# CFD method for High Re flow

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 May 28, 2001, 03:55 CFD method for High Re flow #1 Toshiyuki Arima Guest   Posts: n/a Dear all, I am solving a flowfield around object which moves at velocity of 50-100 m/s using a Characteristic Galerkin method (The Reynolds number is around 10^7). As you know, for this range of flow, it is difficult to solve it, even if the technique for which compressible flow or imcompressible one is used. Then all speed formulation with a preconditioning (e.g., E. Turkel, J. Comp. Phys, 1987) has been used to solve the imcompressible and low speed compressible equations. But, I think that it is a long way to implement this method into my imcompressible FEM flow solver. Furthermore, I think that it is not necessary for me to solve the flowfields in so wide range of flow velocity. (I do not treat a shock wave). Does anyone tell me good references (paper or text book) in which the method to relatively easily enhance the imcompressible code so that one can solve the flowfiels in the middle of the imcompressible and compressible regimes, in order to treat a weak compressible effects?

 May 28, 2001, 13:08 Re: CFD method for High Re flow #2 John C. Chien Guest   Posts: n/a (1). Your problem seems to be related to the method you are using. (2). My suggestion would be: (a). define your problem first. (b). define the Reynolds number of your problem, (c). define the Mach number of your problem, (d). define the characteristics of your flow problem, steady, unsteady, laminar or turbulent, (e). once you have these information, then do the journal search to find out what has been done in the past. (it is hard to invent something, especially in cfd) (f). study the previous methods used and pick a couple of methods for your problem. (3). If you are dealing with high Reynolds number flow, then you will have to deal with turbulence modeling as well. (4). Anyway, the starting point is always : your flow problem. What flow problem are you trying to solve?

 May 29, 2001, 10:58 Re: CFD method for High Re flow #3 Toshiyuki Arima Guest   Posts: n/a Thanks, Mr. Chien. I had to make question comprehensible more in detail. I would like to solve the flowfield around a couple of wings with large attack angle. The Reynolds number is about 10^7, as already mentioned. The inflow Mach number is less than 3.0 ( 0.5 - 3.0). The flow may be unsteady, basically, and turbulent. However, I am interested in the phase (and time) average quantities for the harmoniously oscilating solution. The some turbulence models (high-Re k-e model with a wall function and some low-Re K-e models) was implemented to solve the flowfield in my code. Anyway, my question is that how can I approach to get a numerical solution of this kind of flowfield, efficiently. If we approach it with an imcompressible scheme, we will not be able to get reasonable solution due to inadequacy of the governing equations. If we approach it with, compressible scheme, then we will be annoyed by a numerical instability due to the so-called compressible limit (for low Mach number). I know that one possible choice I can use to this kind of problem would be to use the all-speed algorithm with a preconditioning method. But, now, I am searching another method that I can solve this type of flow easier, since I do not deal with a wide range for the flow Mach number (i.e., I do not deal with a shock wave), but a weak compressibility. Will anyone give me some advices or references?

 May 29, 2001, 11:18 Re: CFD method for High Re flow #4 Toshiyuki Arima Guest   Posts: n/a Sorry ! One digit was mistook . The inflow Mach number is less than 0.3 ( 0.1 - 0.3).

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