Numerical simulations of laser energy deposition in air are conducted. Local thermodynamic equilibrium conditions are assumed to apply. Variation of the thermodynamic and transport properties with temperature and pressure are accounted for. The flow field is classified into three phases: shock formation; shock propagation; and subsequent collapse of the plasma core. Each phase is studied in detail. Vorticity generation in the flow is described for short and long times. At short times, vorticity is found to be generated by baroclinic means. At longer times, a reverse flow is found to be generated along the plasma axis resulting in the rolling up of the flow field near the plasma core and enhancement of the vorticity field. Scaling analysis is performed for different amounts of laser energy deposited and different Reynolds numbers of the flow. Simulations are conducted using three different models for air based on different levels of physical complexity. The impact of these models on the evolution of the flow field is discussed.
Bibliographical noteFunding Information:
This work is supported by the United States Air Force Office of Scientific Research under grant FA-9550-04-1-0064. Computing resources were provided by the Minnesota Supercomputing Institute, the San Diego Supercomputing Center, and the National Center for Supercomputing Applications. We are thankful to Dr Noma Park for useful discussions.