In a viscous flow, viscous dissipation -- transforming kinetic energy to heat -- have two sources, namely average flow kinetic energy and turbulent (flow) kinetic energy. Usually the turbulent kinetic energy will dominate.
1) When fluid flow is 'transformed' from high to low Reynolds number, is all turbulent flow kinetic energy transformed to heat?
2) What is the rate of turbulent flow viscous dissipation in a Francis turbine draft tube (say, from runner to outlet)?
Hi, for (1)
When you write out the governing equations of the kinetic energy, you will see that the kinetic energy of the mean flow can exchange with the kinetic energy of the fluctuating flow. Typically you are right that "turbulent flow kinetic energy transformed to heat", But depends on the specific condition, the turbulent flow kinetic energy can be probably converted to the energy of the mean flow as well.
I have no idea about the Francis turbine. Sorry no answer.
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