دانلود رایگان مقاله تاثیر شنا کردن ماهی در الگوی جریان مخازن دایره

abstract

The effect of swimming fish on the average velocity and velocity profile of a circular tank was studied. Working with different inlet diameters and flow rates, nine different impulse forces (configurations) were evaluated. Each configuration was tested with and without fish, and the effects of two different fish sizes were compared. The velocity profiles in experiments with fish presented a considerable reduction in velocity in the centre ofthe tank near the outlet, which was a consequence ofthe increase in the kinematic eddy viscosity due to the turbulence introduced by fish swimming. A flattening of the angular velocity profile was observed in the central area of the tank, which had a radius of about 0.3 m (18% of the total volume of the tank). A previous model proposed by Oca and Masaló (2013) was modified in order to better describe the distribution of velocities in the central volume of a tank with swimming fish. The proposed modifi- cation was based on Burgers’ proposal for a bathtub vortex, which implies the determination of the parameter (1 − e−˛r2 ), where r is the radius and the values were experimentally obtained for each tank configuration, in which they increased with the impulse force. The average velocities in the tank were proportional to the square root of the impulse force in experiments with and without fish. Experiments with fish presented lower average velocities, which imply higher tank resistance coefficients. At similar stocking densities (14.6 kg/m3), the increase in the tank resistance coefficients obtained with small fish sizes (154 g) were slightly higher than those obtained with bigger fish sizes (330 g).

4. Conclusions

This work analyses the differences observed in average velocities and the velocity profile in a circular tank (1.44 m diameter) without fish and with fish of different sizes at a density of 14 kg/m3. Average velocities obtained in tanks with swimming fish were lower than those obtained with identical impulse force and flow rate in a tank without fish. The decrease in average velocity implied a higher tank resistance coefficient (Ct), indicating an increase in water resistance to flow with fish. Also it was observed that average velocities in a circular tank with fish were proportional to the square root of the impulse force, as had been demonstrated by Oca and Masaló (2013) in a tank without fish. Differences in average velocities are a consequence of the differences observed in the velocity profile in experiments with and without fish. It was demonstrated that the main differences in the velocity profile occurred in the area near the tank outlet, where velocities were much lower in experiments with fish. Velocities near the tank walls were also lower in tanks with fish, but differences were scarce. Experiments with big (approx. 330 g) and small (approx. 154 g) fish did not present greater differences in velocity profiles. The lower velocities in the central area of the tank with fish can be conferred to the turbulence introduced by swimming fish, which increase the kinematic eddy viscosity and thus generate a flattening I. Masaló, J. Oca / Aquacultural Engineering 74 (2016) 84–95 95 of the angular velocity profile in the central area of the tank. This is noticeable in a radius of about 0.3 m (18% of the total volume of the tank). This work proposes some improvements to include in the current available model (Oca and Masaló, 2013) in order to have a faithful prediction of flow patterns in circular fish rearing tanks, especially when modeling the velocities near the central area of the tank. The proposal combines the Oca and Masaló model with Burgers’ proposalfor a bathtub vortex. The velocity profile obtained with the Oca and Masaló model was multiplied by(1 − e−˛r2 ), and the parameter in Burgers’ proposal is experimentally determined in experiments with and without fish, with its value being nearly proportional to the impulse force of each tank configuration. It must be observed that the lower the value, the higher the effect on velocities in the central area of the tank. The value obtained in experiments without fish was about forty times higher than in experiments with fish.