Resurrection of "second Order" Models of Traac Ow?

We introduce a new second orderr 1 model of traac ow. As noted in 2], the previous "second order" models i.e models with two equations (mass and momentumm) lead to nonphysical eeects, probably because they try to mimic the gas dynamics equations, with an unrealistic dependence of the acceleration with respect to the space derivative of the pressuree. We simply replace this space derivative by a convective derivative, and we show that this very simple repair completely resolves the inconsistencies of these models. Moreover, our model nicely predicts instabilities nearby the vacuum i.e. for a very light traac.