In-house CFD Research Articles

Numerical and experimental study of fluid flow in simplified blade cascade with prescribed harmonic motion

In this paper, a numerical simulation and experimental measurements of compressible viscous fluid flow in simplified blade cascade are compared. The cascade consists of five flat plates three of which perform prescribed harmonic motion. The computed unsteady velocity field is compared with experimental measurements at selected points. Moreover, the power spectral density corresponding to the frequency of harmonic motion is computed for both the numerical and experimental data and compared. The numerical simulation was performed using the developed in-house CFD software based on the discontinuous Galerkin method, which offers high order of accuracy.

Numerical simulation of fluid flow through simplified blade cascade with prescribed harmonic motion using discontinuous Galerkin method

This paper deals with a numerical simulation of compressible viscous fluid flow around three flat plates with prescribed harmonic motion. This arrangement presents a simplified blade cascade with forward wave motion. The aim of this simulation is to determine the aerodynamic forces acting on the flat plates. The mathematical model describing this problem is formed by Favre-averaged system of Navier-Stokes equations in arbitrary Lagrangian-Eulerian (ALE) formulation completed by one-equation Spalart-Allmaras turbulence model. The simulation was performed using the developed in-house CFD software based on discontinuous Galerkin method, which offers high order of accuracy.

Numerical and experimental study of fluid flow in simplified blade cascade with prescribed harmonic motion

In this paper, a numerical simulation and experimental measurements of compressible viscous fluid flow in simplified blade cascade are compared. The cascade consists of five flat plates three of which perform prescribed harmonic motion. The computed unsteady velocity field is compared with experimental measurements at selected points. Moreover, the power spectral density corresponding to the frequency of harmonic motion is computed for both the numerical and experimental data and compared. The numerical simulation was performed using the developed in-house CFD software based on the discontinuous Galerkin method, which offers high order of accuracy.

Magneto-hydrodynamic Marangoni flow in bottom-heated lid-driven cavity

The paper presents fluid and heat flow in an open square cavity where the free, forced and Marangoni convection are taking place simultaneously in presence of external magnetic field. Free convection induces from bottom heating, whereas forced convection is imposed by the motion of two sidewalls. Thermal interaction through open surface at top is also taken into account invoking Marangoni convection. The development of thermal-hydraulic flow physics is addressed systematically through both transient and steady analyses using an in-house CFD code. The results reveal the distinct flow-patterns using the pertinent parameters like Marangoni number (Ma=0–1000), Biot number (Bi=0–10), Reynolds number (Re=10–500), Richardson number (Ri=0.1–100) and Hartmann number (Ha=0–100). The impact of the mutual strengths of three convection modes on a liquid metal (Pr=0.054) in the presence of uniform magnetic field is explored exhaustively to extract the useful data relevant for practical applications. The thermal mixing behavior of the liquid is also assessed. The novelty of this work is it addresses magneto-hydrodynamic (MHD) flow that couples with simultaneous Marangoni, free and forced convection, as first time.

Study of the wet steam flow in the blade tip rotor linear blade cascade

Experimental investigations of non-equilibrium spontaneous condensation in transonic steam flows in a linear blade cascade were carried out. The cascade consists of the rotor blades of the low-pressure (LP) steam turbine last stage. The experimental testing facility is a part of a small-scale steam power plant located at the Silesian University of Technology in Gliwice. The steam parameters at the testing facility inlet correspond to the wet steam conditions in a low-pressure steam turbine. Static pressure measurements on the blade surface as well as Schlieren images were used to assess the flow field in the steam turbine rotor tip blade linear cascade for different flow conditions. The experimental results were used to validate an in-house CFD code.

