  This paper relates to the parametric study of tunnel hoods in order to reduce
the shape, i.e the temporal gradient, of the pressure wave generated by the
entry of a High speed train in tunnel. This is achieved by using an in-house
three-dimensional numerical solver which solves the Eulerian equations on a
Cartesian and unstructured mesh. The efficiency of the numerical methodology is
demonstrated through comparisons with both experimental data and empirical
formula. For the tunnel hood design, three parameters, that can influence the
wave shape, are considered: the shape, the section and the length of the hood.
The numerical results show, (i) that a constant section hood is the most
efficient shape when compared to progressive (elliptic or conical) section
hoods, (ii) an optimal ratio between hood's section and tunnel section where
the temporal gradient of the pressure wave can be reduced by half, (iii) a
significant efficiency of the hood's length in the range of 2 to 8 times the
length of the train nose. Finally the influence of the train's speed is
investigated and results point out that the optimum section is slightly
modified by the train's speed.
