University of Wisconsin-Madison

Video shows ANSYS Fluent simulation of the turbulence, pressure and wall heat flux on a swimming leatherback sea turtle.

Problem:

Researchers at the University of Wisconsin-Madison (UWM) wanted to predict where leatherback sea turtles could exist under climate change. To make this prediction, UWM needed to better understand the heat budget (heat production and heat transfer) of a swimming leatherback sea turtle.

It is difficult to analyze an aquatic animal's heat budget because of strong links among heat transfer, metabolic rate and aquatic motion, as well as the difficulty in measuring each of these. Complex interactions between thrust and drag on a deforming body makes it difficult to quantify a moving animal's useful work and to determine how rapidly a self-propelling, aquatic organism loses metabolic waste heat. With an ANSYS Fluent user-defined function, UWM examined the turtle’s flipper stroke to measure the power and heat flux of a swimming leatherback.

Solution:

UWM researchers drew an anatomically realistic leatherback in NURBS format, imported it into ANSYS DesignModeler and enclosed one side of the model in a half cylinder. An entire fluid domain with tetrahedral elements was meshed using ANSYS Meshing. The researchers wrote a Fluent UDF that described the turtle’s swimming motion, which they described mathematically by analyzing videos of leatherbacks swimming freely. The flipper motion was smooth and divided into four zones. The 14 percent of the flipper closest to the shoulder was the transition zone from no motion to steady roll and yaw. The next 22 percent of the flipper was the transition zone from steady roll and yaw to steady roll, yaw and pitch. The next 21 percent of the flipper was a zone of constant roll, yaw and pitch. The last 43 percent of the flipper was the transition zone from steady roll, yaw and pitch to roll, yaw, pitch and bend. The flipper stroke also had four phases. There was a down stroke, a turn at the bottom of the stroke, an up stroke and a turn at the top of the stroke. The simulation used the k-ω SST model with a constant velocity inlet and zero pressure outlet at the front and back of the turtle's half cylinder enclosure.

Software used:

  • ANSYS CFD-Post
  • ANSYS DesignModeler
  • ANSYS Fluent
  • ANSYS Meshing