Control of Karman Vortex Street By Using Plasma Actuators

A mathematical model for unsteady electro-and aerodynamic processes in the presence of a plasma actuator has been elaborated through physical modeling of the dielectric barrier discharge.A specialized computational fluid dynamics package has been developed accordingly in order to calculate steady and unsteady laminar and turbulent flows.For the numerical simulation of the dielectric barrier discharge,in particular,two equations have been added to the Navier-Stokes equations and solved.They describe the distribution of the applied voltage and the charged particles density.The impact of the plasma actuator on air has been accounted for through the Lorentz force,included as a source term in the momentum balance equation.The system of governing equations for the considered hydrodynamics and electrodynamics has been written in an arbitrary curvilinear coordinate system in dimensionless form and integrated in the framework of a finite volume method.A TVD scheme with a third-order ISNAS flow limiter has been chosen for the convective terms approximation.The obtained block-matrix system of linear algebraic equations has been solved by the generalized minimal residual(GMRES)method with ILU(k)preconditioning.Using this approach,the occurrence of a propulsion force,emerging as a result of the action of plasma actuators on a cylinder in quiescent air,has been investigated.The possibility to mitigate the cylinder drag coefficient with the help of the plasma actuators,due to the ensuing suppression of the Karman vortex street,has been demonstrated.

Computational Simulation of Turbulent Flow Around Tractor-Trailers

A method to evaluate the properties of turbulent flow in proximity to the vehicle and close to the ground surface has been elaborated.Numerical simulations have been performed on the basis of the Unsteady Reynolds-averaged Navier-Stokes equations(URANS)written with respect to an arbitrary curvilinear coordinate system.These equations have been solved using the Spalart-Allmaras differential one-parametric turbulence model.The method of artificial compressibility has been used to improve the coupling of pressure and velocity in the framework of a finite volume approach.Time-averaged distributions of pressure fields,velocity components,streamlines in the entire area and near the tractor-trailer,as well as integral and distributed characteristic parameters(such as coefficients of pressure,friction and drag force)are presented.According to our results,the turbulent flow accelerates in the area of the tractor cabin and in the gap between surfaces.Above the driver’s cabin,a pressure drop occurs due to a sharp acceleration of flow in this area.Downstream,pressure is restored and becomes almost constant in proximity to the edge of the trailer.The dimensions of the separation area exceed the length of the transport system several times.Though agreement with experimental results is relatively limited due to the two-dimensional nature of the numerical simulations,the present approach succeeds in identifying the main physical effects involved in the considered dynamics.It might be used in future studies for initial approximate assessments of the influence of the vehicle shape on its aerodynamic characteristics.