Progress Toward Efficient Laminar Flow Analysis and Design

Abstract

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.

Development and Application of Transition Prediction Techniques in an Unstructured CFD Code (Invited)

“…For the application of the LST-based e N method within a large CFD system it is possible to either apply an automated linear stability code [22] or database methods of different approximation levels [27][28][29][30][31][32][33] so that an automatic and autonomous execution of transition prediction can be carried out during the ongoing run of a CFD simulation. At the same time, information and data about the stability behavior of the laminar boundary layer from the point of neutral stability (critical point) up to the point where the critical N-factor is reached (point of transition onset) are calculated and can be made available to the user.…”

Aerodynamic Shape Optimization for Natural Laminar Flow Using a Discrete-Adjoint Approach

“…4 Examples of transition criteria based on a transition onset function are Michel, Granville, H−Re x , Abu-Ghannam and Shaw, Gleyzes-Habiballah, and Arnal-Habiballah-Delcourt. 18,19,22 These methods have been classified as "simpler" or "analytical" transition criteria.…”

Building a Practical Natural Laminar Flow Design Capability

“…As an alternative, the MATTC method has been shown to provide reasonable estimates of transition location in 2-3 orders of magnitude less time. The code uses semiempirical functions whose coefficients can be calibrated based on LASTRAC results for the baseline or initial target pressure distributions for improved accuracy 11 . In addition, a new feature has been added to MATTC to predict leading edge CF peak heights as the original version did not predict CF growth well for our NLF pressure distributions.…”