• Journal of the Korea Society for Simulation
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• v.14 no.2
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• pp.35-43
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• 2005

Feedwater heaters of many nuclear power plants have recently experienced wall thinning damage, which will increase as operating time progresses. As it is judged that the wall thinning damages have generated due to local fluid behavior around the impingement baffle installed in downstream of the high pressure turbine extraction steam line to avoid colliding directly with the tubes, numerical analyses using PHOENICS code were performed for two models with original clogged impingement baffle and modified multi-hole impingement baffle. To identify the relation between wall thinning and fluid behavior, the local velocity components in x-, y-, and z-directions based on the numerical analysis for the model with the clogged impingement baffle were compared with the wall thickness data by ultrasonic test. From the comparison of the numerical analysis results and the wall thickness data, the local velocity component only in the y-direction, and not in the x- and z-direction, was analogous to the wall thinning configuration. From the result of the numerical analysis for the modified impingement baffle to mitigate the shell wall thinning, it was identified that the shell wall thinning may be controlled by the reduction of the local velocity in the y-direction.

• Journal of ILASS-Korea
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• v.2 no.1
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• pp.36-45
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• 1997

A spray-wall impingement model for fuel sprays is proposed and implemented as a module into the KIVA-POSTECH code. The model is based on the single droplet experiments. The droplet behaviors after impingement are determined from experimental correlations. Different behaviors of impinged droplets depend on the wall temperature and the critical temperature of the fuel. Fuel film formation is taken into account so that the model can be applicable to any wall temperature and injection conditions. Computational results on a normal and on inclined wall are in good agreement for the spray shape and penetration. More validation against experiments and development of the heat transfer model are needed for further improvement.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.4
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• pp.124-131
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• 2007

The numerical study on behavior of impinging spray from high-pressure swirl injector under various ambient temperatures was performed by using spray vaporization model and spray-wall impingement model implemented in modified KIVA code, and these spray models were estimated by comparison with experimental results. To compute the spray-wall impingement process, the Gosman model, which is based on the droplet behavior after impingement determined by experimental correlations, was used. The modified Abramzon and Sirignano model, that includes the effects of variable thermodynamic properties and non-unitary Lewis number in the gas film, was adapted for spray vaporization process. The exciplex fluorescence measurements were also conducted for comparison. The experimental and numerical analysis were carried out at the ambient pressures of 0.1 MPa and at the ambient temperature of 293 K and 473 K, and the spray characteristics, such as spray-wall impingement process, gas velocity field, SMD and vapor concentration, were acquired. It was found that the impinging spray develops active and SMD is small at vaporization conditions.

• Journal of Mechanical Science and Technology
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• v.15 no.7
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• pp.951-961
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• 2001

The present article presents an extension to the computational model for spray/wall interaction and liquid film processes that has been dealt with in the earlier studies (Lee and Ryou, 2000a). The extensions incorporate film spread due to impingement forces and dynamic motion induced by film inertia to predict the dynamic characteristics of wall films effectively. The film model includes the impingement pressure of droplets, tangential momentum transfer due to the impinging droplets on the film surface and the gas shear force at the film surface. Validation of the spray/wall interaction model and the film model was carried out for non-evaporative diesel sprays against several sources of experimental data. The computational model for spray/wall interactions was in good agreement with experimental data for both spray radius and height. The film model in the present work was better than the previous static film model, indicating that the dynamic effects of film motion should be considered for wall films. On the overall the present film model was acceptable for predication of the film radius and thickness.

• Journal of Mechanical Science and Technology
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• v.14 no.7
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• pp.796-806
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• 2000

To understand the transient behavior of droplets after impingement in a diesel engine, a numerical model for diesel sprays impinging on a flat wall is newly developed by the proposition of several mathematical formulae to determine the post-impingement characteristics of droplets. The new model consists of three representative regimes such as rebound, deposition and splash. The gas phase is modeled in terms of the Eulerian conservation equations, and the dispersed phase is calculated using a discrete droplet model. To validate the new model, the calculated results are compared with several experimental data. The results show that the new model is generally in good agreement with the experimental data. Therefore, it is thought that the new model is acceptable for the prediction of transient behavior of wall sprays.

