Effect of screens on the turbulent flow in the quiescent zone of a rectangular aquaculture raceway

• Published in: Aquacultural engineering 2013-11, Vol.57, p.48-53
• Main Authors: Fizer, Eric, Gray, Donald D., Semmens, Kenneth J.
• Format: Article
• Language: English
• Subjects: Acoustic Doppler velocimeter; acoustics; Agnatha. Pisces; Animal and plant ecology; Animal aquaculture; Animal productions; Animal, plant and microbial ecology; Aquaculture; Biological and medical sciences; Debris; Dogwood Lake; Fish; fish culture; Fluid dynamics; Fluid flow; Fresh water ecosystems; Fundamental and applied biological sciences. Psychology; General aspects; Quiescent zone; Raceway; raceways; rearing; Screens; Synecology; Turbulence; Turbulence intensity; Turbulence measurements; Turbulent flow; Vertebrates: general zoology, morphology, phylogeny, systematics, cytogenetics, geographical distribution
• ISSN: 0144-8609; 1873-5614
• DOI: 10.1016/j.aquaeng.2013.07.001

•ADV measured mean velocity and turbulence characteristics in quiescent zone of raceways.•Data at 10Hz for 360s used to find mean and root-mean-square velocities, and turbulence intensity.•When clean, smaller screens promote more uniform mean velocity profiles and reduce turbulence.•Small, clean screens enhance settling of solids.•Dirty screens reshape mean profile and increase turbulence. An acoustic Doppler velocimeter (ADV) was used to measure detailed vertical profiles of mean velocity and (for the first time) turbulence characteristics at the center of the quiescent zone (QZ) of operating aquaculture raceways. Instantaneous velocities were recorded at 10Hz and averaged over a 360-s time interval in order to derive mean velocities, root-mean-square velocities, and turbulence intensities. The type and cleanliness of the screen separating the QZ from the fish rearing zone was found to be significant. When screens are free of growth and debris, smaller screens promote more uniform mean streamwise velocity profiles, reduce the streamwise root-mean-square (rms) velocities near the floor, and greatly reduce the turbulence intensities in the lower half of the profile. These effects suggest that smaller screens may be used to enhance the setting efficiency of QZs, but this conclusion may not be valid when the screen accumulates significant amounts of debris and algal growth. This condition dramatically alters both the magnitude and the shape of the mean and turbulence profiles. The slower mean velocity produced by a dirty screen should tend to enhance settling, but the higher turbulence has the opposite effect. It is not clear which effect is dominant. The resolution of these questions will require more comprehensive measurements of velocity and solids concentration.