Numerical Techniques Applied to Hydraulic Turbines: A Perspective Review

2016 ◽  
Vol 68 (1) ◽  
Author(s):  
Chirag Trivedi ◽  
Michel J. Cervantes ◽  
Ole Gunnar Dahlhaug
Keyword(s):  
Steady State ◽  
Numerical Models ◽  
Guide Vane ◽  
Numerical Technique ◽  
Fluid Dynamic ◽  
Operating Conditions ◽  
Experimental Investigations ◽  
Numerical Techniques ◽  
Transient Conditions ◽  
Hydraulic Turbines

Applications of computational fluid dynamic (CFD) techniques to hydropower have increased rapidly in the last three decades. The majority of the experimental investigations of hydraulic turbines were supported by numerical studies and this has become a standard practice. In the paper, applied numerical techniques and flow modeling approaches to simulate the hydraulic turbines are discussed. Both steady-state and transient operating conditions of the turbines are considered for the review. The steady-state conditions include the best efficiency point (BEP), high load (HL), and part load (PL). The transient conditions include load variation, startup, shutdown, and total load rejection. The performance of the applied numerical models and turbulence modeling with respect to the operating conditions are discussed. The recently developed numerical technique (transient blade row modeling) using the Fourier transformation (FT) method is discussed. This technique allows guide vane and blade passages to be modeled with the pitch ratio other than unity. Numerical modeling and simulation of hydraulic turbines during the transient operating conditions is one of the most challenging tasks because guide vanes' angular movement is time-dependent and mesh should be dynamic/moving. Different approaches applied to simulate the transient conditions and their limitations are discussed. Overall, this review summarizes the role of numerical techniques, advantages, limitations, and upcoming challenges within hydropower.

A Systematic Validation of a Francis Turbine Under Design and Off-Design Loads

2019 ◽  
Vol 4 (1) ◽  
Author(s):  
Chirag Trivedi
Keyword(s):  
Numerical Model ◽  
Power Efficiency ◽  
Numerical Models ◽  
Fluid Dynamic ◽  
Total Error ◽  
Operating Conditions ◽  
Francis Turbine ◽  
Local Pressure ◽  
Hydraulic Turbines ◽  
Reliable Design

Computational fluid dynamic (CFD) techniques have played a significant role in improving the efficiency of the hydraulic turbines. To achieve safe and reliable design, numerical results should be trustworthy and free from any suspicion. Proper verification and validation (V&V) are vital to obtain credible results. In this work, first we present verification of a numerical model, Francis turbine, using different approaches to ensure minimum discretization errors and proper convergence. Then, we present detailed validation of the numerical model. Two operating conditions, best efficiency point (BEP) (100% load) and part load (67.2% load), are selected for the study. Turbine head, power, efficiency, and local pressure are used for validation. The pressure data are validated in time- and frequency-domains at sensitive locations in the turbine. We also investigated the different boundary conditions, turbulence intensity, and time-steps. The results showed that, while assessing the convergence history, convergence of local pressure/velocity in the turbine is important in addition to the mass and momentum parameters. Furthermore, error in hydraulic efficiency can be misleading, and effort should make to determine the errors in torque, head, and flow rate separately. The total error is 9.82% at critical locations in the turbine. The paper describes a customized V&V approach for the turbines that will help users to determine total error and to establish credibility of numerical models within hydraulic turbines.

Assessment of Scale Resolved CFD Methods for the Investigation of Lean Burn Spray Flames

2016 ◽  
Author(s):  
A. Andreini ◽  
D. Bertini ◽  
L. Mazzei ◽  
S. Puggelli
Keyword(s):  
Steady State ◽  
Numerical Models ◽  
Combustion Model ◽  
Experimental Investigations ◽  
Strong Impact ◽  
Lean Burn ◽  
Two Phase ◽  
Spray Flames ◽  
Flamelet Generated Manifold ◽  
Reactive Processes

Incoming standards on NOx emissions are motivating many aero-engines manufacturers to adopt the lean burn combustion concept. However, several technological issues have to be faced in this transition, among which limited availability of air for cooling purpose and thermoacoustics phenomena that should be managed to safely implement this burning mode. In this scenario, standard numerical design tools are not often capable of characterizing such devices. Thus, considering also the difficulties of experimental investigations in a highly pressurized and reactive environment, unsteady scale resolved CFD methods are required to correctly understand the combustor performances. In the last years Large Eddy (LES) and hybrid RANS-LES models such as Scale Adaptive Simulations (SAS) have undergone considerable developments. Such approaches have been already applied for gaseous flames, leading to a strong enhancement in phenomena prediction with respect to standard steady-state simulations. However, huge research efforts are still required when spray flames are considered, since all the numerical models chosen to describe spray dynamics and the related reactive processes can have a strong impact on the accuracy of the whole simulation. In this work a set of scale resolved simulations have been carried out on the DLR Generic Single Sector Combustor spray flame for which measurements both in non-reactive and reactive test conditions are available. Exploiting a two-phase Eulerian-Lagrangian approach combined with a Flamelet Generated Manifold (FGM) combustion model, LES simulations have been performed in order to assess the potential improvements with respect to steady state solutions. Additional comparisons have also been accomplished with SAS calculations based on Eddy Dissipation combustion model (EDM). The comparison with experimental results shows that the chosen unsteady strategies lead to a more physical description of reactive processes with respect to RANS simulations. FGM model showed some limitations in reproducing the partially-premixed nature of the flame, whereas SAS-EDM proved to be a robust modelling strategy within an industrial perspective. A new set of spray boundary conditions for liquid injection is also proposed whose realiability is proved through a detailed comparison against experimental data.

