Which of the following statements on laminar and turbulent airfoils is incorrect?

Question

Turbulent airfoils have the transition location closer to the leading edge than laminar airfoils

The NACA 6-series airfoils are laminar airfoils

Laminar flow can be achieved by irregularities in the surface, like zig/zag strips.

The difference in drag between a laminar and a turbulent airfoil can be as large as 10%

Answer 1

Let's evaluate each of the statements one by one:

1. Turbulent airfoils have the transition location closer to the leading edge than laminar airfoils: This statement is generally correct. In turbulent airfoils, the transition from laminar to turbulent flow often occurs sooner along the airfoil compared to laminar airfoils, which maintain laminar flow further back.

2. The NACA 6-series airfoils are laminar airfoils: This statement is correct. The NACA 6-series airfoils are specifically designed to promote laminar flow over a significant portion of the airfoil, hence they are considered laminar airfoils.

3. Laminar flow can be achieved by irregularities in the surface, like zig/zag strips: This statement is incorrect. Irregularities such as zig/zag strips typically disturb the flow and can lead to boundary layer transition to turbulence. These features are generally not conducive to maintaining laminar flow, as they promote mixing and turbulence.

4. The difference in drag between a laminar and a turbulent airfoil can be as large as 10%: This statement is also generally considered correct, as laminar flow can have lower drag due to less friction compared to turbulent flow.

Given this analysis, the incorrect statement is:

Laminar flow can be achieved by irregularities in the surface, like zig/zag strips.