Coupling of an Unsteady Aerodynamics Model with a Computational Fluid Dynamics Solver

Abstract

Coupling of an unsteady aerodynamics model with a computational fluid dynamics solver. Momentum source methods are an efficient means of representing airfoils in Navier-Stokes CFD simulations. Momentum source terms are added to the Navier-Stokes equations instead of resolving the solid boundary of the airfoil with a mesh. These source terms are calculated using an aerodynamics model. This approach is useful where the overall performance and midto far-field influence of a wing or rotor are desired and details of the flow field near the blade are not the objective of the simulation. One example is simulation of rotorcraft operations where the objective may be to assess an operation's feasibility in terms of control margins, rather than to inform rotor design decisions. Coupling an aerodynamics model to a CFD solver is straightforward in cases where the airflow relative to the blade is steady. Unsteady conditions require an unsteady aerodynamics model, complicating the coupling with the CFD solver. A coupling method is proposed whereby the incident velocity is extracted from the CFD solution and corrected using a theory based approximation for the unsteady induced velocity. The steady-state momentum source method is demonstrated for 2D and 3D simulations and the unsteady coupling method is validated against experiments on a pitching airfoil and verified for blade-vortex interactions. The unsteady coupling method enables meaningful incident velocities to be extracted from unsteady flow-fields, as shown by agreement with experiments and simulations using analytical expressions for the incident velocity in place of the CFD solver.

Rotorcraft and Ship Airwakes Simulations Using Immersed Boundary Method

“…The IBM is a discrete forcing approach based on the method of Jasak et al [7], and a wall function implemented into the IBM code uses the S-A analytical wall formula [1,15]. In the ASM [9], the flow around a three-dimensional finite wing is approximated by a linear summation of flows around spanwise sections by the lifting-line theory, and the aerodynamic properties of each two-dimensional airfoil are calculated from an aerodynamic coefficient table using the effective angle of attack α eff [9,11]. Then, a load F corresponding to α eff is obtained from the aerodynamic coefficient table, and this load is used to calculate the momentum source field S:…”

“…where g c (x c ) and g n (y c ) are the chordwise and chord-normal source distribution functions (refer to [9] for their definitions).…”

“…The coupled IBM-ASM solver aims to provide efficient and accurate computations of the high Reynolds number flow around multiple vertical take-off and landing (VTOL) vehicles operating in the neighbourhood of a landing platform such as a ship, oil rig or building. In this method, rotating rotor blades are represented by an unsteady actuator surface [9] while the IBM with a wall function enforces a wall boundary condition of the rest of the solid objects onto the flow field. This non-body-conformal mesh approach allows a fully automated meshing of complex geometries and moving body simulations on a simple Cartesian mesh without a mesh deformation.…”

Minimum Parameters Learning-Based Dynamic Surface Control for Advanced Aircraft at High Angle of Attack

“…Hence, it is impossible to obtain the accurate aerodynamic model at high angle of attack from the conventional aerodynamic model. How to obtain aerodynamic data at high angle of attack and establish accurate unsteady aerodynamic model is the primary challenge for advanced fighter during the post-stall maneuver [3], [4].…”

Aerodynamic Characteristics of Helicopter with Ducted Fan Tail Rotor in Hover under Low-Speed Crosswind

“…International Journal of Aerospace Engineering Therefore, the actuator methods provide advantages in evaluating the overall flow characteristics and aerodynamic performance of helicopters under various flight conditions with computational efficiency [19,20].…”