DLR natural and hybrid transonic laminar wing design incorporating new methodologies

Abstract

In the present work natural laminar flow (NLF) and hybrid laminar flow (HLF) wing designs are presented which were obtained by combining new methodologies with experience and knowledge obtained with traditional laminar wing design methods. The NLF wing design is performed for wing-body configurations with backward swept wing (BSW) and forward swept wing (FSW). Initial aerofoil sections were obtained by using a new sectional conical wing method which allows the design of transonic wing sections, taking into account the effects of sweep and taper for the computational cost of a 2D method. Except for flow regions with strong 3D influence, wings constructed with these aerofoils showed an acceptably large region with laminar boundary layer and small shocks at design and specified off-design conditions. For regions close to the body and the tip a 3D inverse design method was further required. For the BSW case, due to cross flow a premature transition occurred. Therefore, a HLF panel was required to obtain a larger laminar region. A suction distribution was obtained using the suction distribution module of the automated target pressure generator (ATPG). This generator optimises the pressure distributions in terms of minimising drag while keeping certain boundary conditions constant, e.g. lift and momentum. Using the ATPG, the laminar extent of the BSW NLF design could be further improved for the inboard wing. With the new methodologies design work was reduced. They lead to a design with reserves that allow for acceptable off-design performance qualities by keeping the wing laminar over a wide range of flight conditions.

Feasibility of skin-friction field measurements in a transonic wind tunnel using a global luminescent oil film

“…To obtain reference skin-friction values in the laminarflow region, compressible boundary-layer calculations were carried out using the laminar boundary-layer solver COCO (Schrauf 1998), which is a well established code for boundary-layer stability analysis and laminar wing design (see Streit et al (2015) and Schrauf and von Geyr (2020), among others). The surface pressure distributions, measured by means of the pressure taps, served as inputs for the boundary-layer computations, together with the freestream Mach number, the chord Reynolds number, and the freestream static temperature.…”

DLR transonic inverse design code, extensions and modifications to increase versatility and robustness

“…The second introduced modification is smoothing of the geometry. The solution algorithm of the governing equation (Equation (1)) does not distinguish between an elliptic (subsonic) or a hyperbolic (supersonic) character of Equation (1). The character of the governing equation (Equation (1)) is elliptic or hyperbolic if:…”

“…Examples of recent wing designs are given in Ref. 1. But new applications and configurations have shown limitations as well as extension possibilities of the inverse design code.…”

“…distribution is found which minimizes the drag, i.e. it compromises laminar flow extent against wave drag (1,19) . According to the requirements, constraints and objectives of a given aerodynamic design task the most appropriate design tool has to be selected.…”

“…Especially for applications concerning the design of transonic aerofoils/wings with Natural Laminar Flow (NLF) and Hybrid Laminar Flow (HLFC), the inverse design code was the preferred wing design tool within DLR. Examples of recent wing designs are given in Ref. 1.…”