SOME INTERFERENCE EFFECTS IN FLOWS THROUGH ROWS OF SURFACE PROTRUSIONS
Forced convection heat transfer can be improved by staggered arrays of surface protrusions acting as effectively as the optimum rib type roughness (1). The present work shows that for typical pitches interference effects may cause odd and even numbered rows to act differently. This is shown for a particular type of protrusion, but ongoing tests indicate that it will occur with other shapes of protrusion also.
Protrusions in the first row produce horse-shoe shaped vortices which approach one another as the flow moves to the second row. The trailing legs of upstream vortices approach a protrusion in the second row and suppress the vortex generation there. The flow then proceeds to the third row where vortices are again generated.
The process is then repeated, the vortex generation at the fourth row being effectively suppressed.
The result is that the odd numbered rows in the array generated larger wakes than the even numbered rows, and have higher drag coefficients and produce a bigger improvement in heat transfer than do the even numbered rows.
This seems to be a stable situation, with the performance of any row depending upon whether it is odd or even numbered.