The goal of this research is to design and develop a new type of piezoelectric actuator based on dynamic surface modification in the form of low-aspect-ratio, dynamic, cylindrical pins. The major objectives are to implement an array of these dynamic, discrete elements onto a flapped airfoil model, scaled for realistic conditions, as a means of controlling the separation over the deflected control surface. This project encompasses both fundamental research as well as larger scale application.
The target for this research is to investigate how the dynamic surface modification actuators introduce vorticity and momentum as a means of energizing the boundary layer to delay or mitigate separation altogether. In order to optimize the actuators for specific flow conditions, we need to determine wich mechanisms contribute most to the modification of the flowfield. The flapped NACA0012 airfoild model is given in Figure 1 where flow is from left to right. The grey module in the center region, just upstream of the deflected rudder, contain 33 orifices divided into three spanwise-oriented rows along the chord. These orifices represent the locations of the low-aspect ratio dynamic pins and their streamwise and spanwise locations. Placing the array of actuators at various locations upstream of the separation point will allow for a thorough investigation of parameters wich will affect the extent of separation control, i.e., streamwise and spanwise location with respect to separation point, spacing between pins, aspect ratios, driving frequency, and amplitude.
With this goal in mind, the fundamental flow physics must first be understood in order to determine how a single low-aspect ratio pin impacts the flow field. Figure 2 represents a flate plate study, i.e., zero pressure gradient, whereby the interaction of a single dynamic pin with a laminar boundary layer was investigated using surface oil flow visualization techniques to qualitatively observe regions of attached and separated flow as well as Stereoscopic Particle Image Velocimetry (SPIV) to capture the resulting complex, three-dimensional flow patterns associated with a cylinder submerged within the boundary layer. To more thoroughly understand the flow behaviors associated with the dynamic motion of the pin, Figures 3 and 4 represent phase-averaged iso-surfaces of wall-normal velocity and Q-criterion, respectively. Figures 3a-d show four phases along the dynamic cycle which exhibit periodicity in the shedding of an arch-vortex coupled with the counter-rotating horseshoe vortex. Figures 4a-d represents the same four phases along the dynamic cycle colored by streamwise vorticity in areas where rotation is dominant. Thus, we are able to capture shedding vortical structures downstream of the dynamic pin.
Fundamental understanding of the flowfield being modified is crucial to determine the optimal design parameters of the actuator as well as the design of experiments. The results indicate the employing this method of active flow control can take advantage of naturally-occuring structures in the flow, augmenting their size and strength, as well as exciting specific modes of instability. This information is highly significant in the design and performance optimization of the flow control actuators as a means of separation control on larger scale application-based experiments.
Figure 2: (a) Surface oil flow visualization for a signle pin as flow comes from top to bottom, where the white circle indicates the erected pin, and black circles indicate pins which are flush to the test section floor, and (b) Time-Averaged iso-surface of wall-normal velocity taken from SPIV for a single dynamic pin, where red color indicates positive wall-normal velocity and blue color indicates negative wall-normal velocity.
Figure 3: 3-D iso-surfaces of phase-averaged normalized wall-normal velocity for the high actuation amplitude, high frequency dynamic case at phases of Ø = 0° (a), 90° (b), 180°(c), and 270° (d).
Figure 4: Iso-surfaces of the Q-criterion colored with positive (red) and negative (blue) streamwise vorticity for the high actuation amplitude, high frequency dynamic case at phases of Ø = 0° (a), 90° (b), 180°(c), and 270° (d).
- Gildersleeve, S., Tuna, B.A., and Amitay, M., "Interactions of a Low Aspect Ration Cantilevered Dynamic Pin with a Laminar Boundary Layer," AIAA Journal, http://dx.doi.org/10.2514/1.J055632, May 2017.
- Gildersleeve, S., and Amitay, M., "Control of Flow Separation over a Flapped Airfoil using Low Aspect Ratio Circular Pins," submitted to AIAA Journal, May 2017.
- Gildersleeve, S., and Amitay, M., "Dynamic Pin Actuator and its Application for Separation Controll," 57th Israel Annual Conference on Aerospace Sciences, Tel-Aviv & Haifa, Israel, March 15-16, 2017.
- Gildersleeve, S., Amitay, M., and Clingman, D., "Flow around Low Aspect Ration Cylinders and their Applications, " 55th AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, Grapevine, Texas, AIAA 2017-1449, January 2017.
- Gildersleeve, S., Clingman, D., and Amitay, M., "Separation Control over a Flapped NACA 0012 Model using an Array of Low Aspect Ratio Cylindrical Pins, " Aviation 2016, June 13-16, Washington DC, 2016.