• Journal of computational fluids engineering
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• v.13 no.2
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• pp.68-72
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• 2008

NUFLEX is a general purpose thermo/fluid flow analysis program which has various physical models including spray. In NUFLEX, spray models are composed of breakup and collision models of droplet. However, in case of diesel engine, interaction between wall-film and impingement model considering heat transfer is not coded in NUFLEX. In this study, Lee & Ryou impingement & wall-film model considering heat transfer is applied to NUFLEX. For the verification of this NUFLEX program, numerical results are compared with experimental data. Differences of film thickness and radius between numerical results and experimental data are within 10% error range. The results show that NUFLEX can be used for comprehensive analysis of spray phenomena.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.2
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• pp.187-194
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• 2001

Spray impingement and fuel film formation models were developed and incorporated into the computational fluid dynamics code. STAR-CD. The spray/wall interaction process was modeled by considering the change of behaviour with surface temperature conditions and the fuel film formation. We divided the behaviour of fuel droplets after impingement into rebound, spread and splash using the Weber number and the parameter K. The Spray impingement model accounts for mass conservation, energy conservation and heat transfer to the impinging droplets. The fuel film formation model was developed by integrating the continuity, Navier-Stokes and energy equations along the direction of fuel film thickness. Validation of the models was conducted using previous diesel spray experimental data and the present experimental results for the gasoline spray impingement. In all the cases, the prediction compared reasonably well with the experimental results. The spray impingement and fuel film formation models have been applied to the spray/wall impingement in high speed direct injection diesel engines.

• Journal of Mechanical Science and Technology
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• v.15 no.3
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• pp.374-383
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• 2001

The spray/wall interaction is considered as an important phenomenon influencing air-fuel mixing in the internal combustion engines. In order to adequately represent the spray/wall interaction process, impingement regimes and post-impingement behavior have been modeled using experimental data and conservation constraints. The modeled regimes were stick, rebound, spread and splash. The tangential velocities of splashing droplets were obtained using a theoretical relationship. The continuous phase was modeled using the Eulerian conservation equations, and the dispersed phase was calculated using a discrete droplet model. The numerical simulations were compared to experimental results for spray impingement normal to the wall. The predictions for the secondary droplet velocities and droplet sizes were in good agreement with the experimental data.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.919-924
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• 2000

Spray impingement model and fuel film formation model were developed and incorporated into the computational fluid dynamics code, STAR-CD. The spray/wall interaction process were modelled by considering the change of behaviour with surface temperature condition and fuel film formation. We divided behaviour of fuel droplets after impingement into stick, rebound and splash using Weber number and parameter K. Spray impingement model accounts for mass conservation, energy conservation and heat transfer to the impinging droplets. A fuel film formation model was developed by Integrating the continuity, the Navier-Stokes and the energy equations along the direction of fuel film thickness. The validation of the model was conducted using diesel spray experimental data and gasoline spray impingement experiment. In all cases, the prediction compared reasonably well with experimental results. Spray impingement model and fuel film formation model have been applied to a direct injection diesel engine combustion chamber.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.5
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• pp.45-57
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• 2002

In this paper, the results gained by applying many impingement models to the cylinder and flat plate were analyzed in comparison with the experimental data to study a spray/wall interaction phenomena. To begin with, the behavior of spray injected normal to the wall was analysed using three different impingement models ; Naber and Reitz model(NR model), Watkins and Wang model(WW model) and Park and Watkins model(PW model) in the present calculation. The results obtained from these models were compared with experimental data of Katsura et. al. The results indicated that PW model was in better agreement with experimental data than the NR and WW model. Also f3r spray injected at 30DEG , the result of three models were compared with experimental data of Fujimoto et. al. The results showed that m model overpredicted the penetration in the radial direction because this model was based on the inviscid jet analogy. WW model did not predicted the radius and height of the wall spray effectively. It might be thought that this discrepancy was due to the lack of consideration of spray film velocity occurred at impingement site. The result of PW model agrees with the experimental data as time goes on. In particular, a height of the spray droplets was predicted more closely to the experimental data than the other two models. The results of PW model in which the spray droplets were distributed densely around the edge of droplet distribution shaped in a circle had an agreement with the experimental data of Fujimoto et. al. Therefore, it was concluded that PW model performed better than M and WW model for prediction of spray behavior. The numerical calculation using PW model performed to the cylinder similar to the real shape of DI engine. The results showed that vortex strength near the wall in the cylinder was stronger than that in the case of flat plate. Contrary to the flat plat, an existence of the side wall in the cylinder caused the tangential velocity component to be reduced and the normal velocity component to be increased. The flow tends to rotate to the inside of cylinder going upward to the right side wall of cylinder gradually as time passes. Also, the results showed that as the spray angle increases, the gas velocity distribution and the tumble flow seemed to be formed widely.