Showing papers by "Terrence W. Simon published in 2009"

Computational modeling of a segmented-involute-foil regenerator for stirling engines

Abstract: A microfabricated, segmented-involute-foil regenerator was numerically investigated using the Fluent commercial software under both steady- and oscillatory-flow conditions and using two- and three-dimensional numerical simulations. Steady-state simulations were performed for Re = 50-2000. The oscillatory-flow conditions were performed for Re max = 50 and Re ω = 0.229, with the hot end at 310 K and the cold end at 293 K. For the steady-state three-dimensional simulation, both the local friction factor and the local mean Nusselt numbers started to depart from the two-dimensional simulation values upon entering the second layer. At the entrance of every layer, the forced reorientation of the flow results in small rises of both the friction factor and the mean Nusselt number, with subsequent decrease as the flow settles into the new layer. As for the oscillatory-flow simulations, the two-dimensional model was used to study the effects of changing 1) the oscillation amplitude and frequency, 2) the thermal contact resistance between layers, and 3) the solid material. The effects of these parameters on the total regenerator heat loss (convection and conduction) were documented and are expected to be a useful tool for further development of Stirling engine regenerators.

Separation control using plasma actuator: Simulation of plasma actuator

Abstract: Simulation of a dielectric barrier discharge (DBD) plasma actuator and a numerical model for simulating air chemistry are briefly intr oduced Results from the model are presented for plasma discharge under positive and negative nanosecond pulse operation Computed space-integrated forces for the two cases are compared Preliminary results from simulations of a new actuator design for surface ch arge control are presented I Introduction Plasma actuators are known to be effective in promo ting boundary layer reattachment on airfoils A sch ematic of an actuator is shown in Fig 1 Plasma generated on the actuator geometry is known to produce time-ave raged thrust in the direction of the air flow When embedded in an airfoil surface and properly operated, the actua tor can induce turbulence in the fluid flow causing earlier transi tion to turbulence and making the airfoil more effi cient Simulations have been performed to understand the working of plasma actuators A lumped element electr ical circuit model was developed in order to understand the spatial and temporal behavior of the plasma dis charge 1 The resultant force from the actuator is seen as a func tion of applied voltage amplitude and frequency Mo re detailed fluid models for plasma were developed for two dimensional simulations of the actuator geometry 2 3 The duration of the simulated discharge is in the range of micro seconds The thrust produced by the actuator is see n to be an electro-hydrodynamic force associated with momentum transfer from the charged plasma species to the ne utral particles 4 However, these models used time steps that were t oo large to resolve the plasma processes correctly The DBD was modeled for an AC sine wave 5 with a frequency of 1000 kHz It was deduced that the negative ions rendered the momentum transfer inefficient by actin g in the direction opposite to the positive ions, w hich, having larger densities, are primarily responsible for the momentum transfer Font et al 6 were the first to model a streamer in the nanosecond time scale using the Particle-in- Cell technique They found that the presence of neg ative ions did not change the force producing characteristics alth ough it reduced the actuator efficiency The downst ream force was found to be 20 times higher than the upstream f orce and force was seen to be a function of exposed electrode thickness Likhanskii et al simulated plasma for na nosecond sine waves and found that negative ions to play a role in producing the downstream directed force during the negative half cycle 5