We present some hydrodynamical results for a thermal model of solar flares with a high initial coronal density (5-11 × 1010 cm-3) in the flaring loop. The thermal energy is assumed to be released around the top of the loop. The results of the hydrodynamic simulation show that, in the initial phase of the flare, there is always a strong downward motion in the corona. This motion with a velocity as large as 700 km s--1 can last a few tens of seconds, leading to a pronounced redshift of the Ca XIX W line. This is not consistent with the observations of majority of flares, which show predominantly blueshifted or blue-asymmetric Ca XIX and Fe XXV lines. However, the results could account for the redshifted Ca XIX emission observed in a small number of flares, indicating a high initial coronal density in these flares. We conclude that only when the initial coronal density is smaller than 1010 cm-3 can the strong downward motion of the coronal material at the early phase of the flare be suppressed. When we combine the present and previous results of flare simulations, it appears that a model with both thermal and nonthermal energy sources may be more realistic in describing the flare hydrodynamics.