the frequency of the periodic stretching compared to a stoichiometric flame. An analysis to seek universality of transient flame responses across lean methane-air flames of different equivalence ratios (i.e., 1.0 to 0.7) using Damköhler Numbers (i.e., the ratio of a flow to chemical time scales) had limited success.

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Numerical Investigations on the Aerodynamic Performance of Last Stage – Exhaust Hood for Steam Turbines

ASME 2011 Power Conference, Volume 1 ◽

10.1115/power2011-55344 ◽

2011 ◽

Author(s):

Rui Yang ◽

Jiandao Yang ◽

Zeying Peng ◽

Liqun Shi ◽

Aping He ◽

...

Keyword(s):

Working Conditions ◽

Static Pressure ◽

Aerodynamic Performance ◽

Pressure Recovery ◽

Computational Domain ◽

Steam Turbines ◽

Exhaust Hood ◽

Recovery Coefficient ◽

Last Stage ◽

Pressure Recovery Coefficient

The aerodynamic performance and internal flow characteristics of the last stage and exhaust hood for steam turbines is numerically investigated using the Reynolds-Averaged Navier-Stokes (RANS) solutions based on the commercial CFD software ANSYS CFX. The full last stage including 66 stator blades and 64 rotor blades coupling with the exhaust hood is selected as the computational domain. The aerodynamic performance of last stage and static pressure recovery coefficient of exhaust hood at five different working conditions is conducted. The interaction between the last stage and exhaust hood is considered in this work. The effects of the non-uniform aerodynamic parameters along the rotor blade span on the static pressure recovery coefficient of the non-symmetric geometry of the exhaust hood are studied. The numerical results show that the efficiency of the last stage has the similar values ranges from 89.8% to 92.6% at different working conditions. In addition, the similar static pressure recovery coefficient of the exhaust hood was observed at five working conditions. The excellent aerodynamic performance of the exhaust hood was illustrated in this work.

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The response of the solid fuel ramjet combustor to the inflow excitations

Proceedings of the Institution of Mechanical Engineers Part G Journal of Aerospace Engineering ◽

10.1177/09544100211053405 ◽

2021 ◽

pp. 095441002110534

Author(s):

AmirMahdi Tahsini ◽

Seyed Saeid Nabavi

Keyword(s):

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Solid Fuel ◽

Ambient Pressure ◽

Excitation Frequency ◽

Engine Performance ◽

Computational Domain ◽

Rocket Motors ◽

Fuel Mass

The response of the solid fuel ramjet to the imposed excitations of the ambient pressure is investigated using full part computation of the system including the intake, combustion chamber, and exhaust nozzle. The finite volume solver of the turbulent reacting compressible flow is used to simulate the flow field, where two grid blocks are considered for discretizing the computational domain. Both impulsive and oscillatory excitations are imposed to predict the response of the solid fuel mass flow rate. The results demonstrate that strong fuel flow overshoot occurs in the case of sudden impulsive excitation which is omitted for gradual impulsive excitations. In addition, the oscillatory excitations eventually lead to regular oscillatory response with frequencies similar to the imposed excitations and decrease the average fuel mass flow rate independent of the excitation frequency. But the amplitude of the response depends on the excitation frequency and amplification occurs in some frequencies. This behavior is not related to the combustion instabilities and is similar to the L-star instability in the solid rocket motors. In the design and analysis of the solid fuel ramjets, the coupling of the flight dynamics and the engine performance must be considered, and this study is the first step of such complete methodology to have more accurate predictions.

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Design of an Optimized Inlet Shroud for a Flanged Diffuser

10.31224/osf.io/2qb6r ◽

2019 ◽

Author(s):

Dhruv Suri

Keyword(s):

Numerical Simulation ◽

Wind Turbine ◽

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Static Pressure ◽

Horizontal Axis Wind Turbine ◽

Ansys Fluent ◽

Modelling Techniques ◽

Flow Through

Numerical simulation using commercial CFD package ANSYS Fluent ® is carried out for a horizontal axis wind turbine with a flanged diffuser. An optimized inlet shape that further accelerates the flow through the diffuser has been proposed and evaluated. The principle behind the increase in mass flow rate due to the shape of the inlet shroud has been discussed, with emphasis on the modelling techniques presented. The low static pressure aft of the flange at the exit periphery induces a greater mass flow through the diffuser, thereby resulting in a higher capacity factor of the enclosed wind turbine. A comparison between different inlet shroud configurations has also been presented.

