Hydrodynamical effect of parallelly swimming fish using computational fluid dynamics method.

Area of Science:

• Fluid Dynamics
• Biomechanical Engineering
• Ichthyology

Background:

• Fish schooling behavior is common, but the precise hydrodynamic mechanisms enhancing energy efficiency remain poorly understood.
• Existing fish swimming models often use simplified movements and lack detailed simulation of actual swimming patterns.

Purpose of the Study:

• To analyze Biwa salmon swimming behavior using image analysis to create a realistic swimming motion model.
• To investigate the hydrodynamic forces and energy efficiency of fish swimming in parallel formation using computational fluid dynamics (CFD).

Main Methods:

• Image analysis of Biwa salmon (Oncorhynchus sp.) to formulate realistic swimming motions.
• Computational fluid dynamics (CFD) simulations using the formulated swimming motion to analyze fluid forces.
• Comparison of swimming efficiency and flow fields at various inter-fish distances (0.4L, 0.8L, 1.2L).

Main Results:

• Parallel swimming of two fish models showed a 10% increase in efficiency at a separation of 0.4L.
• Flow fields revealed reduced apparent flow speeds (0.5-2.0L) and elevated pressure at the caudal fin.
• Isopleth maps indicated a thin aft body is crucial to avoid negative thrust.

Conclusions:

• Hydrodynamic interactions significantly improve fish swimming efficiency, particularly at optimal inter-fish distances.
• Realistic fish swimming motion modeling is essential for accurate CFD analysis of schooling benefits.
• Body shape optimization, especially the aft section, plays a key role in efficient propulsion.