  This study numerically explores the flow physics associated with nanosecond
pulsed plasma actuators to control shock-wave induced boundary-layer
separation. By using two actuators, parallel and canted with respect to the
main flow direction, a previous experiment suggested the actuator worked in two
ways: boundary layer heating and vorticity production. The heating effect was
enhanced with the parallel electrode and made the separation stronger, while
the canted electrode produced vorticity and suppressed the separation due to
the momentum transfer. Because the detailed physics is still unclear, a
numerical investigation is undertaken with a large eddy simulation and an
energy deposition model for the actuator. The flow without the actuation
corresponds to the experimental observation, indicating the calculation
successfully resolves the separation. With the actuation, as with the
experiment, the calculation successfully demonstrates definite difference
between the parallel and canted electrodes: the parallel electrode causes
excess heating and increases the separation, while the canted electrode leads
to a reduction of the separation, with a corresponding thinning of the boundary
layer due to the momentum transfer. The counter flow created by the canted
actuator plays an important role in the vortex generation, transferring
momentum to the boundary layer and, consequently, mitigating the separation.