Multiphysics Analysis of Thorium-Based Fuel Performance Under Reactor Steady-State and Transient Accident

2020 ◽  
Author(s):  
Chenjie Qiu ◽  
Rong Liu ◽  
Wenzhong Zhou
Keyword(s):  
Steady State ◽  
Safety Margin ◽  
Operating Conditions ◽  
Fuel Performance ◽  
Transient Conditions ◽  
Normal Operating ◽  
Accident Conditions ◽  
Behavior Models ◽  
Line Temperature ◽  
Thermal Physical Properties

Abstract The ThO2 fuel has higher thermal conductivity and melting boiling point than the UO2 fuel, which is beneficial to the fast removal of heat and the improvement of fuel melt margin. In this paper, the material properties and thermodynamic behaviors of thorium-based fuel were firstly reviewed. And then the thermal physical properties and the fuel behavior models of Th0.923U0.077O2 fuel and Th0.923Pu0.077O2 fuel have been implemented in fuel performance analysis code FRAPCON and FRAPTRAN. Finally, the performances of Th0.923U0.077O2 fuel, Th0.923Pu0.077O2 fuel and UO2 fuel under both normal operating conditions and transient conditions (RIA and LOCA) are analyzed and compared. The Th0.923U0.077O2 fuel is found to have lower fuel center-line temperature and the thorium-based fuels are observed to have a delayed pellet-cladding mechanical interaction (PCMI) under steady state. Furthermore, the fission gas release, cladding strain and internal fuel energy under transient conditions are found to be lower too. Lastly, the cladding displacement and temperature under transient conditions are also compared. The thorium-based fuel was found to have a higher safety margin and accident resistance than conventional UO2 fuel under both normal operating conditions and accident conditions.

scholarly journals Proposal of a new simplified fluid dynamic model for aerospace servovalves

2019 ◽  
Vol 304 ◽  
pp. 04014
Author(s):  
Matteo D.L. Dalla Vedova ◽  
Pier Carlo Berri
Keyword(s):  
Numerical Model ◽  
Flight Control ◽  
Numerical Models ◽  
Fluid Dynamic ◽  
Computational Effort ◽  
Operating Conditions ◽  
System Level ◽  
Simplified Models ◽  
System Level Simulation ◽  
Detailed Computer

Highly detailed computer models are required for design and development of modern flight control systems, capable of emulating with high accuracy the behaviour of on-board equipment. At the same time, different simplified models are needed, specifically intended for operations such as the optimization of preliminary design and the development of diagnostic or prognostic strategies. These simplified models are required to combine sufficient levels of accuracy and reliability with reduced computational costs, to minimize the computational burden associated with prognostic and optimization algorithms. In this work, we focus on electro-hydraulic actuators, since they are critical subsystems in terms of safety and availability of the aircraft. Advanced monitoring and prognostic algorithms require new numerical models, combining an acceptable computational effort with a satisfying ability to simulate their performance and dynamics. To this purpose, this paper proposes a new simplified numerical model of the servovalve fluid-dynamic behaviour. This numerical algorithm, based on a very compact semi-empirical formulation, is intended to take into account in a simplified but sufficiently accurate way several typical effects related to the SV spool geometry and the operating conditions. To evaluate the approximations introduced by this model into a system-level simulation, it has been integrated into a dedicated numerical model simulating a simple electrohydraulic on-board actuator, and compared with a higher fidelity servovalve model.

