Hi

Based on the movement of the hexacopter in a free domain you should consider a huge domain around the hexacopter(you can find it in other papers). Your boundary conditions are inlet velocity by considering the relative velocity (hexacopter velocity and the wind velocity), Symmetry boundary conditions for sides and down, and a pressure outlet for the end of the domain. Besides note, the MRF is acceptable for blade rotation.

Even a good simulation means nothing if it's not correlated to at least analytical analysis. The best would be a three prong approach, and correlating results between numerical, analytical and experimental methods. Air flow around a multi-rotor could lead to very complicated blade interactions, you can get weird results and you need to validate them by at least analytical methods if experimentation is not possible. Do at least disk actuator analysis, that will give you a maximum theoretical possible performance. If your simulation results are better, then something must be wrong.

In my work with regard to the question --i found the "Lift generated by the rotating helicopter blades was a nonlinear function of static cg locations along a radius vector of the mutlple helicopter blades --- resulting in a linearized system state of order 10. This "stater variable model was "unstable and as such the only way to stabilize the system was through active pilot controls -- see papers available on ResearchGate.

Good luck on your work

Respectfully, Al Fermelia

Oluwasheyi Oyename For a forward flight configuration, the cyclic pitch of a rotating rotor (disk) tends to tilt towards the flight direction. You must establish the proper helix angle (phi), which is the angle between the flight path and the horizontal plane parallel to the ground. Thus the boundary of flow towards the tilted rotor (disk) is determined by the computed geometric pitch angle (beta), helix angle (phi), and angle of attack (alpha). The amount of (forward)Thrust would be equal to (0.5) x (density of air, 1.25 kg/m^3) x (Velocity^2) x (maximum blade chord at radius r, refer to the drawing image attachment)x(rotor disk diameter) x ((coefficient of lift, "cl" x sin phi) + (coefficient of drag, "cd x Cos phi)). You may assign a design angle of attack (alpha), geometric pitch angle (beta), and helix angle (phi) values to get your desired value of Thrust; to get the corresponding cl and cd from a "Cl versus Velocity graph" of your chosen NACA airfoil (say NACA 6612 airfoil, found in the internet, see sample attached file). Even for multi-rotor, you may simulate only 1 rotor (disk), the resulting values of parameters after simulation would be the same for all other rotors. If you want to simulate your whole system of multi-rotor, make a 3D model of it on solidworks and get it on the "X-plane Simulator" of an (OADsoftware).