scholarly journals Experimental study of water hammer pressure surge

2019 ◽  
Author(s):  
C. Bombardieri ◽  
T. Traudt ◽  
C. Manfletti
Keyword(s):  
Fluid Dynamic ◽  
Pressure Profile ◽  
Propulsion System ◽  
Flash Evaporation ◽  
Two Phase ◽  
Priming Process ◽  
Test Elements ◽  
Pressure Peak ◽  
Pipe Geometry ◽  
Tank Pressure

During the start-up of the propulsion system of a satellite or spacecraft, the opening of the tank isolation valve will cause the propellant to flow into an evacuated feedline and slam against a closed thruster valve. This filling process, called priming, can cause severe pressure peaks that could lead to structural failure. In the case of monopropellants such as hydrazine, also, the risk of adiabatic compression detonation must be taken into account in the design of the feedline subsystem. The phenomenon of priming involves complex two-phase flow: the liquid entering the evacuated pipe undergoes flash evaporation creating a vapor cushion in front of the liquid that mixes with the residual inert gas in the line. Moreover, the dissolved pressurizing gas in the liquid will desorb making the priming process difficult to model. In order to study this phenomenon, a new test-bench has been built at DLR Lampoldshausen which allows fluid transient experiments in the same conditions as the operating space system. Tests are performed with water and ethanol at different conditions (tank pressure, vacuum level, pressurizing gas helium vs. nitrogen, etc.). The effect of the geometry is also investigated, comparing different test-elements such as straight, tees, and elbow pipes. The pressure profile is found to be dependent on the geometry and on the downstream conditions. The acoustic wave reflection caused by the pipe geometry and fluid dynamic effects such as the aforementioned desorption and flash evaporation induce a complex pressure profile of the first pressure peak. Finally, numerical simulations of the priming process are performed by means of EcosimPro software in conjunction with European Space Propulsion System Simulation (ESPSS) libraries and results are compared with experiments.

Computational Fluid Dynamic Applications for Jet Propulsion System Integration

1991 ◽  
Vol 113 (1) ◽  
pp. 40-50 ◽  
Author(s):  
R. H. Tindell
Keyword(s):  
System Integration ◽  
Fluid Dynamic ◽  
Low Cost ◽  
Separated Flow ◽  
Propulsion System ◽  
Navier Stokes ◽  
Aerospace Vehicles ◽  
Design Engineers ◽  
Flow Phenomena ◽  
The Impact

The impact of computational fluid dynamics (CFD) methods on the development of advanced aerospace vehicles is growing stronger year by year. Design engineers are now becoming familiar with CFD tools and are developing productive methods and techniques for their applications. This paper presents and discusses applications of CFD methods used at Grumman to design and predict the performance of propulsion system elements such as inlets and nozzles. The paper demonstrates techniques for applying various CFD codes and shows several interesting and unique results. A novel application of a supersonic Euler analysis of an inlet approach flow field, to clarify a wind tunnel-to-flight data conflict, is presented. In another example, calculations and measurements of low-speed inlet performance at angle of attack are compared. This is highlighted by employing a simplistic and low-cost computational model. More complex inlet flow phenomena at high angles of attack, calculated using an approach that combines a panel method with a Navier-Stokes (N-S) code, is also reviewed. The inlet fluid mechanics picture is rounded out by describing an N-S calculation and a comparison with test data of an offset diffuser having massively separated flow on one wall. Finally, the propulsion integration picture is completed by a discussion of the results of nozzle-afterbody calculations, using both a complete aircraft simulation in a N-S code, and a more economical calculation using an equivalent body of revolution technique.

Eulerian Two-Phase Flow Modeling of Steam Direct Contact Condensation for the Fukushima Accident Investigation

2014 ◽  
Author(s):  
Marco Pellegrini ◽  
Giulia Agostinelli ◽  
Hidetoshi Okada ◽  
Masanori Naitoh
Keyword(s):  
Two Phase Flow ◽  
Volume Fraction ◽  
Fluid Model ◽  
Fluid Dynamic ◽  
Interfacial Region ◽  
Phase Flow ◽  
Two Phase ◽  
Fukushima Accident ◽  
Average Cell Size ◽  
Average Cell

