Direct numerical simulations of spots

Although many properties of turbulent spots have been determined by laborat ory measurements and flow visualization, there still remain unanswered ques tions about the mechanisms involved in the spreading of spots, the role of instability waves, and the structure of the turbulent flow within and the n on-turbulent but modified flow outside spots, Direct numerical simulations offer detailed, well-resolved data which could reveal these mechanisms. A f ew such simulations have been done in flat plate boundary layers, in channe l flows (Poisueille and Couette flows) and in pipe flows. Although one stud y has examined the growth and breakdown of instability waves at the edges a nd another has computed particle trajectories to determine where fluid is e ntrained, most of these studies have only reached the stage of establishing the correctness of the simulations by comparisons with features observed i n laboratory flows. However, it is a reasonable expectation that in the nea r future, simulation studies will begin to make definitive statements about mechanisms of spot growth and propagation.