Performance Evaluation of Nose Cap to Silica Tile Joint of RLV-TD under the Simulated Flight Environment using Plasma Wind Tunnel Facility

Indian Space Research Organisation, India has successfully flight tested the reusable launch vehicle through launching of a demonstration flight known as RLV-TD HEX mission. This mission has given a platform for exposing the thermal protection system to the real hypersonic flight thermal conditions and thereby validated the design. In this vehicle, the nose cap region is thermally protected by carbon–carbon followed by silica tiles with a gap in between them for thermal expansion. The gap is filled with silica fibre. Base material on which the C–C is placed is made of molybdenum. Silica tile with strain isolation pad is bonded to aluminium structure. These interfaces with a variety of materials are characterised with different coefficients of thermal expansion joined together. In order to evaluate and qualify this joint, model tests were carried out in Plasma Wind Tunnel facility under the simultaneous simulation of heat flux and shear levels as expected in flight. The thermal and flow parameters around the model are determined and made available for the thermal analysis using in-house CFD code. Two tests were carried out. The measured temperatures at different locations were benign in both these tests and the SiC coating on C–C and the interface were also intact. These tests essentially qualified the joint interface between C–C and molybdenum bracket and C–C to silica tile interface of RLV-TD.

Integrated transient simulation of a BFB boiler with CFD models for the BFB furnace and dynamic system models for the steam cycle and boiler operation

An approach for integrated transient simulation of a BFB boiler furnace and the coupled steam cycle is presented. The BFB furnace is simulated with in-house CFD models implemented in the ANSYS Fluent® software. The boiler steam cycle with control loops is simulated with the dynamic process simulation software Apros®. The paper describes the steps taken to couple the modeling tools and discusses the way the numerical solutions can proceed in unison. The approach is demonstrated for a commercial BFB boiler. A fast load change situation was selected as the test case. A coupled transient simulation was carried out and the process behavior during the transient was analyzed. Critical properties affecting the feasibility of a given ramp rate are the emission release rates and temperature transients in the boiler. These properties are monitored during the transient simulation. The paper presents these results along with instantaneous data that show the spatial distribution of temperature and gas composition in the furnace. The paper shows that the modeling approach is feasible. Applicability of the approach and possible future improvements are discussed.

Towards a thorough Validation of Simulation Tools for CO2 Pipeline Transport

In this work the Schlumberger flow assurance tool OLGA and SINTEF Energy Research in-house CFD tool are assessed for their ability to describe depressurization behaviour of CO2 pipelines. For this purpose, three full-bore experimental depressurization tests with pure CO2 have been performed at the Statoil's R&D center in Trondheim, Norway.Simulations results are in general agreement with the experiments with the exception of the behaviour at the innermost position of the where OLGA predicts significantly lower temperatures, and SINTEF tool over-estimate the temperature. Both models predict liquid dry-out time with an error of a few seconds.The simulation results are sensitive to the pipe outer heat transfer coefficient, used between the pipe surface and the ambient humid air. Reduction of the uncertainty in the heat-flux to the pipe is identified as a key factor for further validation.

Liquid phase evaporation on the normal shock wave in moist air transonic flows in nozzles

This paper presents a numerical analysis of the atmospheric air transonic flow through de Laval nozzles. By nature, atmospheric air always contains a certain amount of water vapor. The calculations were made using a Laval nozzle with a high expansion rate and a convergent-divergent (CD) “half-nozzle”, referred to as a transonic diffuser, with a much slower expansion rate. The calculations were performed using an in-house CFD code. The computational model made it possible to simulate the formation of the liquid phase due to spontaneous condensation of water vapor contained in moist air. The transonic flow calculations also take account of the presence of a normal shock wave in the nozzle supersonic part to analyze the effect of the liquid phase evaporation.

