Aerodynamic Flow Control of a Moving Axisymmetric Bluff Body

Abstract

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.

Aerodynamic Control of Coupled Body-Wake Interactions

“…In the present investigations, an axisymmetric bluff body integrated with individually-controlled miniature fluidic actuators is wire-mounted on a programmable 6-DOF (x/y/z-translation & pitch/yaw/roll) eight-wire traverse that is electromechanically driven by a dedicated feedback controller to remove the parasitic mass and inertia of the dynamic support system and of the model. The interactions between the The present investigations build on the earlier work of Lambert et al 29,30 who demonstrated that the aerodynamic loads induced by an azimuthal array of hybrid synthetic jet actuators on an axisymmetric bluff body are comparable to the corresponding aerodynamic loads that are generated during pitch motion over a broad range of frequencies in the absence of actuation, and in addition, the vortex shedding could be excited in this pitching direction. The goal of the current investigation is to demonstrate that this control approach is robust enough to control the wake in combined pitch and yaw.…”

“…The current investigation studies flow around a bluff body wind tunnel model (D = 90 mm, L = 165 mm) which is shown in Figures 1a and b (side and back, views). The model is scaled based on the earlier investigations of McMichael et al 14 and Abramson et al 16,17 , and is the same model used in Lambert et al 18,29,30 . The model is built using both stereo-lithographed and aluminum components.…”

“…The model motion is controlled through a trajectory tracking controller which was utilized in two previous studies by Lambert et al 29,30 and is shown in Figure 3. The two command inputs are a time trace for the desired model trajectory in 6-DOF, and a time trace for the actuation commands to modulate all four synthetic jet resonance waveforms (each at an inner frequency of f act ) for the desired induced jet effects.…”

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

“…Hybrid flow control was also demonstrated by Nagib et al (1985) who combined a short backward-facing step with a jet to control local separation. The earlier works of Lambert et al (2014Lambert et al ( , 2015aLambert et al ( , 2015b demonstrated that the aerodynamic loads induced by an azimuthal array of hybrid synthetic jet actuators (each utilizing a Coanda surface and a backward-facing step) on an axisymmetric bluff body are comparable to the corresponding flow-induced aerodynamic loads that are generated during pitch rotation over a broad range of frequencies in the absence of actuation. In addition, vortex shedding could be excited in pitch, and such actuation is implemented in the present work for trajectory control of the free moving 3-DOF body.…”

“…The model, which is scaled based on the earlier investigations of Lambert et al (2014Lambert et al ( , 2015aLambert et al ( , 2015b is comprised of a stereo-lithographed outer shell that is mounted on a central bearing around a stationary nose piece, as shown in Figure 1a. The model is balanced by a bronze counterweight that is placed in the inner part of the moving nose.…”