Undeflected Common Research Model (uCRM): An Aerostructural Model for the Study of High Aspect Ratio Transport Aircraft Wings

Abstract

Since its introduction, the NASA Common Research Model (CRM) has served as a useful aerodynamic benchmark for CFD-based drag prediction and aerodynamic design optimization. The model was originally conceived as a purely aerodynamic benchmark and as such, the wing geometry corresponds to the deflected shape at the nominal 1 g flight condition. There has been growing interest in extending this model for aeroelastic studies. Due to its predefined deflection, the model is not suitable for aeroelastic analysis and design. To address this issue, we define an undeflected Common Research Model (uCRM), which includes the outer mold line geometry of the undeflected wing and the corresponding internal wingbox structure. The developed aeroelastic model achieves the flying shape of the CRM under the nominal flight condition. The topology of the wingbox is designed to be similar to that of a Boeing 777. The jig shape was obtained through an inverse design procedure where the objective was to minimize the difference between the 1 g aerostructurally deflected shape and the CRM. The original CRM has an aspect ratio of 9, so we refer to this model as the uCRM-9. Additionally, since modern transport aircraft are trending toward higher aspect ratio wing designs to reduce induced drag, and therefore fuel burn, there is a need for a higher aspect ratio variant of this model to assess next-generation wings. This variant, the uCRM-13.5, has a larger aspect ratio of 13.5 and is defined through a multipoint aerostructural optimization subject to buffet onset constraints. These models provide a publicly available benchmark for aeroelastic wing analysis and design optimization studies.

How Certain Physical Considerations Impact Aerostructural Wing Optimization

“…Because SNOPT is not freely available to the public, the cases included in the Waspy repository use Scipy's SLSQP [44] method. Figure 5 shows the optimized skin-thickness distributions for the uCRM-9 wing from OpenAeroStruct compared to the results from high-fidelity (RANS CFD and shell-element FEM) optimization [13]. We see reasonable agreement in the outboard part of the wing, but there are significant differences at the root.…”

“…This is valid for small RC-scale aircraft and some stunt planes, but not for the majority of transport aircraft. Chauhan and Martins [7] implemented a wingbox model for a more accurate representation of typical transport-aircraft wing structures and found that the optimized fuel-burn and structural-weight results matched high-fidelity results [13] within 10% for the undeflected Common Research Model (uCRM-9 [5]) wing.…”

“…We use the uCRM-9 geometry [13,5] for the long-range transport wing. The uCRM-9 is based on the CRM [38], but modified to remove the flying-shape deflections.…”

“…Coupling VLM codes for the aerodynamics and FEM codes for the structure allows for rapid optimization studies that consider aerodynamic and structural trade-offs for a multidisciplinary design optimization (MDO). Even though VLM models and simplified FEM models may not be able to capture as much physics and detail as higher-order methods such as RANS-based computational fluid dynamics (CFD) and detailed FEM models [7,13], their low cost enables broader design studies that capture major trends with significantly lower computational cost. In this paper, we take advantage of the low cost of VLM and FEM codes to carry out multiple design studies with varying considerations (21 optimization problems in total) to understand different trade-offs.…”

Active Flutter Suppression Controllers Derived from Linear and Nonlinear Aerodynamics: Application to a Transport Aircraft Model

“…Although researchers have successfully integrated higher-order CFD solvers into computational aeroelastic models (Refs. 12,13), it is still considered to be a challenge because of the high computational cost [14], particularly for unsteady simulations. Because of this, there are only a handful of dynamic aeroelastic analyses done using higher-order CFD solvers, and most of those are done using simple geometries.…”