Vortex stretching involves an exchange of energy because the strain rate performs deformation work on the vortices that are stretched. The amount of energy gained by a disturbance with velocity components in a strain rate field s_ij is

unit mass

For the case of Fig. 23.1, the energy exchange rate is

(23.4)

According to Eqn. (23.3), ω₁ is increased. By definition

(23.5)

The implication of the above is a definite increase in . may also increase, but slowly. is decreased and thus by definition

(23.6)

decreases. At large time, these together produce an increase in T.