Aerodynamic Control of Coupled Body-Wake Interactions

Abstract

The unsteady interactions between fluidic actuators and the cross flow over the aft end of a moving bluff body are exploited for modification of the global unsteady aerodynamic loads in wind tunnel experiments using a moving axisymmetric model. The model moves in combined pitch and yaw which is designed to mimic the natural unstable motion of a similar airborne platform in the absence of roll. Actuation is effected using an azimuthallysegmented array of four aft-facing synthetic jet modules around the tail end of a model, and motion is effected by eight mounting wires that are attached to servo motors for timedependent, six degrees of freedom motion along a prescribed trajectory. Enhancement and suppression of stabilizing aerodynamic loads on the model are each investigated using coupled force and moment measurements and stereo particle image velocimetry in the near wake, at reduced frequencies of up to 0.26. The present measurements show significant suppression (up to 80%) and augmentation (up to 40%) of the platform's motion-induced aerodynamic forces or moments with concomitant controlled deflection and decoupling of the near-wake from the motion of the body. The present investigations show that the effects of actuation on the near wake of the body are comparable to the effects of its baseline unstable pitch and yaw motion and therefore can be used to induce aerodynamic loads that cancel or enhance the baseline loads to effect dynamic steering and stabilization.

Aerodynamic Flow Control of Wake Dynamics Coupled to a Moving Bluff Body

“…The next four modes (Figures 7c-f) have a similar structure with a central velocity contribution and two dominant external contributions which are attributed to fluctuations in the shear layer. The seventh mode is a two lobe structure which has a preferential shedding in the diagonal direction which is similar to a mode observed in prior studies on this model (Figure 6a in Lambert et al, 2016a) when the model was in a fixed stationary centered position, where the diagonal directional preference was attributed to the preferential shedding off of the aft end model due to the actuators and Coanda surface.…”

“…This trend is consistent for the streamwise vorticity, x , where both the horizontal and vertical centerlines show similar traces, each with an inner-wake region full of rapidly oscillating, low-amplitude concentrations of vorticity, and the outer-wake having a weak band structure (Compare Figures 15d and h). It is noted that the structure of the wake with closed-loop hold-center actuation is also in excellent agreement with low-speed stereo PIV velocity and vorticity time traces measured on a static centered model at a downstream location of x/R = 2 by Lambert et al (2016a). In the presence of pitch amplification control (Figures 15i-p), the original oscillations over the wake deficit are horizontally reduced (Figure 15i) while new vertical oscillations are introduced with a larger magnitude than the unactuated yaw oscillations (compare Figure 15m with Figure 6e).…”

“…The interrogation region is placed in the y-z plane at x m /c = 0.9 (or 0.25D downstream of the aft end of the model), spanning 1.8D in y and in z (y = ±1.8R, and z = ±1.8R, centered about the streamwise axis of the model's gimbal). The instantaneous measurements are not always resolved over the full interrogation window, (depending on the seeding particle density), and therefore the recorded set of 2,500 images is reconstructed out of the first 20 modes of a proper orthogonal decomposition (POD) algorithm of the wake, and are implemented in the same fashion as those of the wake behind a similar model with controlled pitch-yaw rotation dynamics (Lambert et al, 2016a). These modes are derived from the instantaneous velocity vectors that are decomposed as: *…”

Cable Suspension and Balance System with Low Support Interference and Vibration for Effective Wind Tunnel Tests

“…The CDPR can also maintain appropriate stiffness levels. Recently, various studies have applied CDPRs an attitude control systems in wind tunnel tests [19][20][21][22][23][24][25][26][27]. The capabilities of a CDPR can be enhanced such that it can function as a load measuring balance by adding appropriate sensors to cables.…”