WAHA Code - development of single phase code (original) (raw)
Related papers
Numerical scheme of the WAHA code
This paper describes the numerical scheme used in the WAHA code that was developed within the WAHALoads project for simulations of fast transients in 1D piping systems. Two-fluid model equations described in a companion paper entitled "Two-Fluid Model of the WAHA Code for Simulations of Water Hammer Transients," are solved with an operator splitting procedure: the non-conservative characteristic upwind scheme is used to solve the hyperbolic part of the equations with the non-relaxation source terms, while the relaxation source terms are treated in the second step of the operator splitting procedure. Water properties are calculated with a newly developed set of subroutines that use pretabulated water properties. Special models that were developed for treatment of the abrupt area changes and branches in the piping systems are described. Various test cases, which were used to test the accuracy of the basic numerical scheme and the accompanying numerical models, are described and discussed together with the typical results of simulations.
Two-Phase Flow Water Hammer Transients : Towards the WAHA Code
In view of developing and validating a new code aimed at predicting fast transient two-phase flows in NPPs, extensive experimental data sets are being collected by means of three test facilities in the WAHALoads project. The paper reports on the benchmark exercises which show the need for a specific code using advanced numerical methods, on the experiments which have been carried out, and on the main characteristics of the code itself.
WAHA Code - numerical method of WAHA code
The document gives an overview of the numerical method, which is used in the current version of the WAHA code and is planned to be used in the final version of the WAHA code. The described numerical scheme can be used with conservative, primitive, or with some other sets of basic variables. The final choice of the basic variables depends on the simulations of the smooth-area change flows that are currently tested. Another undetermined choice is a number of the basic equations, which depends on the chosen physical model. The most likely choice is the 6-eq. two-fluid model, however, if the assumption of the thermal equilibrium of the vapor phase is adopted, the 5-eq. two-fluid model will be used. Some minor details that are not clarified in the present version of the document (for example: treatment of very small vapor or liquid volume fractions) will be addressed in the next versions of the document.
Depressurization of Vertical Pipe with Temperature Gradient Modeled with WAHA Code
Science and Technology of Nuclear Installations, 2012
The subcooled decompression under temperature gradient experiment performed by Takeda and Toda in 1979 has been reproduced using the in-house code WAHA version 3. The sudden blowdown of a pressurized water pipe under temperature gradient generates a travelling pressure wave that changes from decompression to compression, and vice versa, every time it reaches the two-phase region near the orifice break. The pressure wave amplitude and frequency are obtained at different locations of the pipe's length. The value of the wave period during the first 20 ms of the experiment seems to be correct but the pressure amplitude is overpredicted. The main three parameters that contribute to the pressure wave behavior are: the break orifice (critical flow model), the ambient pressure at the outlet, and the number of volumes used for the calculation. Recent studies using RELAP5 code have reproduced the early pressure wave (transient) of the same experiment reducing the discharge coefficient and the bubble diameter. In the present paper, the long-term pipe pressure, that is, 2 seconds after rupture, is used to estimate the break orifice that originates the pressure wave. The numerical stability of the WAHA code is clearly proven with the results using different Courant numbers.
Flow models and numerical schemes for single/two-phase transient flow in one dimension
Applied Mathematical Modelling
In the two-phase flow field, a traditional mathematical model for simulating the transition of severe slugging flow presents a challenge when liquid slugs completely block pipelines. Accordingly, an advanced and practical slug model that is derived from a mixture model associated with a slip closure is essential to solving the problem in cooperation with the two-fluid model. The model can offset numerical instability that arises from the discontinuous function of the friction factor across the transition from one flow pattern to the other. Two numerical schemes, the non-iterative and the iterative, are developed, and the proposed schemes can stably predict the transient problems under the Courant-Friedrichs-Lewy (CFL) condition for semi-implicit/implicit schemes. In the present work, pressure transients produced by a complex phenomenon, named water hammer effect, are captured using the single-phase flow model in one-dimension to verify the applicability of the numerical schemes and the friction factor model. At last, the analysis of the two-phase transient flow in a pipeline-riser system indicates that the significant advantage of the present schemes is the robustness that the numerical prediction of the severe slugging behaviour is accurate and stable.