Effects of non-equilibrium condensation on aerodynamics of the flow field in a steam turbine cascade

In the present paper an in-house CFD code is developed using Roe scheme to simulate condensing two-phase flow in blade to blade passage of a steam turbine. Effects of condensation on the flow field of steam turbine rotor tip section are investigated for different outlet pressures. Firstly, comparison is performed between results of wet and dry cases. Then effects of outlet pressure variations on the flow field are studied. Finally effects of condensation on different specifications of the flow field (total pressure loss coefficient, entropy generation and deviation angle) are investigated. Also the mechanism of flow deviation in the cascade flow field is described. Condensation has a great influence on the behavior of the flow field based on the numerical results of this paper. It changes the outflow direction and consequently the flow entering to the next blade deviates from its on-design condition, thus additional losses are produced. For example, the value of deviation angle reaches to 7.62for wet case and exit Mach number Me=1.45. Also there are stagnation pressure loss and entropy generation due to non-equilibrium condensation that reduce the efficiency of the steam turbine

Benchmark computations of wave run-up on single cylinder and four cylinders by naoe-FOAM-SJTU solver

The benchmark simulations of wave run-up on a fixed single truncated circular cylinder and four circular cylinders are presented in this paper. Our in-house CFD solver naoe-FOAM-SJTU is adopted which is an unsteady two-phase CFD code based on the open source package OpenFOAM. The Navier-Stokes equations are employed as the governing equations, and the volume of fluid (VOF) method is applied for capturing the free surface. Monochromatic incident waves with the specified wave period and wave height are simulated and wave run-up heights around the cylinder are computed and recorded with numerical virtual wave probes. The relationship between the wave run-up heights and the incident wave parameters are analyzed. The numerical results indicate that the presented naoe-FOAM-SJTU solver can provide accurate predictions for the wave run-up on one fixed cylinder and four cylinders, which has been proved by the comparison of simulated results with experimental data.

CFD simulation of a pilot plant delayed coking reactor using an in-house CFD code

espanolRESUMEN Una simulacion de un reactor piloto de coquizacion retardada fue realizada empleando un codigo propio de dinamica de fluidos computacional (CFD). El reactor fue modelado como un sistema dinamico de tres fases donde el coque es una fase solida porosa, el fondo de vacio es la fase liquida y los productos destilables son la fase gaseosa. Los balances de continuidad, momento y energia propuestos para describir la dinamica del proceso de coquizacion fueron discretizados mediante el metodo de los volumenes finitos sobre una malla axisimetrica de dos dimensiones. Un algoritmo tipo PEA fue desarrollado para describir el arrastre entre las fases fluidas y un algoritmo SIMPLEC modificado llevo a cabo el acoplamiento entre la presion y la velocidad. El simulador de CFD fue programado en lenguaje C++ para sistema operativo tipo Linux; todos los graficos fueron construidos en la plataforma de visualizacion Paraview. Una corrida completa de 12 horas y el posterior enfriamiento de la cama de coque obtenida para tres fondos de vacio fue simulada, los resultados fueron comparados con datos experimentales y un buen acuerdo fue encontrado, el simulador demostro gran potencial para ser escalado a nivel industrial. EnglishABSTRACT A simulation of a pilot plant delayed coking reactor was performed using an in-house computational fluid dynamics (CFD) code. The reactor was modeled as a three-phase dynamic system where the coke is the porous solid phase, the vacuum residue the liquid phase and the distillable product the gas phase. Equations of continuity, momentum, and energy proposed to describe the coking dynamic process where discretized employing the finite volume method and the domain was defined by a 2D structured axisymmetric grid. A PEA algorithm was developed to account for the drag between the fluid phases, and a modified SIMPLEC algorithm achieved the pressure-velocity coupling. The CFD simulator was programmed in C++ code for Linux operating system; all the graphics were constructed in ParaView visualization platform. A full run of 12 hours and the cooling of the resulting coke bed for three different vacuum residues were simulated, the results were compared with experimental data and a good agreement was observed, the simulator demonstrated great potential to be scaled up to industrial level. portuguesRESUMO Foi realizada uma simulacao de uma planta piloto de um reator de coqueamento retardado aplicando um codigo interno de fluidodinâmica computacional (CFD). O reator foi modelado como um sistema dinâmico de tres fases, estando o coque em fase solida, o residuo de vacuo em fase liquida, e os destilaveis em fase gasosa. As equacoes de continuidade, de momento e de energia propostas para descrever o processo de coquemento dinâmico foram discretizadas utilizando o metodo dos volumes finitos, e a area foi definida por uma grade de eixo de simetria estruturada em 2D. Foi desenvolvido um algoritmo PEA para representar o arrasto entre as fases fluidas, e um algoritmo SIMPLEC modificado atingiu o acoplamento pressao-velocidade. O simulador CFD foi programado em codigo C++ para o sistema operacional Linux. Todos os graficos foram construidos em uma plataforma ParaView. Simulando a operacao de 12 horas e o arrefecimento do leito de coque resultante para tres residuos de vacuo diferentes, os resultados foram comparados com os dados experimentais e foi observado uma boa correlacao, o simulador mostrou grande potencial de ser escalado no nivel industrial.

