Design of a slotted, natural-laminar-flow airfoil for transition validation experiments

Airfoils tested at low speeds generally produce surface pressure distributions that differ substantially from those measured at transonic conditions, which in turn results very different boundary-layer characteristics even for the same Reynolds number. A methodology is presented for mapping transonic pressure gradients to an equivalent low-speed airfoil. It is applied to the design of a low-speed, slotted, natural-laminar-flow (SNLF) airfoil is designed that emulates the pressure distributions of an SNLF airfoil designed for a transonic commercial transport. The overall process mirrors the development of the transonic airfoil by beginning with a single-element airfoil and then modifying it to include an aft element. An inverse design method based on conformal mapping was developed and employed to determine the necessary geometry of the low-speed single-element airfoil. Analysis of the new SNLF airfoil confirms that the design objectives were met.