Under oceanic conditions

the coolant in the loop of a floating nuclear reactor(FNR) experiences periodic fluctuations

which affects the system's thermal and hydraulic characteristics. A combination of theoretical derivation and numerical simulation is employed to investigate the velocity and temperature distribution characteristics within a pipe under pulsating flow conditions. Moreover

the influence of different numerical simulation boundary conditions on the velocity and temperature distribution in a circular tube under pulsating flow is compared. The results show that

under high-frequency pulsating flow conditions

laminar flow inside the pipe will experience backflow near the wall

and the wall effect will increase with the pulsation frequency. Using pulsating velocity inlet and pressure outlet as numerical simulation boundary conditions fails to predict this backflow phenomenon. However

employing fluctuating pressure inlet and flow outlet effectively captures the backflow occurrence in high-frequency pulsating flow. Concurrently

the temperature within the pipe fluctuates under pulsating flow conditions

and the amplitude of temperature fluctuations gradually decreases when the pulsation frequency increases. Numerical simulation can well simulate the temperature distribution in the pipe under pulsating flow conditions

with an error of less than 2%.The research results can provide reference for non-stationary numerical simulation methods.