What determines boundary layer transition location?

What determines boundary layer transition location?

• A. It is where flow shifts from laminar to turbulent; surface roughness and pressure gradients can trigger earlier transition
• B. It is where the flow becomes supersonic
• C. It is fixed and unaffected by surface finish
• D. It only occurs at high Reynolds numbers

Answer: (A)

The transition location is the point along the surface where the boundary layer changes from laminar to turbulent. This shift happens when disturbances in the wall region grow enough to make the flow inside the boundary layer unstable. Surface roughness introduces those disturbances, triping the flow into turbulence sooner. Pressure gradients along the surface also affect stability: adverse gradients tend to destabilize the boundary layer and promote earlier transition, while favorable gradients help keep the flow laminar longer. Because of these factors, the transition point is not fixed and can move with changes in surface finish, surface conditions, and external disturbances. The other ideas misstate the concept: boundary layer transition is not defined by reaching supersonic speeds, it is not immune to surface finish, and it does not require high Reynolds numbers alone to occur.

The transition location is the point along the surface where the boundary layer changes from laminar to turbulent. This shift happens when disturbances in the wall region grow enough to make the flow inside the boundary layer unstable. Surface roughness introduces those disturbances, triping the flow into turbulence sooner. Pressure gradients along the surface also affect stability: adverse gradients tend to destabilize the boundary layer and promote earlier transition, while favorable gradients help keep the flow laminar longer. Because of these factors, the transition point is not fixed and can move with changes in surface finish, surface conditions, and external disturbances. The other ideas misstate the concept: boundary layer transition is not defined by reaching supersonic speeds, it is not immune to surface finish, and it does not require high Reynolds numbers alone to occur.