Steam condensation is characterized by a relatively large interfacial region between gas and liquid which, in computational fluid dynamic (CFD) analyses, allows the creation of a discretized domain whose average cell size is larger than the interface itself. For this reason generally one fluid model with interface tracking (e.g. volume of fluid method, VOF) is employed for its solution in CFD, since the solution of the interface requires a reasonable amount of cells, reducing the modeling efforts. However, for some particular condensation applications, requiring the computation of long transients or the steam ejected through a large number of holes, one-fluid model becomes computationally too expensive for providing engineering information, and a two-fluid model (i.e. Eulerian two-phase flow) is preferable. Eulerian two-phase flow requires the introduction of closure terms representing the interactions between the two fluids in particular, in the condensation case, drag and heat transfer. Both terms involve the description of the interaction area whose definition is different from the typical one adopted in the boiling analyses. In the present work a simple but effective formulation for the interaction area is given based on the volume fraction gradient and then applied to a validation test case of steam bubbling in various subcooling conditions. It has been shown that this method gives realistic values of bubble detachment time, bubble penetration for the cases of interest in the nuclear application and in the particular application to the Fukushima Daiichi accident.

Measurement of Flow-Induced Forces: A Single Flexible Tube in a Rigid Triangular-Pitch Bundle Subjected to Two-Phase Cross-Flow

2015 ◽  
Author(s):  
Enrico Deri ◽  
Joël Nibas ◽  
Olivier Ries ◽  
André Adobes
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Tube Bundle ◽  
Fluid Dynamic ◽  
Cross Flow ◽  
Maintenance Policy ◽  
Excitation Spectra ◽  
Two Phase ◽  
Force Coefficients ◽  
Out Of Plane

Flow-induced vibrations of Steam Generator tube bundles are a major concern for the operators of nuclear power plants. In order to predict damages due to such vibrations, EDF has developed the numerical tool GeViBus, which allows one to asses risk and thereafter to optimize the SG maintenance policy. The software is based on a semi analytical model of fluid-dynamic forces and dimensionless fluid force coefficients which need to be assessed by experiment. The database of dimensionless coefficients is updated in order to cover all existing tube bundle configurations. Within this framework, a new test rig was presented in a previous conference with the aim of assessing parallel triangular tube arrangement submitted to a two-phase cross-flow. This paper presents the result of the first phase of the associated experiments in terms of force coefficients and two-phase flow excitation spectra for both in-plane and out-of-plane vibration.

scholarly journals Grid convergence study of a cyclone separator using different mesh structures

2017 ◽  
Vol 23 (3) ◽  
pp. 311-320 ◽  
Author(s):  
R.A.F. Oliveira ◽  
G.H. Justi ◽  
G.C. Lopes
Keyword(s):  
Pressure Drop ◽  
Collection Efficiency ◽  
Fluid Dynamic ◽  
Two Phase ◽  
Mesh Structure ◽  
Pressure Drops ◽  
Regular Elements ◽  
Grid Convergence ◽  
Grid Convergence Index ◽  
Mesh Structures

In a cyclone design, pressure drop and collection efficiency are two important performance parameters to estimate its implementation viability. The optimum design provides higher efficiencies and lower pressure drops. In this paper, a grid independence study was performed to determine the most appropriate mesh to simulate the two-phase flow in a Stairmand cyclone. Computational fluid dynamic (CFD) tools were used to simulate the flow in an Eulerian-Lagrangian approach. Two different mesh structure, one with wall-refinement and the other with regular elements, and several mesh sizes were tested. The grid convergence index (GCI) method was applied to evaluate the result independence. The CFD model results were compared with empirical correlations from bibliography, showing good agreement. The wall-refined mesh with 287 thousand elements obtained errors of 9.8% for collection efficiency and 14.2% for pressure drop, while the same mesh, with regular elements, obtained errors of 8.7% for collection efficiency and 0.01% for pressure drop.

