A multi-fidelity system of computer codes for the analysis and design of vehicles having extensive areas of laminar flow is under development at the NASA Langley Research Center. The overall approach consists of the loose coupling of a flow solver, a transition prediction method and a design module using shell scripts, along with interface modules to prepare the input for each method. This approach allows the user to select the flow solver and transition prediction module, as well as run mode for each code, based on the fidelity most compatible with the problem and available resources. The design module can be any method that designs to a specified target pressure distribution. In addition to the interface modules, two new components have been developed: 1) an efficient, empirical transition prediction module (MATTC) that provides n-factor growth distributions without requiring boundary layer information; and 2) an automated target pressure generation code (ATPG) that develops a target pressure distribution that meets a variety of flow and geometry constraints. The ATPG code also includes empirical estimates of several drag components to allow the optimization of the target pressure distribution. The current system has been developed for the design of subsonic and transonic airfoils and wings, but may be extendable to other speed ranges and components. Several analysis and design examples are included to demonstrate the current capabilities of the system.
Within the European Project Telfona the Pathfinder Model was designed, analyzed numerically, constructed and tested with the aim of obtaining a laminar flow testing capability in the European Transonic Wind Tunnel (ETW). The model was designed for natural laminar flow (NLF) for transonic flow conditions with high Reynolds number.Results of pre-test numerical analysis demonstrated that the Pathfinder wing pressure distribution was adequate for providing calibration test points. The ETW tests provided pressure distribution data while transition positions were determined from images using the Cryogenic Temperature Sensitive Paint Method (cryoTSP). The evaluation of this data with several transition prediction tools was used to establish the transition N-factor values for ETW. In this work, after-test CFD solutions are obtained using numerical Navier-Stokes solutions. In the first part of this work, numerical results are given which verify the requirements of the Pathfinder wing as a calibration model. In the second part, it is shown that for selected flow conditions a good agreement is obtained between stability analysis based on experimental and numerical data. In the third part the correlation of experimental transition locations to critical N-factors is summarized for ETW Test Phases I and II. In the fourth part numerical analysis and experimental data are used complementarily.
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.
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