, "Reduced order unsteady aerodynamic modeling for stability and control analysis using computational fluid dynamics" (2014
Contents
ABSTRACTRecent advances and challenges in the generation of reduced order aerodynamic models using computational fluid dynamics are presented. The models reviewed are those that can be used for aircraft stability and control analysis and include linear and nonlinear indicial response methods, Volterra theory, radial basis functions, and a surrogate-based recurrence framework. The challenges associated with identification of unknowns for each of the reduced order methods are addressed. A range of test cases, from airfoils to full aircraft, have been used to evaluate and validate the reduced order methods. The motions have different amplitudes and reduced frequencies and could start from different flight conditions including those in the transonic speed range. Overall, these reduced order models help to produce accurate predictions for a wide range of motions, but with the advantage that model predictions require orders of magnitude less time to evaluate once the model is created.Published by Elsevier Ltd.
A new approach for computing the unsteady and nonlinear aerodynamic loads acting on a maneuvering aircraft is presented based on linear and nonlinear indicial response methods. The novelty of this approach relies on the use of a grid motion technique for CFD calculation of response functions and the development of a time-dependent surrogate model that fits the relationship between flight conditions (Mach number and angle of attack) and responses calculated from a limited number of simulations (samples). The reduced-order model, along with the surrogate model, provides a means for rapid calculation of response functions and predicting aerodynamic forces and moments during maneuvering flight. The maneuvers are generated using a time-optimal prediction code, each covering a different range of angle of attack and motion rates. The side-slip angle ranges from −5 • to 5 • for all maneuvers, and the model assumes that the lateral aerodynamics is linear with side-slip angle over this range. Results presented show that the aircraft studied in the current paper exhibits highly nonlinear roll moments even at low angles of attack which the linear model fails to predict. The results of the new model provide some evidence that, for a certain range of input parameters, in certain maneuvers considered, the predictions match quite well with URANS CFD predictions. The models were at least better than traditional quasisteady predictions. However, for aircraft maneuvering at high angles of attacks, discrepancies are found in lateral coefficients between the model and CFD. At these conditions, the lateral airloads become highly nonlinear with side-slip angle and the model fails to predict these effects. Also, the results show that the CFD calculation of response functions in the high angle of attack flight regime remains a challenging task.Published by Elsevier Masson SAS.
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