Control surface modeling: analysis of unsteady effects of spanwise gaps using linearized frequency-domain solvers

Kurzfassung

Control surface deflections induce unsteady aerodynamic loads that are essential for aircraft performance and stability assessments, yet their accurate prediction remains challenging and computationally expensive due to complex flow phenomena around geometric discontinuities.

This study evaluates the capability of linearized frequency-domain (LFD) methods to model these unsteady effects, with particular focus on the aerodynamic influence of spanwise gaps between lifting and control surfaces. Two LFD solvers are compared: the established LFD-TAU and the more recent LFD-CODA—the frequency domain variant of the CFD software of ONERA, DLR, and Airubs (CODA). A major advantage of LFD-CODA is its fully differentiated overset-mesh capability, which enables the investigation of configurations with spanwise gaps using LFD. Such analyses are not possible with LFD-TAU, as its overset-mesh implementation has not been linearized.

Using NASA’s Benchmark Active Controls Technology model, this work examines both clean-wing and gap-resolved configurations. The results demonstrate good agreement with experimental data for mean and unsteady pressure distributions, while revealing the significant influence of spanwise gaps on local unsteady aerodynamic characteristics, especially in the control surface vicinity. Sensitivity studies identified the control surface rotation strategy as a critical factor for accurate predictions in clean-wing configurations, whereas mesh deformation algorithms showed negligible impact on global aerodynamic coefficients. An important observation was the relatively weak amplitude effects for control surface deflection amplitudes up to 4◦ in the transonic test cases examined, suggesting that LFD methods may be applicable beyond the usual very small control-surface deflection angles.

These findings establish LFD as an accurate and efficient tool for rapid unsteady aerodynamic assessments of the impact of control surface deflections.