For my master thesis I'm simulating the cooling of an 2.5D microchip (2 dies next to each other on an interposer (slice of silicium with interconnections)). So I want to calculate the flow over the chip and the attached ducted straight fin heat sink. The fluid can only flow through the fins of the heat sink. The inlet velocity is over 2 m/s so that there is no influence of natural convection. The flow can be seen as a combination of a forward facing step and a backward facing step.
I calculated the Reynolds number between the fins and it was 1075. So the flow should be laminar (or at least that is what i think). Because of the high velocity the flow because unsteady behind the heat sink (I can only calculate the flow with the transient option in fluent). I assumed that it was an unsteady laminar flow. But when I look to the velocity in a point, it isn't periodic in time. So the flow behind the heatsink could be in the transitional or turbulent regime. But I'm not sure of that.
Is there a way to check the regime behind the heatsink?