Approximating EHL Film Thickness Profiles Under Transient Conditions

2002 ◽  
Vol 124 (3) ◽  
pp. 443-447 ◽  
Author(s):  
S. Messe´ ◽  
A. A. Lubrecht
Keyword(s):  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Analytical Approximation ◽  
Industrial Applications ◽  
Operating Conditions ◽  
Numerical Techniques ◽  
Transient Conditions ◽  
Entrainment Velocity ◽  
Thickness Profile ◽  
Ehl Contact

In ElastoHydrodynamic Lubrication (EHL), transient processes are much more common than stationary ones. Predicting the film thickness under steady state conditions has become straight forward. Using numerical methods, the effect of transient conditions on the film thickness profile can be computed. However, those analyses are very time consuming even using advanced numerical techniques. As such, they are inadequate for industrial applications as design and development. This paper shows that under certain assumptions, an approximate formula of the transient film thickness profile can be derived under transient operating conditions. The variations can occur in the geometry, the load or the hydrodynamic velocity. The theory can handle all variations separately, or even a combination of several parameters varying simultaneously. The analytical approximation obtained is rather good apart from the constriction at the contact edge(s). This approach can be applied to any set of time dependent conditions (load, speed, geometry). As an example an EHL contact is studied in which reversal of the entrainment velocity occurs.

A Numerical Investigation on the Influence of Porosity on the Steady-State and Transient Thermal–Hydraulic Behavior of the PBMR

2016 ◽  
Vol 138 (10) ◽  
Author(s):  
Masoumeh Sadat Latifi ◽  
Saeed Setayeshi ◽  
Giuseppe Starace ◽  
Maria Fiorentino
Keyword(s):  
Thermal Conductivity ◽  
Steady State ◽  
Effective Thermal Conductivity ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Heat Removal ◽  
Coolant Temperature ◽  
Pebble Bed ◽  
Transient Conditions ◽  
Decay Heat

The thermal–hydraulic phenomena in a pebble bed modular reactor (PBMR) core have been simulated under steady-state and transient conditions. The PBMR core is basically a long right circular cylinder with a fuel effective height of 11 m and a diameter of 3.7 m. It contains approximately 452,000 fuel pebbles. A three-dimensional computational fluid dynamic (CFD) model of the PBMR core has been developed to study the influence of porosity on the core performance after reactor shutdown. The developed model was carried out on a personal computer using ANSYS fluent 14.5. Several important heat transfer and fluid flow parameters have been examined under steady-state and transient conditions, including the coolant temperature, effective thermal conductivity of the pebble bed, and the decay heat. Porosity was found to have a significant influence on the coolant temperature, on the effective thermal conductivity of the pebble bed, on the decay heat, and on the required time for heat removal.

scholarly journals A new simplified fluid dynamic model for digital twins of electrohydraulic servovalves

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Matteo Davide Lorenzo Dalla Vedova ◽  
Pier Carlo Berri
Keyword(s):  
Fluid Dynamics ◽  
Dynamic Models ◽  
Numerical Models ◽  
Fluid Dynamic ◽  
Water Hammer ◽  
Operating Conditions ◽  
Nonlinear Dependence ◽  
Content Type ◽  
Digital Twins ◽  
Proposed Model

Purpose The purpose of this paper is to propose a new simplified numerical model, based on a very compact semi-empirical formulation, able to simulate the fluid dynamics behaviors of an electrohydraulic servovalve taking into account several effects due to valve geometry (e.g. flow leakage between spool and sleeve) and operating conditions (e.g. variable supply pressure or water hammer). Design/methodology/approach The proposed model simulates the valve performance through a simplified representation, deriving from the linearized approach based on pressure and flow gains, but able to evaluate the mutual interaction between boundary conditions, pressure saturation and leak assessment. Its performance was evaluated comparing with other fluid dynamics numerical models (a detailed physics-based high-fidelity one and other simplified models available in the literature). Findings Although still showing some limitations attributable to its simplified formulation, the proposed model overcomes several deficiencies typical of the most common fluid dynamic models available in the literature, describing the water hammer and the nonlinear dependence of the delivery differential pressure with the spool displacement. Originality/value Although still based on a simplified formulation with reduced computational costs, the proposed model introduces a new nonlinear approach that, approximating with suitable precision the pressure-flow fluid dynamic characteristic of a servovalve, overcomes the shortcomings typical of such models.

scholarly journals Thermal behavior analysis of PWR fuel during RIA at various fuel burnups using modified theatre code

2016 ◽  
Vol 31 (4) ◽  
pp. 307-317
Author(s):  
Amjad Nawaz ◽  
Yoshikawa Hidekazu ◽  
Ming Yang ◽  
Anwar Hussain
Keyword(s):  
Steady State ◽  
Thermal Performance ◽  
Pulse Width ◽  
Pulse Height ◽  
Operating Conditions ◽  
Reactor Safety ◽  
Transient Conditions ◽  
Power Pulse ◽  
Fuel Rod ◽  
Fuel Failure