Transient simulation of two-phase flows in pipes
International Journal of Multiphase Flow, 1998
Transient simulation of two-phase gas-liquid flow in pipes requires considerable computational efforts. Until recently, most available commercial codes are based on the two-fluid model which includes one momentum conservation equation for each phase. However, in normal pipe flow operation, especially in oil and gas transport, the transient response of the system proves to be relatively slow. Thus it is reasonable
In this report, three reduced two phase flow models are presented. The first one is a totally conservative model implanted in EUROPLEXUS as SG2P. It generates strong pressure oscillations at the contact discontinuities, and it blows up numerically in some difficult cases. Then, two quasiconservative five-equation models are implanted as SGMP in EUROPLEXUS. The "Topology Transport Equation" in SGMP-Model 1 has no additional term. The mixture sound speed is calculated as "Frozen Sound Speed". The "Topology Transport Equation" in SGMP-Model 2 has an additional term to describe the interaction between the phases, which represents the compressibility of the phases. The associated mixture sound speed corresponds to the Wallis formula. All of these two models are successfully extended to multiphase case. Several tests are carried out. Both of these models can treat the interface between the fluids correctly. The SGMP-Model 1 is numerically more robust. However, when there are two coexisting phases, it cannot treat the mixture in a physically correct way. Thus, the SGMP-Model 2 should be chosen to simulate the fluids mixture. RESUME / CONCLUSIONS de niveau DO en cas de niveau confidentialité supérieur du document SO
Testing the numerical method for one-dimensional shock treatment
In the early 80's the SMUP computer code was developed at the "Jozef Stefan" Institute for simulation of two-phase flow in steam generators. It was suitable only for steady-state problems and was unable to simulate transient behaviour. In this paper, efforts are presented to find a suitable numerical method to renew the old SMUP computer code. The obsolete numerical code has to be replaced with a more efficient one that would be able to treat time-dependent problems. It also has to ensure accurate solution during shock propagations. One-dimensional shock propagations in a tube were studied at zero viscosity. To simplify the equation of state the ideal gas was chosen as a working fluid. Stability margins in the form of transport matrix eigenvalues were calculated. Results were found to be close to those already published.
International Journal of Multiphase Flow, 2008
The paper deals with the problem of the wall shear stress during rapid transient 1D flows in a piping system caused by water hammers in two-phase flow induced by a fast valve closure. The evolution of the transient wall shear stress is interpreted in terms of two steps. The first step is a sudden and dramatic change of the wall shear stress due to the passage of the pressure wave. The second step is a relaxation process of the shear stress which is modeled from the Extended Irreversible Thermodynamics theory. The friction relaxation model (FRM) presented in the first part of this paper describes both steps of the evolution of the wall shear stress during water hammers. The second part of the paper deals with the application of the FRM model as a closure law in the WAHA code. The main purpose of the WAHA code is to predict various situations relative to single-and two-phase water hammer transients in piping systems. The last part of the paper deals with the simulation of several cases from the UMSICHT databank using the adapted WAHA computer code with the FRM model. The results of these simulations are systematically compared with the experimental data. It is concluded that the new FRM model has a clear effect on water hammer pressure wave damping and on the pressure wave propagation velocity.
Energies
Subchannel codes have been widely used for thermal-hydraulics analyses in nuclear reactors. This paper details the development of a novel subchannel code within the Idaho National Laboratory’s (INL) Multi-physics Object Oriented Simulation Environment (MOOSE). MOOSE is a parallel computational framework targeted at the solution of systems of coupled, nonlinear partial differential equations, that often arise in the simulation of nuclear processes. As such, it includes codes/modules able to solve the multiple linear and nonlinear physics that describe a nuclear reactor, under normal operation conditions or accidents. This includes thermal-hydraulics, fuel performance, and neutronics codes, between others. A MOOSE-based subchannel code is a new addition to the fleet of INL-developed codes, based on the MOOSE framework. In this work, we present the derivation of the subchannel equations for a single-phase fluid, we proceed with the description of the algorithm that is used to solve the...