# Lax-Friedrichs flux

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 July 30, 2011, 10:02 Lax-Friedrichs flux #1 New Member   aaaaaaaaaaaaaa Join Date: Apr 2011 Posts: 23 Rep Power: 7 Have anyone a paper which explain how lax-friedrich(approximate riemann solver) is derived? Also if we suppose that (u+) is the values of a volume , (u-) the values of neighbour volumes and F the flux then the lax-friedrichs flux gives: F=0.5*( (F+) + (F-) ) - a*( (u-) - (u+) ) This is applied by all faces of a initial volume regardless of its outward unit vector?

 July 30, 2011, 12:45 #2 Senior Member   cfdnewbie Join Date: Mar 2010 Posts: 557 Rep Power: 12 There's nothing too fancy about the LF-flux....its the average, penalized by the jump to add a strong dissipative constant.... not sure about the original paper, anybody has a hint??? you compute your F by the formula given above, and then do int (F*n) dx to take the normal into account... hope this helps a bit!

 July 30, 2011, 17:09 #3 New Member   aaaaaaaaaaaaaa Join Date: Apr 2011 Posts: 23 Rep Power: 7 Yes , sure. The third term is the dissipative term. Simply , i did not know if it has a complex theory under of it (due to appearance of eigenvectors as dissipative multiplier). With other words, i want to learn what assumptions do for to solve approximate the Riemann problem and finally result at this simply relation. For other cases as HLLC or HLL there is a assumption on a number of waves. Here?

July 31, 2011, 03:52
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Quote:
 Originally Posted by panou For other cases as HLLC or HLL there is a assumption on a number of waves. Here?
Hm, I'm only familiar with the LOCAL LF (also called Rusanov), where the a in your equation above is the local largest EV.... so that's your fastest wave...

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