The fuel irradiation and burnup causes geometrical and dimensional changes in the fuel rod which affects its thermal resistance and ultimately affects the fuel rod behavior during steady-state and transient conditions. The consistent analysis of fuel rod thermal performance is essential for precise evaluation of reactor safety in operational transients and accidents. In this work, analysis of PWR fuel rod thermal performance is carried out under steady-state and transient conditions at different fuel burnups. The analysis is performed by using thermal hydraulic code, THEATRe. The code is modified by adding burnup dependent fuel rod behavior models. The original code uses as-fabricated fuel rod dimensions during steady-state and transient conditions which can be modified to perform more consistent reactor safety analysis. AP1000 reactor is considered as a reference reactor for this analysis. The effect of burnup on steady-state fuel rod parameters has been investigated. For transient analysis, hypothetical reactivity initiated accident was simulated by considering a triangular power pulse of variable pulse height (relative to the full power reactor operating conditions) and pulse width at different fuel burnups which corresponds to fresh fuel, low and medium burnup fuels. The effect of power pulse height, pulse width and fuel burnup on fuel rod temperatures has been investigated. The results of reactivity initiated accident analysis show that the fuel failure mechanisms are different for fresh fuel and fuel at different burnup levels. The fuel failure in fresh fuel is expected due to fuel melting as fuel temperature increases with increase in pulse energy (pulse height). However, at relatively higher burnups, the fuel failure is expected due to cladding failure caused by strong pellet clad mechanical interaction, where, the contact pressure increases beyond the cladding yield strength.

ANALISIS KECEPATAN AIR MASUK TERHADAP BUKAAN GUIDE VANE TURBIN CROSSFLOW SKALA PICO HYDRO DENGAN SIMULASI CFD

2021 ◽  
Vol 3 (3) ◽  
pp. 94-101
Author(s):  
Dimas Riadi ◽  
Remon Lapisa ◽  
Hendri Nurdin ◽  
Mulianti Mulianti
Keyword(s):  
Steady State ◽  
Computational Fluid Dynamic ◽  
Guide Vane ◽  
Fluid Dynamic ◽  
Cross Flow

Turbin Ossberger atau yang biasa dikenal dengan turbin Cross-flow adalah type turbin bertekanan yang kerap dipakai pada PLTA. Contohnya adalah pembangkit listrik tenaga pico hydro. Kenagarian Koto Hilalang di Kabupaten Solok Kecamatan Kubung, Sumatera Barat merupakan salah satu contoh lokasi dimana Pembangkit Listrik Tenaga pico hydro dapat digunakan sebagai sumber tenaga. Penelitian ini dilakukan untuk menganalisis akibat dari variasi guide vane pada turbin jenis cross-flow yang dimanfaatkan sebagai pembangkit listrik tenaga pico hydro dengan daya yang dihasilkan sebesar 31,85 Kw. Dengan adanya penelitian ini dapat menentukan kecepatan magnitude air terhadap variasi bukaan guide vane untuk meningkatkan efisiensi turbin. Metode dalam pelaksanaan penelitian ini yaitu simulasi Computational Fluid Dynamic (CFD) dilakukan pada perangkat lunak Autodesk CFD dengan model turbulens k-ipsilon. Tahapan dalam melaksanakan simulasi CFD ini yakni dengan memvariasikan bukaan guide vane dengan variasi 25%, 50%, 75%, 100%. Hasil analisis pada simulasi CFD menunjukan bahwa kecepatan maksimal berada pada bukaan 25% yang menghasilkan kecepatan masuk sebesar 112,79 m/s pada parametric distance 32, simulasi ini menunjukan kecepatan masuk air mengalami penurunan. Kecepatan masuk air pada simulasi ini di buat tetap dengan sebesar 11,72 m/s dan dalam keadaan steady state.

Aerodynamic Improvement of a Transonic Fan Outlet Guide Vane Using 3D Design Optimization

2011 ◽  
Author(s):  
Giles Endicott ◽  
Toyotaka Sonoda ◽  
Markus Olhofer ◽  
Toshiyuki Arima
Keyword(s):  
Cfd Simulation ◽  
Experimental Testing ◽  
Guide Vane ◽  
Numerical Technique ◽  
Boundary Layer Separation ◽  
Operating Conditions ◽  
Free Form ◽  
Optimized Design ◽  
3D Design ◽  
Transonic Fan

In this paper we follow the process of rapid design improvement for the fan outlet guide vane for a turbofan powering a very light jet. The small size of such engines leads to a low Reynolds number, resulting in flow-fields prone to boundary layer separation, causing significant losses in efficiency. This paper studies experimental testing in a scale rig, and numerical simulation using CFD, leading to the comparison of the two datasets and hence assessment of the numerical technique. The mesh employed by the CFD simulation was modified using Free Form Deformation to create different geometric designs, and hence an optimization scheme was subsequently utilized to find the deformation of 28 variables which maximized aerodynamic performance. The final optimized design displayed a novel oscillatory casing profile, while the blade shape had increased camber relative to the baseline. The improvement in pressure loss was approximately 20% across the range of operating conditions studied.

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