This study is a collaborative effort within the NATO Science & Technology Organization, bringing together multiple institutions to advance reduced-order modeling. Aerodynamic reduced-order models were developed using two pseudorandom binary sequence (PRBS) training maneuvers, where the angle of attack and pitch rate varied in a periodic, deterministic manner with white-noise-like properties. The first maneuver maintained a constant Mach number of 0.85, while the second varied Mach from 0.1 to 0.9. The test case involved a generic triple-delta wing, simulated using the DoD HPCMP CREATE™-AV/Kestrel/Kestrel tools. Prescribed-body motion was used to vary input parameters under given freestream conditions. The resulting models predicted static and stability derivatives across different angles of attack and Mach numbers. They were also used to predict aerodynamic responses to arbitrary motions, including sinusoidal, chirp, Schroeder, and step inputs, showing good agreement with full-order data. Additionally, models predicting surface pressure accurately captured upper surface pressures across different spanwise and chordwise locations for both static and dynamic conditions.

Efficient input data generation for reduced-order model applications to accurately predict aerodynamic performance and stability characteristics over a large part of a fighter aircraft’s flight envelope is a major challenge. In this paper, aerodynamic reduced-order models are created from two pseudorandom binary sequence (PRBS) training maneuvers. During these maneuvers, the angle of attack and pitch rate change in a periodic and deterministic manner which is characterized by white-noise-like properties. Typical PRBS signals include sudden input variations between two distinct values, such as minimum and maximum angles of attack. However, the signals used in this paper were modified to have the step changes to depend on the simulation time. In the first motion, the aircraft undergoes a signal at a constant Mach number of 0.85. In the second motion, the Mach number varies in an optimized manner from 0.1 to 0.9. The test case is a generic triple-delta wing configuration. Simulations were run using the DoD HPCMP CREATE^RM-AV/Kestrel simulation tools. A prescribed-body motion was used to vary input parameters under given freestream conditions (Mach number and angle of attack). Different reduced-order methods were applied, that comprise regression, feed-forward neural network and auto-regressive surrogate modeling techniques to predict integrated force and moment coefficients and a proper-orthogonal decomposition based neural network approach for surface pressure prediction. Once models of integrated forces and moments were created, they were used to predict static and stability derivatives at different angles of attack and Mach numbers. Models were then used to predict aerodynamic responses to arbitrary motions including pitch sinusoidal, chirp, Schroeder, and step. Model predictions were compared with actual CFD data. Overall, a good agreement was found for all models. Models to predict surface pressure data were also able to accurately predict the upper surface pressure data at different spanwise and chordwise locations at different angles of attack for both static and dynamic runs.

Within the NATO STO AVT-251 Task Group a generic Unmanned Combat Air Vehicle (UCAV) planform is redesigned based on requirements derived from parts of the flight envelope of the defined mission. Because of the lambda-shape planform and associated flow phenomena including shocks and vortices, the aerodynamic design process relies heavily on high-fidelity CFD predictions. This enables accurate prediction of flight dynamics and any potential issues early in the design process. The flight dynamics model would be based on a reduced order model (ROM) derived from CFD calculations. This work investigates the creation of a ROM using nonlinear indicial response functions. The response functions are obtained using a grid motion approach that separates the effects of angle of attack and pitch rate. This approach is followed using three different CFD codes from various organizations: ENSOLV at the Netherlands Aerospace Centre, USM3D at NASA Langley Research Center, and Kestrel at the United States Air Force Academy. The ROM predictions were tested with a manoeuver resembling a low speed pull-up. The predictions are found to be sensitive to the quality of the steady state solutions from which step response calculations were started, as well as the convergence of the step response calculations themselves. Nevertheless, the indicial response method can provide accurate predictions including transient effects, and as such is a powerful method for building ROMs.