CFD Prediction of the Effects of Surface Roughness on Elastohydrodynamic Lubrication under Rolling/Sliding Conditions

2012 ◽  
Vol 184-185 ◽  
pp. 86-89 ◽  
Author(s):  
Shian Gao ◽  
Sutthinan Srirattayawong
Keyword(s):  
Surface Roughness ◽  
Shear Stress ◽  
Fluid Dynamic ◽  
Flow Behavior ◽  
Elastohydrodynamic Lubrication ◽  
Pressure Profile ◽  
Hertzian Contact ◽  
Pure Rolling ◽  
Large Fluctuations ◽  
Two Parameters

The surface roughness plays an important role in elastohydrodynamic lubrication (EHL). To improve the lubrication system the flow behavior and lubrication mechanism must be understood, especially in the thin film classification. The effects of surface roughness in the EHL problem are complicated and difficult to measure by experiment. Therefore numerical simulation using the computational fluid dynamic (CFD) approach is proposed in this research. The CFD model developed has taken the arbitrary surface roughness into consideration, and has been used to predict the characteristics of fluid flow, such as the pressure distribution, the minimal film thickness and the shear stress. The cylinder is considered to be under elastic deformation according to the theory of Hertzian contact and the surface of cylinder is defined to have an arbitrary roughness. The simulation results show that the surface roughness has significant effects on the pressure profile and shear stress, especially in the case of pure rolling, where the two parameters in the rough surface case show large fluctuations that are much higher than the corresponding smooth surface case.

Determination of Pressure Profile During Closed-Vessel Test Through Computational Fluid Dynamics Simulation

2015 ◽  
Vol 8 (2) ◽  
Author(s):  
Ahmed Bougamra ◽  
Huilin Lu
Keyword(s):  
Solid Propellant ◽  
Time History ◽  
Initial Pressure ◽  
Pressure Profile ◽  
Dynamics Simulation ◽  
Solid Propellants ◽  
Closed Vessel ◽  
Governing Equations ◽  
Two Phase ◽  
Closed Chamber

Two-phase flow modeling of solid propellants has great potential for simulating and predicting the ballistic parameters in closed-vessel tests as well as in guns. This paper presents a numerical model describing the combustion of a solid propellant in a closed chamber and takes into account what happens in such two-phase, unsteady, reactive-flow systems. The governing equations were derived in the form of coupled, nonlinear axisymmetric partial differential equations. The governing equations with customized parameters were implemented into ansys fluent 14.5. The presented solutions predict the pressure profile inside the closed chamber. The results show that the present code adequately predicts the pressure–time history. The numerical results are in agreement with the experiment. Some discussions are given regarding the effect of the grain shape and the sensitivity of these predictions to the initial pressure of the solid propellant bed. The study demonstrated the capability of using the present model implemented into Fluent, to simulate the combustion of solid propellants in a closed vessel and, eventually, the interior ballistic process in guns.

Computational and Experimental Investigation of the Vertical Flash Tank Separator Part 1: Effect of Parameters on Separation Efficiency

2019 ◽  
Vol 27 (01) ◽  
pp. 1950005 ◽  
Author(s):  
Raid Ahmed Mahmood ◽  
David Buttsworth ◽  
Ray Malpress
Keyword(s):  
Separation Efficiency ◽  
Fluid Dynamic ◽  
Effective Area ◽  
Working Fluid ◽  
Cfd Simulations ◽  
Liquid Separation ◽  
Two Phase ◽  
Flash Tank ◽  
Tank Design ◽  
The Heat Transfer Coefficient

The flash tank separator is one of the most important components that can be used to improve the performance of a refrigeration cycle by separating the liquid from the gas–liquid two-phase flow and providing the evaporator with only liquid refrigerant. This technique increases the effective area and enhances the heat transfer coefficient in the evaporator. To optimize the size of the vertical flash tank separator for obtaining high separation efficiency, the effect of the size of the vertical flash tank separator needs to be considered. This paper investigates the effect of the size on the liquid separation efficiency of the vertical flash tank separator. This paper also assesses the usefulness of Computational Fluid Dynamic (CFD) in flash tank design, and this is achieved through experiments and simulations on a range of relevant configurations using water as the working fluid. The results revealed that the size has a significant effect on the liquid separation efficiency, as the highest value was achieved by the largest size (VFT-V5). The CFD simulations give a good agreement with the experiments; all the simulations underestimated the liquid separation efficiency by approximately 0.02 over the range of conditions tested.

scholarly journals Numerical Study on the Gas-Water Two-Phase Flow in the Self-Priming Process of Self-Priming Centrifugal Pump

