We examined the role of Streptococcus pyogenes two-component response regulators (SptR) in expression of Mga and the Mga-regulated gene emm. Both serotype M6 and serotype M1 mutants in 12 of the 13 identified sptR genes exhibited levels of emm transcripts and Mga protein comparable to those of the wild type during exponential and stationary phases of growth. Thus, temporal control of these virulence genes does not require Spt response regulators.

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Synthetic jet actuators are utilized on a nominally 'free' yawing axisymmetric model to induce localized flow attachment over the body's aft end and thereby alter the dynamic model orientation. The model is supported by a vertical thin steel wire that passes through the model that undergoes natural oscillatory response to the oncoming flow. Hybrid fluidic actuation is effected using two independently driven aft-facing jet actuators that emanate from narrow, azimuthally-segmented slots, centered symmetrically on the opposite ends of the yawing plane, and placed on a circular tail end that extends into a Coanda surface. The body motion response is measured using a laser vibrometer, and the aft coupled body/flow dynamics is characterized using planar PIV. Continuous actuation schemes, independent of model motion, and the respective aerodynamic responses are investigated with 'open loop' fluidic control. In addition, a PID controller is developed to effect 'closed loop' fluidic control with optimally timed synthetic jet operation dependent on model motion. Fluidic actuation demonstrates up to 60% suppression of natural yaw oscillations, and can impose directional preference with open loop control. The closed loop control results in more prominent yaw oscillation suppression of about 90%, directional preference, or oscillation amplification, displaying a large potential for directional control authority of free flight aerodynamic bodies.

The present experiments focus on active fluidic control of the aerodynamic forces and moments of an axisymmetric bluff body platform in time-periodic sinusoidal pitch oscillations at reduced frequencies 0 < k < 0.259. The platform is wire-mounted on a six degree of freedom traverse where each of the eight support wires is individually controlled by a servo motor with an integrated in-line load cell for feedback control of the platform's motion. The aerodynamic forces and moments on the platform are manipulated by controlled interactions of an azimuthal array of synthetic jet actuators on its aft segment with the local cross flow to induce partial (azimuthally-segmented) flow attachment that is coupled with vectoring of its nearwake. The actuation-induced forces and moments can either increase or diminish the corresponding pitchinduced baseline aerodynamic forces and moments. These actuation effects are exploited for open-loop control to suppress or augment the pitch-induced moment, and effect robust (in excess of 50%) control authority over a broad range of oscillation frequencies (up to reduced frequency of 0.259) that are suitable for trajectory stabilization and steering in free-flight.

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Abstract:Flapping flight is an increasingly popular area of research, with applications to micro-unmanned air vehicles and animal flight biomechanics. Fast, but accurate methods for predicting the aerodynamic loads acting on flapping wings are of interest for designing such aircraft and optimizing thrust production. In this work, the unsteady vortex lattice method is used in conjunction with three load estimation techniques in order to predict the aerodynamic lift and drag time histories produced by flapping rectangular wings. The load estimation approaches are the Katz, Joukowski and simplified Leishman-Beddoes techniques. The simulations' predictions are compared to experimental measurements from wind tunnel tests of a flapping and pitching wing. Three types of kinematics are investigated, pitch-leading, pure flapping and pitch lagging. It is found that pitch-leading tests can be simulated quite accurately using either the Katz or Joukowski approaches as no measurable flow separation occurs. For the pure flapping tests, the Katz and Joukowski techniques are accurate as long as the static pitch angle is greater than zero. For zero or negative static pitch angles, these methods underestimate the amplitude of the drag. The Leishman-Beddoes approach yields better drag amplitudes, but can introduce a constant negative drag offset. Finally, for the pitch-lagging tests the Leishman-Beddoes technique is again more representative of the experimental results, as long as flow separation is not too extensive. Considering the complexity of the phenomena involved, in the vast majority of cases, the lift time history is predicted with reasonable accuracy. The drag (or thrust) time history is more challenging.

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