Papers by Keyword: Pulsating Flow

Abstract: Often due to the pressure gradient change in pressure systems the stationary flow pattern is disturbed initiating respective time-dependent change of hydraumechanical parameters at the cross-section. As a consequence of the pressure gradient change under the influence of varying friction and inertia forces unstable flow of fluid occurs. The study of this phenomenon presents important practical and theoretical interest.

Abstract: The oscillating flow is an important factor affecting the performance of the rotor–seal system. From the point of view of flow induced vibration, the nonlinear models of the rotor-seal system are presented for the analysis of the self-excited vibration, which is induced by interaction between the unstable seal fluid flow and the vibrating rotor. The nonlinear characteristics of flow induced vibration in the rotor-seal system are analyzed, and the nonlinear phenomena in the unbalanced rotor-seal system are investigated using the nonlinear model with the flow induced vibration.

Abstract: A pulsatile circulation system has been built to simulate aortic blood flow. The system has both upstream and downstream compliances and resistances to simulate the elasticity and resistances of blood circulation system. Influences of the compliances and resistances on the pulsatile pressure waveforms have been systematically studied using this system. We found that in absence of the compliances and the downstream resistance, it results in an oversize negative pulsation to the pressure waveforms. The downstream resistance hardly affects the structure of the pressure waveforms, whereas the mean amplitude of pressure increases along with the downstream resistance. The compliance can reduce the peak value of the pressure, which is unrelated to the location of the compliance but related to the elasticity in the system. With fixed upstream system elasticity, the pressure waveform is more stable.

Abstract: A study has been conducted on the heat transfer of various oscillatory frequencies of pulsation flow through a porous channel network subjected to a constant wall heat flux. The surface temperature distributions, pressure drop, unit thermal resistance and local Nusselt number for different oscillatory frequencies were mainly investigated.

Abstract: A mathematical model of pulsating laminar flow inside an annular space for power-law fluid was established basing on the background of petroleum engineering. The characteristic of pulsating flow was obtained by employed SIMPLE algorithm. The investigation result shows that the velocity profile and axial pressure gradient are affected by the frequency, amplitude, liquidity index and annular distance of reciprocating motion and the affection is violent near the inner wall.

Abstract: The heat transfer properties of pulsating flow around the tube with simple harmonic vibration were analyzed. The effect of the angle θ between the flow direction and the tube vibrating direction, which changes from 0° to 150°, on heat transfer properties was numerically investigated by the dynamic mesh technology of FLUENT. The results showed that the transient surface heat transfer coefficient decreases with increasing θ when amplitudes of pulsating flow or vibrating tube increase. Comparing with the still tube, the angle between the temperature gradient and the velocity vector is smaller when the tube vibrates along different directions, hence the field synergy performance is better, and the heat transfer performance is more enhanced.

Abstract: In order to study the influence of pulsating blood flow to robot and blood vessel, UDF programming of the inlet velocity is defined as the boundary condition, and the model simulate the turbulent blood flow. Moreover, in this situation, this paper analyzes the influence caused by blood parameters for the biggest surface pressure on robot. The results are showed that the variation of pressure and velocity is different on different position at 0.08s and 0.27s, and the surface pressure of the robot become greater by the increase of blood density or viscosity.

Abstract: Heat transfer enhancement by pulsating flow in a triangular grooved channel has been experimentally investigated. Effects of Reynolds number Re, Strouhal number St, pulsation amplitude A on the heat transfer enhancement were studied. The experimental results show that, the pulsating flow can significantly enhance heat transfer compared to the steady flow case, for instance, an enhancement of 115% is achieved at Re=400, A=0.5 and St=0.3. There exists an optimal Strouhal number corresponding to the maximum heat transfer enhancement factor. The heat transfer enhancement factor increases with the increase of Reynolds number and pulsation amplitude.

Abstract: Fluid flow and heat transfer characteristics of pulsating flow around the vibrating tube was numerically investigated by the dynamic meshing technique of FLUENT. The results showed the combined action of pulsating flow and vibration enhances the coefficient of heat transfer, and the surface heat transfer coefficient of vibrating tube increases with the increment of the tube vibration amplitude, frequency and pulsating flow amplitude, and pulsating flow frequency has less affected. The main reason that pulsating flow enhances heat transfer is the secondary flow, generated by the combined effect of pulsating flow and tube vibration, enhances momentum and energy transfer.

Abstract: The mechanism of heat transfer enhancement of pulsating flow in a spiral fluted tube was researched by CFD (computational fluid dynamics) software FLUENT. Numerical results showed that pulsating flow leads to cyclical fluctuation of outlet pressure and the extent of fluctuation increases with increasing the pulsating flow frequency. Moreover, the pulsating flowing causes whirlpools near the spiral flute and the vortices generate, drift, and fall off periodically. The optimum pulsating frequency in the spiral fluted tube is 6HZ and the optimum amplitude A is equal to 0.7 approximately when the Reynolds number is 1683.