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This study presents the hydrodynamic simulation for high energy large-size Nd:YAG liquid-cooled laser amplifier. Based on hydrodynamic equations, the heat transfer coefficient as a function of cooling fluid velocity is derived. The velocity of cooling fluid could be chosen as 0.8m/s by considering critical Reynolds numbers for laminar and turbulent flows. In order to assess the uniformity of the cooling fluid, a four-channel fluid model is established. The uniformity of four D2O fluid channel in gain region are 98.5%, 98.7%, 98.5%, 98.6%, respectively. Besides, A simple Nd:YAG heat transfer model is built for assessing the cooling capacity of fluid, which is based on the calculation of heat transfer coefficients equation. The temperature differences of central and marginal gain medium planes is 3.451K and 1.951K, respectively, which is close to 3.255K and 1.778K calculated in the heat-fluid-solid coupling model. Based on the heat fluid-solid coupling model, the total wavefront aberration is 0.266λ cooled by D2O. Finally, another cooling fluid FC770 has been compared with D2O. In terms of fluid uniformity, the uniformity of four FC770 fluid channels in the gain region are 98.5%, 98.7%, 98.5%, 98.6%, respectively, which is close to D2O. In terms of heat effect, the heat transfer coefficients of D2O is larger than FC770. And total wavefront aberration of Nd:YAG cooled by FC770 is 0.840λ, which is larger than D2O. Eventually, the thermally induced wavefront aberrations of D2O and FC770 are 0.0475λ and 0.6092λ, respectively. The calculated results showed that D2O is a better cooling fluid than FC770.
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