COMPARISON BETWEEN THE BOLTZMANN AND BGK EQUATIONS FOR UNIFORM SHEAR-FLOW

The exact fourth-degree moments derived in the preceding paper from th e Boltzmann equation for Maxwell molecules under uniform shear flow ar e compared with those obtained from the BGK and the Gaussian approxima tions. It is shown that the BGK results are closer to the exact ones t han the Gaussian results. However, the deviations become significant a s the shear rate increases.