# About compressible flow at low mach

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 October 26, 2009, 08:31 About compressible flow at low mach #1 New Member   WANG Join Date: Oct 2009 Posts: 1 Rep Power: 0 Dear CFD friends, now,I have a question about calculation of compressible flow at low mach,But I can not get a good result.I can not find reasons. Calculation condition as follows: [1]stream flow Mach number M=0.01 [2]Rey=6e4 [3]space: MUSCL method Roe average method [4]time: LUSGS method [5]Laminar flow method(Compressible flow Code is used) By these conditions,for example,If Roe-average method is used at very low Mach number(Mach number M=0.01) by Compressible flow Code,Can I get good result? Thanks

 October 26, 2009, 10:19 #2 Super Moderator   Praveen. C Join Date: Mar 2009 Location: Bangalore Posts: 342 Blog Entries: 6 Rep Power: 18 You will get very bad results at such low mach numbers with a compressible code. You need to use some preconditioner. A easy preconditioner for roe scheme can be found in Herve and Viozat http://citeseerx.ist.psu.edu/viewdoc...10.1.1.35.2610

 October 26, 2009, 21:21 #3 New Member   Rudhi Kurniawan Join Date: Oct 2009 Posts: 1 Rep Power: 0 Hi, im mechanical engineering student and i make an unsteady compressible navier-stokes simulation at low speed, using C++, mccormack scheme. when i place an obstacle, i got good result, with 1500 iteration i can see that the flow is convergence and it has vortex flow on it. Beautiful ... The problem is interaction between fluid flow and boundary is very weak, what should i do to fix it??? It is channel flow with u = 3 m/s, channel length 10 cm, height 10 cm. can somebody help me???