Crimped ribbon flame arresters are important safety devices in the chemical industry, especially for the danger- ous situations. Although proper design of arresters by the numerical simulation method is promising, its...Crimped ribbon flame arresters are important safety devices in the chemical industry, especially for the danger- ous situations. Although proper design of arresters by the numerical simulation method is promising, its reliabil- ity and accuracy are dependent upon the mathematical model. In this work, an integrated mathematical model for the microchannel in the crimped ribbon flame attesters was set up; the fluid flow behavior and the sensitiv- ities of four chemical kinetics mechanisms of propane-air on the accuracy were analysed. It is shown that turbu- lence is predominant in the microchannel of the crimped ribbon flame arresters under the defiagration and detonation conditions, and a new quenching criterion for the numerical simulation is proposed. The kinetics mechanism of Mansouri et al. among the four ones is the most accurate due to the best agreement of the pre- dicted outlet temperature at the experimental flameproof velocity with the autoignition temperature of propane-air. The species mass fraction profiles and the temperature distribution, which are too difficult to mea- sure due to the tiny dimension of the microchannel in experiments, are captured. The fundamental insights into chemical reactions and heat loss are well portrayed. It can be concluded that the integrated mathematical model established in this work can be used as a reliable tool for modeling, selecting and designing such type of crimped ribbon flame attesters with the propane-air medium in the future.展开更多
Based on viscoelastic theory, two new computational methods of solving linear equations and minimum value of the l-norm were put forward for transforming Kohlransch-William-Watts （KWW） function of viscoelastic mater...Based on viscoelastic theory, two new computational methods of solving linear equations and minimum value of the l-norm were put forward for transforming Kohlransch-William-Watts （KWW） function of viscoelastic materials to the generalized Maxwell model. The computational methods for the Maxwell model fitting were achieved in MATLAB software. It is found that fitting precision of the two methods is very high. The method of solving linear equations needs more fitting points and more numbers of Maxwell units. It makes the program of finite element analysis complex. While the method of solving minimum value of 1-norm can obtain very high precision only using less fitting points. These methods can fit not only experimental curve of KWW function, but also the experimental data directly.展开更多
The research on ditching is indispensable for civil airplanes made in China to obtain the airworthiness certificates.The suction force effect in the ditching process is a hot and difficult research topic.In this paper...The research on ditching is indispensable for civil airplanes made in China to obtain the airworthiness certificates.The suction force effect in the ditching process is a hot and difficult research topic.In this paper,the explicit method is employed to solve the discrete Lagrangian finite element equations.The Eulerian finite volume method(FVM) is used to solve the Eulerian control equations;the fluid-solid coupling is realized through the general coupling method.The model of large civil airplane ditching is simulated by Dytran and the model test in tank is carried out in the same condition.Based on the analysis on the impacts and generation of the suction force and a numerical example,we obtain the accurate ditching pressure and pitch angle,as well as the results from the simulation and test.The estimated pressure and pitch angles are consistent with the results in the test.In the simulation,where the suction force is considered,the attitude-time history curve is very similar to the one of the tests,whereas the attitudes in the calculation without suction force is far different from the test.It can be concluded from the results that the suction force is the key impact in ditching calculation and can be simulated by general coupling method.In addition,different weight characteristics and different initial pitch angles both result in different pressures of ditching.展开更多
Following the idea of Speziale＇s Very Large Eddy Simulation （VLES） method, a new unified hybrid simulation approach was proposed which can change seamlessly from RANS （Reynolds-Averaged Navier-Stokes） to LES （La...Following the idea of Speziale＇s Very Large Eddy Simulation （VLES） method, a new unified hybrid simulation approach was proposed which can change seamlessly from RANS （Reynolds-Averaged Navier-Stokes） to LES （Large Eddy Simulation） method depending on the numerical resolution. The model constants were calibrated in accordance with other hybrid methods. Besides being able to approach the two limits of RANS and LES, the new model also provides a proper VLES mode between the two limits, and thus can be used for a wide range of mesh resolutions. Also RANS simulation can be recovered near the wall which is similar to the Detached Eddy Simulation （DES） concept. This new methodology was implemented into Wilcox＇s κ- ω model and applications were conducted for fully developed turbulent channel flow at ReT = 395 and turbulent flow past a square cylinder at Re = 22000. Results were compared with LES predictions and other studies. The new method is found to be quite efficient in resolving large flow structures, and can predict satisfactory results on relative coarse mesh.展开更多