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Exergetic Evaluation of Steel Coaxial Heat Exchangers

10.21203/rs.3.rs-153774/v1 ◽

2021 ◽

Author(s):

Tobias Blanke ◽

Markus Hagenkamp ◽

Bernd Döring ◽

Joachim Göttsche ◽

Vitali Reger ◽

...

Keyword(s):

Reynolds Number ◽

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Reynolds Numbers ◽

Circular Ring ◽

High Mass ◽

Flow Conditions ◽

Hydraulic Losses ◽

Pipe Radius

Abstract Background: A proven option to found buildings are geothermally activated steel pipes. Statics determine their dimensions. Energy improvement research focuses on the radius of inner pipe of such coaxial geothermal probes. Mass flow rate is often constant when optimizing inner pipe dimensions. In contrast, in this study flow conditions in outer pipe are constant (constant Reynolds number) to ensure that they not change during optimization. Aim is to maximize net exergy difference for the desired flow type by changing inner pipe radius (after deduction of hydraulic effort). System technology can be selected based on this optimal design and its associated boundary conditions for mass flow and temperatures.Methods: Thermal calculations based on Hellström are carried out to quantify an influence of changing inner pipe radius on thermal yield. A hydraulic optimization of inner pipe radius is performed. Increasing inner pipe radius results in decreasing hydraulic losses in inner pipe but increases hydraulic losses in outer circular ring. Net exergy difference is a key performance indicator to combine thermal and hydraulic effects. Optimization of net exergy difference is carried out for selected scenarios. All calculations are based on various, but fixed Reynolds numbers in the circular ring (Re = [4e3; 1e4; 1e5]), instead of fixed mass flow rates. This ensures fixed flow conditions and no unnecessary high mass flow rate.Results: Optimal inner radius is approximately as large as outer radius considering thermal results. Reynolds numbers are always bigger in inner pipe, due to the constant Reynolds number in circular ring. Both indicate that from a thermal point of view, a high mass flow rate and a high degree of turbulence are particularly important. Hydraulic optimal inner pipe radius is 54% of outer pipe radius for laminar flow scenarios and 60% for turbulent flow scenarios. Exergetic optimization shows a predominant influence of hydraulic losses, especially for small temperature gains.Conclusions: Design of coaxial geothermal probes should focus on the hydraulic optimum and take energetic optimum as a secondary criterion to maximize net exergy difference.

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Parametric Modelling of a Spiral Bevel Gear Using CFD

Volume 1: Aircraft Engine; Ceramics; Coal, Biomass and Alternative Fuels; Education; Electric Power; Manufacturing Materials and Metallurgy ◽

10.1115/gt2010-22632 ◽

2010 ◽

Cited By ~ 1

Author(s):

Thomas Webb ◽

Carol Eastwick ◽

Herve´ Morvan

Keyword(s):

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Power Loss ◽

Static Pressure ◽

Bevel Gear ◽

Spiral Bevel Gear ◽

Parametric Modelling ◽

Number Of Teeth ◽

Spiral Bevel

Initial results investigating windage power loss on a rotating shrouded spiral bevel gear using a parametric solid model and Computational Fluid Dynamics (CFD) are presented. The context behind this study is a desire to use CFD as a tool to investigate heat-to-oil within gas turbine bearing chambers and gearboxes in order to reduce costly rig-based experiments. This paper contains the methodology for creation of the parametric model of a spiral bevel gear in Pro/Engineer, formulation of a mesh in ICEM CFD and the subsequent CFD analysis in Fluent 6.2.26 and 12.0.16. A single tooth segment of a 91 teethed spiral bevel gear is produced with periodic boundaries imposed to reduce computational cost. Validation against experimental results for a single control gear is shown with particularly good correlation between static pressure rise across the face of the gear. Mesh verification is also presented. Using the model to change the module of the gear (effectively the number of teeth), investigations show that windage power loss reduces when the number of teeth increases. Analysis of the static pressure variation throughout the domain shows that all gears tested exhibit a linearly increasing relationship between non-dimensional mass-flow-rate and the pressure drop through the shroud restriction. The control gear was seen to have only a weak increase in static pressure gain across the gear tooth as the mass-flow-rate increases; however, a far larger increase exists for the module cases tested — at comparable mass-flow-rates to the control gear. As the number of teeth increase, the pressure gain across the gear reduces, and vice-versa. It is this difference between the gears that results in dissimilar windage power losses.

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