CFD simulation of water vapor absorption in laminar falling film solution of water-LiBr ─ Drop and jet modes

The rate of absorbed water vapor over a horizontal tube bank in a water-cooled falling film absorber depends on several parameters and working conditions. The flow regime between the tubes in falling film absorbers is one of the most influential parameters in the amount of the absorbed vapor. Among different falling film regimes, in this study, the drop and jet modes are simulated numerically. The full Navier-Stokes equations are solved and the well-known volume of fluid (VOF) method is used to capture the gas/liquid interface. In addition, the energy and diffusion equations are solved in this 3D-simulation with aid of an in-house CFD code. Adaptive mesh refinement, in accordance with the magnitude of volume fraction gradient, has strongly improved the interface capturing and therefore increased the accuracy of simulation. The simulation results reveal that by changing just the regime from drops to jets, the rate of average vapor mass flux decreases one order of magnitude, from 6.3×10-3 to 4.76×10-4kg s-1m-2.

Modelling of Blood Flow in Stenosed Arteries

Stenosis means narrowing arteries. This abnormality in arteries is perturb the flow field. In this work, the flow pattern in the various shape of stenosed artery (50–90% cross-section area reduction) are reported. An in-house CFD solver is used for simulation of blood flow. The code is validated. Post-validation, velocity and pressure contours reported for various shape of stenosis. The result shows that the blockage disturbed the flow and it is responsible for developing high wall shear stress on the wall. 90% blockage in an artery can be extremely dangerous because of flow become transient and turbulent flow.

Steady state operation simulation of the Francis-99 turbine by means of advanced turbulence models

The paper presents numerical simulation of the flow in hydraulic turbine based on the experimental data of the II Francis-99 workshop. The calculation domain includes the wicket gate, runner and draft tube with rotating reference frame for the runner zone. Different turbulence models such as k-ω SST, ζ-f and RSM were considered. The calculations were performed by means of in-house CFD code SigmaFlow. The numerical simulation for part load, high load and best efficiency operation points were performed.

Numerical study of falling film absorption process in a vertical tube absorber including Soret and Dufour effects

Vapor absorption in aqueous LiBr inside a vertical tube absorber is studied numerically. The governing equations of concentration and energy have been derived in general forms, including the species interdiffusion, Soret and Dufour effects due to combined concentration and temperature gradients during absorption process. All thermophysical properties of solution and the heat of absorption are variable, as functions of temperature and concentration in constant absorber pressure. An in-house CFD code is used to solve the governing equations. The obtained results have been validated with available experimental data and a good agreement is observed. The simulation results reveal the important role of the interdiffusion term in energy equation. Moreover, the Soret and Dufour effects result in a relatively small increase in average heat and mass fluxes at the interface.

