Research On Microjet Used For Flow Vector Active Control

A new method for active control of flow field appears. It is the so-called microjet technology. Its fundamental principle is based on the MEMS, the chaotic theory and non-linear complicated system theory. The mechanism of active flow direction control is the microjet's microscale disturbance coupling with the macroscale's flow through collective interaction. The microjet is a zero net mass-flux and doesn't require internal source of jet fluid. Its control system is simple, light and little energy consumed. Microjet is superior to conventional jet. So this dissertation studies the microjet flow field and the synthetic flow field of the microjet and the mean flow by numerical simulation. The main research results in the dissertation are as follows:1. According to the characteristics of the microjet and the synthetic flow field, the unsteady, two/three dimensional, compressible N-S equations were used for the flow field simulation. Time-accurate solutions to N-S equations were obtained by the implicit approximately-factored(AF) finite-difference algorithm. Newton-like subiterations were used within a time step to reduce errors due to factorization, linerization and explicit application of boundary conditions. Numerical fluxes considered in the explicit portion of the algorithm were evaluated by an implicit high-order compact scheme to augment stability. Meanwhile, an implicit high-order compact numerical filter was used.2. The laminar/turbulence models were used to simulate the single microjet flow field. The result shows the periodic characteristics of microjet flow field including vortex pair evolution, immigration and dissipation process. The synthetic flow field of two adjacent microjet actuators and its evolvement with time, as well as different working frequencies and relative phase angles were numerically simulated. The "low pressure closed recircular flow region" was analyzed to explain the characteristics of the synthetic flow field.3. The 3D simulation result shows characteristics as well as creating, developing and dissipation process of the microjet. The results show good agreement withexperimental results. The numerical study reveals the spanwise instability of vortex pairs, resulting in the breakdown of the coherent vortex structure. Especially the secondary vortex is also captured.4. Vectoring of a primary jet with a single or two adjacent microjets in a pull mode was numerically investigated. The result shows the primary jet can be vectored and trends towards the microjet actuators. Analysis indicates the "low pressure closed reticular flow region" results in the non-equilibrium of pressure along the primary jet's orifice. To obtain as large vectoring angle as possible, the optimal ranges of angles, frequencies, velocity amplitudes, and distances from the microjet actuator to the primary jet exit were discussed. The relationship between the vectoring angle of the primary jet and the phase-difference of two adjacent actuators was analyzed.5. The modification of the aerodynamic force performance on a 2D cylinder by use of microjet was numerically simulated. The result shows that the pressure distribution on the cylinder and the wake are modified, and the separate flow partially is attached to the surface again.