abnormal reaction rate coefficients?

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 May 29, 2001, 04:59 abnormal reaction rate coefficients? #1 peter.zhao Guest   Posts: n/a When I calculate a thermochemical nonequilibrium flow past a blunt cone at high Mach number by N-S equations,I find the reaction rate coefficients is so large that they exceed the range of single precision real,which in turn results in the blow-up of my program.Although I scan my program again by again,I find no problems on my formulae,which are all taken from C.Park's "nonequilibrium hypersonic aerodynamics". Peter A.Gnoffo shows a limit should be imposed on the temperature used to compute the reaction rate coefficients on NASA TM 4674,but I don't know how to implement his method. All recommendations are welcomed! Thanks in advance.

 May 30, 2001, 04:37 Re: abnormal reaction rate coefficients? #3 peter.zhao Guest   Posts: n/a Thank Dotsikas for your recomendations. I want to further explain my situation.I use two-temperature model in computation.As you said,I solve the translational temperature by explicit formula and the vibrational temperature by Newton iteration.The heat capacity is the function of temperature.The blunt cone is the experimental model of RAMC-3 at 76.3 Km altitude with the velocity 7.65km/s.The reactions, their rate coefficient and the equilibrium constant are those of Park's model from "nonequilibrium hypersonic aerothermodynamics".The initial flow field are free stream.I use LU-SGS and MUSCL TVD scheme. From the beginning of computation,I found the very high abnormal reaction rate coefficient even the translational temperaure is not very high.After several iterations,The program blow up on account of float overflow even at very low CFL number. However,I succeeded in yielding a good result by Dunn-Kang's model.I don't know the reasons.

 June 6, 2001, 03:06 Re: abnormal reaction rate coefficients? #5 peter.zhao Guest   Posts: n/a Jannis Dotsikas: I'm very apperciative to your comments. I'v found the reason.It's necessary to limit the control temperature,which is used to calculate the reaction rate coefficients,in order to ensure the running of program.As for nonequilibrium hypersonic flow at high altitude,the temperature is so low as not to ignite the dissociation reactions.However,the reaction rate coefficients and the equilibrium coefficients are yielded at the temeprature far beyond the temperature of free stream,so it will lead to float overflow to calculate the reaction rate coefficients at such low temeprature.After I impose a lower limit temperature 1000K as Gnoffo used,I obtain a satisfactory result. Thanks a lot for your precious suggestions again.

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