Performance modeling and optimization of parallel LU-SGS on many-core processors for 3D high-order CFD simulations

As a typical Gauss---Seidel method, the inherent strong data dependency of lower-upper symmetric Gauss---Seidel (LU-SGS) poses tough challenges for shared-memory parallelization. On early multi-core processors, the pipelined parallel LU-SGS approach achieves promising scalability. However, on emerging many-core processors such as Xeon Phi, experience from our in-house high-order CFD program show that the parallel efficiency drops dramatically to less than 25%. In this paper, we model and analyze the performance of the pipelined parallel LU-SGS algorithm, present a two-level pipeline (TL-Pipeline) approach using nested OpenMP to further exploit fine-grained parallelisms and mitigate the parallel performance bottlenecks. Our TL-Pipeline approach achieves 20% performance gains for a regular problem $$(256\times 256\times 256)$$(256×256×256) on Xeon Phi. We also discuss some practical problems including domain decomposition and algorithm parameters tuning for realistic CFD simulations. Generally, our work is applicable to the shared-memory parallelization of all Gauss---Seidel like methods with intrinsic strong data dependency.

Verification of transport equations in a general purpose commercial CFD code.

In this paper, the Verification and Validation methodology is presented. This method aims to increase the reliability and the trust that can be placed into complex CFD simulations. The first step of this methodology, the code verification is presented in greater details. The CFD transport equations in steady state, transient and Arbitrary Eulerian Lagrangian (ALE, used for transient moving mesh) formulations in Ansys CFX are verified. It is shown that the expected spatial and temporal order of convergence are achieved for the steady state and the transient formulations. Unfortunately this is not completely the case for the ALE formulation. As for a lot of other commercial and in-house CFD codes, the temporal convergence of the velocity is limited to a first order where a second order would have been expected.

CFD-based shape optimization of steam turbine blade cascade in transonic two phase flows

In this study CFD-based shape optimization of a 3D nozzle and a 2D turbine blade cascade is undertaken in the presence of non-equilibrium condensation within the considered flow channels. A two-fluid formulation is used for the simulation of unsteady, turbulent, supersonic and compressible flow of wet steam accounting for relevant phase interaction between nucleated liquid droplets and continuous vapor phase. An in-house CFD code is developed to solve the governing equations of the two phase flow and was validated against available experimental data. Optimization is carried out in respect to various objective functions. It is shown that nucleation rate and maximum droplet radius are the best suited target functions for reducing thermodynamic and aerodynamic losses caused by the spontaneous nucleation. The maximum increase of 2.1% in turbine blade efficiency is achieved through shape optimization process.

A novel technique for heat transfer enhancement from a horizontal heated pipe by using nanofluid restrained flow

In this paper, a numerical investigation using an in-house CFD code written in FORTRAN is carried out for an effective cooling of a horizontal heated pipe. The study focuses on the heat transfer enhancement by using nanofluid as a cooling medium comprising CuO nanoparticles and water as a base fluid. Moreover, a confined circular jacket surrounds the heated pipe with axial slot inlet and outlet ports. Via the circular jacket, the eccentricity between the heated pipe and the circular jacket centers is implemented as a control key for the heat transfer rate. Also, the circular jacket enables the nanofluid to be in direct contact with the hot pipe. Cold nanofluid exchange heat by both forced and natural convection (mixed convection). The presented study is performed for two mixed convection cases, assisting and opposing. The Grashof number is fixed at 104 while the Richardson number is varied in the range of 0.01–100 via the Reynolds number of the nanofluid. The CuO solid volume fraction has been varied from 0 to 0.05 while the eccentricity ratio has been changed from −0.5 (downward direction) to 0.5 (upward direction). Through the study, the radius ratio is kept constant at 2. The numerical solution was compared with previous work, and good agreement was found. It was also found that the assisting flow enhanced the rate of heat transfer when compared to the opposing flow. Moreover, the nanoparticles have a positive effect on the rate of heat transfer over the entire range of Richardson number; however, for natural convection domain (Ri>10), the nanoparticles concentration should be extensively increased in order to enhance the heat transfer rate.