Propulsor crashback is an off-design operating condition where a propulsor rotates in the reverse direction to yield negative thrust. Crashback is characterized by the interaction of the free stream with the reverse flow generated by propulsor rotation. This causes a highly unsteady vortex ring which leads to flow separation and unsteady forces and moments on the blades. Large eddy simulation (...

Unsteady flow models of wings and airfoils have been studied to understand the aerodynamic performance of natural flyers and provide improved maneuverability for micro aerial vehicles (MAVs). Vortex methods have been extensively applied to reduce the dimensionality of these aerodynamic models, based on the proper estimation of the distribution and evolution of the vortices in the wake. In such ...

We apply the phase-reduction analysis to examine synchronization properties of periodic fluid flows. The dynamics of unsteady flows are described in terms of the phase dynamics reducing the high-dimensional fluid flow to its single scalar phase variable. We characterize the phase response to impulse perturbations, which can in turn quantify the influence of periodic perturbations on the unstead...

The paper presents an adjoint based approach for determining global error in the time domain that is relevant to scalar outputs computed as functions of the unsteady flow solution. The algorithm is derived for the unsteady Euler equations and takes into account the effect of dynamic meshes. Two primary components of the total error are specifically identified, namely, the error due to temporal ...

This paper presents an Euler and boundary-layer method capable of unsteady flow and aeroelastic simulations. An integral boundary-layer solver is coupled with an Euler solver in a “semi-inverse” manner. For the inviscid part, approximate wall boundaryconditions are implemented on non-moving mean chord positions, whereas the full nonlinear Euler equation is solved in the field for accurate resol...

Time-dependent flows of a Newtonian fluid through periodic arrays of spheres were simulated using the lattice-Boltzmann scheme. By applying a constant body force per unit mass to the fluid, a steady background fluid flow through the array of stationary spheres was first established. Subsequently, a small-amplitude perturbation to the body force, which varied periodically in time, was added and ...

Preconditioning methods have become the method of choice for the solution of flowfields involving the simultaneous presence of low Mach number flow and transonic flow regions. It is well known that these methods are important for insuring accurate numerical discretization as well as convergence efficiency over various operating conditions such as low Mach number, low Reynolds number and high St...