FOIST: Fluid–object interaction subcomputation technique

Abstract

SUMMARYOur target is to develop computational techniques for studying aerodynamic interactions between multiple objects. The computational challenge is to predict the dynamic behavior and path of the object, so that separation (the process of objects relatively falling or moving away from each other) is safe and effective. This is a very complex problem because it has an unsteady, 3D nature and requires the solution of complex equations that govern the fluid dynamics (FD) of the object and the aircraft together, with their relative positions changing in time.Large-scale 3D FD simulations require a high computational cost. Not only must one solve the timedependent Navier-Stokes equations governing the fluid flow, but also one must handle the equations of motion of the object as well as the treatment of the moving domain usually treated as a type of pseudo-solid. These costs include mesh update methods, distortion-limiting techniques, and remeshing and projection tactics. To save computational costs, point force calculations have been performed in the past. This paper presents a hybrid between full mesh-moving simulations and the point force calculation. This mesh-moving alternative is called FOIST: fluid-object subcomputation interaction technique.

Correct implementation of the fluid–object interactions subcomputation technique (FOIST)

“…Yet, in each computation, the possible explanations given for these significant discrepancies do not include the omission of the terms associated with using a non-inertial reference frame. We do not see in [17] any mention of those missing terms.…”

“…On the other hand, if the reference frame is an inertial reference frame, then there would be no such additional terms, but a correct FOIST implementation has to be based on a moving-mesh method. In the computations reported in [17], the reference frame in each subcomputation is attached to the moving object and therefore it is a non-inertial reference frame, but the governing equations of fluid mechanics used in the computations do not include the additional terms associated with using a non-inertial reference frame. Therefore the computations reported in [17] are not based on a correct implementation of the FOIST.…”

Three-Dimensional Aerodynamic Simulations of Jumping Paratroopers and Falling Cargo Payloads

“…III.A changing only the boundary condition on the aircraft. It is now given a slip condition allowing the fluid particles to flow along the surface of the aircraft, thereby eliminating the boundary layer and the low drag problem as before [19] (Fig. 16).…”

“…Because gravity dominates here, a slip formulation should have a smaller effect than it did in the paratrooper simulation. Still, for such speeds, we may apply a slip boundary condition on the aircraft [19] to increase the drag felt by the cargo and view the improvement on the trajectory.…”

“…Here, the same separation problem of the jumping paratrooper exiting from the cargo aircraft is simulated with slip conditions implemented implicitly [19]. The boundary conditions are the same as stated in Sec.…”