Processes ◽  
2019 ◽  
Vol 7 (6) ◽  
pp. 330 ◽  
Author(s):  
Chuan Wang ◽  
Bo Hu ◽  
Yong Zhu ◽  
Xiuli Wang ◽  
Can Luo ◽  
...  
Keyword(s):  
Centrifugal Pump ◽  
Two Phase Flow ◽  
Numerical Study ◽  
The Self ◽  
Main Stage ◽  
Phase Flow ◽  
Urban Greening ◽  
Two Phase ◽  
Ansys Cfx ◽  
Priming Process

A self-priming centrifugal pump can be used in various areas such as agricultural irrigation, urban greening, and building water-supply. In order to simulate the gas-water two-phase flow in the self-priming process of a self-priming centrifugal pump, the unsteady numerical calculation of a typical self-priming centrifugal pump was performed using the ANSYS Computational Fluid X (ANSYS CFX) software. It was found that the whole self-priming process of a self-priming pump can be divided into three stages: the initial self-priming stage, the middle self-priming stage, and the final self-priming stage. Moreover, the self-priming time of the initial and final self-priming stages accounts for a small percentage of the whole self-priming process, while the middle self-priming stage is the main stage in the self-priming process and further determines the length of the self-priming time.

scholarly journals Numerical simulation of modification of non-metallic inclusions by calcium treatment in the argon-stirred ladle

2019 ◽  
Vol 116 (5) ◽  
pp. 515
Author(s):  
Edgar Ivan Castro-Cedeno ◽  
Alain Jardy ◽  
Benjamin Boissiere ◽  
Jean Lehmann ◽  
Pascal Gardin ◽  
...  
Keyword(s):  
Flow Model ◽  
Fluid Dynamic ◽  
Steel Ladle ◽  
Local Concentration ◽  
Two Phase ◽  
Euler Flow ◽  
Metallic Inclusions ◽  
Dissolved Species ◽  
Secondary Steelmaking ◽  
Technological Challenge

Nowadays, depending on the steel grade, Ca treatment with the aim of modifying the morphology and melting temperature of non-metallic inclusions is performed in the secondary steelmaking process. The addition of calcium to steel melts rises a technological challenge because at steelmaking temperatures Ca has the tendency to vaporize from the ladle. Efforts are actively pursued in developing solutions that increase Ca yield and improve repeatability of results from treatment to treatment. This work presents a two-phase Euler-Euler flow model of a steel ladle with gas stirring through bottom porous plugs. The model considers that before gas exits through the ladle top, some Ca is transferred from the gas to the liquid steel. The yield is thus defined as the ratio between the Ca transferred to the steel and the total calcium injected into the ladle. The fluid-dynamic calculations are coupled with ArcelorMittal thermodynamic software CEQCSI to get the evolution of the local concentration of dissolved species and non-metallic inclusions assuming local thermodynamic equilibrium. Industrial trials have been performed at one of ArcelorMittal’s facilities with the aim of obtaining data to validate the model. Samples of steel were taken before, during, and after the Ca injection treatment. The total Ca content and the inclusion populations in the steel samples can be compared against the results given by the model, as well as the measured and calculated Ca yield.

Based on the Principle of Approximate Model Established Model Test Rig Simulation of the Actual Test Bench

2012 ◽  
Vol 614-615 ◽  
pp. 14-19
Author(s):  
Min Xue ◽  
Zhu Ma ◽  
Yan Jun Li ◽  
Long Bin Yang ◽  
Fang Zhu
Keyword(s):  
Wave Phenomenon ◽  
Fluid Dynamic ◽  
Pressure Fluctuations ◽  
Steam Pressure ◽  
Approximate Model ◽  
Two Phase ◽  
Small Model ◽  
Main Steam ◽  
Relationship Of ◽  
Physical Phenomena

For Marine pressurization boiler dynamic system, when the boiler provide steam for air storage, boiler drum pressure and steam pressure will have produced a wave phenomenon; In order to research this a wave phenomenon, considering similar principles , establish the model experiments to simulate the wave process. Due to boiler provide steam for air storage that involves in many complex physical processes, including two phase flow, heat transfer, braising physical phenomena. By a simple analysis, to be completely similar to the model, model must be the same as the real situation; it will lose the small model experimental significance. According to this problem, we consider use approximate modeling method which usually used in engineering, seize the pressure fluctuations of the main contradictions; Put forward in the process of considering only reflect pressure fluctuations of local fluid dynamic field project of similar approximation, Finally we get the fluctuation relationship of the actual conditions and small model experiment of main steam pressure.

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