基金Supported by the National Key Research and Development Program of China(2016YFB0301701)the National Natural Science Foundation of China(21706268+4 种基金9143411421376254)the Postdoctoral Science Foundation of Qingdao Municipal Government(Y7330419DM)the Instrument Developing Project of the Chinese Academy of Sciences(YZ201641)State Key Laboratory of Safety and Control for Chemicals of China
文摘Crimped ribbon flame arresters are important safety devices in the chemical industry, especially for the danger- ous situations. Although proper design of arresters by the numerical simulation method is promising, its reliabil- ity and accuracy are dependent upon the mathematical model. In this work, an integrated mathematical model for the microchannel in the crimped ribbon flame attesters was set up; the fluid flow behavior and the sensitiv- ities of four chemical kinetics mechanisms of propane-air on the accuracy were analysed. It is shown that turbu- lence is predominant in the microchannel of the crimped ribbon flame arresters under the defiagration and detonation conditions, and a new quenching criterion for the numerical simulation is proposed. The kinetics mechanism of Mansouri et al. among the four ones is the most accurate due to the best agreement of the pre- dicted outlet temperature at the experimental flameproof velocity with the autoignition temperature of propane-air. The species mass fraction profiles and the temperature distribution, which are too difficult to mea- sure due to the tiny dimension of the microchannel in experiments, are captured. The fundamental insights into chemical reactions and heat loss are well portrayed. It can be concluded that the integrated mathematical model established in this work can be used as a reliable tool for modeling, selecting and designing such type of crimped ribbon flame attesters with the propane-air medium in the future.
基金Project (50605063) supported by the National Natural Science Foundation of ChinaProject(NCET-040753) supported by New Century Excellent Talents in University, ChinaProject (20050533037) supported by the Doctoral Program of Higher Education, China
文摘Based on viscoelastic theory, two new computational methods of solving linear equations and minimum value of the l-norm were put forward for transforming Kohlransch-William-Watts （KWW） function of viscoelastic materials to the generalized Maxwell model. The computational methods for the Maxwell model fitting were achieved in MATLAB software. It is found that fitting precision of the two methods is very high. The method of solving linear equations needs more fitting points and more numbers of Maxwell units. It makes the program of finite element analysis complex. While the method of solving minimum value of 1-norm can obtain very high precision only using less fitting points. These methods can fit not only experimental curve of KWW function, but also the experimental data directly.
基金supported by the National Natural Science Foundation of China (Grant No. 10772013)the National Technology Research and Development Program of China (Grant No. 2012AA112201)the Aeronautical Science Foundation of China (Grant No. 20100251007)
文摘The research on ditching is indispensable for civil airplanes made in China to obtain the airworthiness certificates.The suction force effect in the ditching process is a hot and difficult research topic.In this paper,the explicit method is employed to solve the discrete Lagrangian finite element equations.The Eulerian finite volume method(FVM) is used to solve the Eulerian control equations;the fluid-solid coupling is realized through the general coupling method.The model of large civil airplane ditching is simulated by Dytran and the model test in tank is carried out in the same condition.Based on the analysis on the impacts and generation of the suction force and a numerical example,we obtain the accurate ditching pressure and pitch angle,as well as the results from the simulation and test.The estimated pressure and pitch angles are consistent with the results in the test.In the simulation,where the suction force is considered,the attitude-time history curve is very similar to the one of the tests,whereas the attitudes in the calculation without suction force is far different from the test.It can be concluded from the results that the suction force is the key impact in ditching calculation and can be simulated by general coupling method.In addition,different weight characteristics and different initial pitch angles both result in different pressures of ditching.
基金supported by the National Natural Science Foundation of China (Grant No. 50936005)the National Basic Research Program of China (Grant No. 2010CB227302)
文摘Following the idea of Speziale＇s Very Large Eddy Simulation （VLES） method, a new unified hybrid simulation approach was proposed which can change seamlessly from RANS （Reynolds-Averaged Navier-Stokes） to LES （Large Eddy Simulation） method depending on the numerical resolution. The model constants were calibrated in accordance with other hybrid methods. Besides being able to approach the two limits of RANS and LES, the new model also provides a proper VLES mode between the two limits, and thus can be used for a wide range of mesh resolutions. Also RANS simulation can be recovered near the wall which is similar to the Detached Eddy Simulation （DES） concept. This new methodology was implemented into Wilcox＇s κ- ω model and applications were conducted for fully developed turbulent channel flow at ReT = 395 and turbulent flow past a square cylinder at Re = 22000. Results were compared with LES predictions and other studies. The new method is found to be quite efficient in resolving large flow structures, and can predict satisfactory results on relative coarse mesh.
