Active flow control is the foundation of future innovative aerodynamic concepts for improved vehicle efficiency. However, the active flow control community generally lacks efficient, powerful actuators and, more importantly, corresponding validated design methodologies capable of demonstrating potential benefits at realistic vehicle flight Mach numbers and Reynolds numbers. This research brings together a multidisciplinary team with expertise in electromechanical transducers, lumped element modeling, CFD, and experimental fluid dynamics to model, design, fabricate, and test advanced ZNMF actuators that use different transduction schemes: including piezoelectric and electrodynamic. The outcome of this research is a validated constrained design optimization tool that enables a class of robust ZNMF actuators for deployment on a larger scale.
Separated flow past an airfoil is characterized by multiple natural frequencies associated with various instabilities.
- Traditional separation control forces at a single frequency and often neglects the influence of actuator dynamics (resonance).
Questions & Objectives
- Is the effectiveness of a control strategy related to the natural flow instabilities and/or interactions?
Objective 1: Identify and analyze the various global dynamics in a separated flow configuration
- Can we detect and leverage natural instabilities to understand, model, and control separated flow in a more efficient and systematic manner?
Objective 2: Investigate the effectiveness and efficiency of targeting the instabilities in open-loop experiments
Objective 3: Apply observations to design and implement effective closed-loop control strategies
Challenges & Approach
1. Traditional experimental methods for detection of flow frequency content are limited
- Localized dynamic sensors (location sensitive)
- High-rate global measurements ($$$)
Approach: Use modal analysis methods amenable to experimental techniques to obtain low-order, global estimates
2. Characteristics of 2D flow separation on airfoils is highly dependent on angle of attack and surface curvature
Approach: A canonical flat plate model retains the essential separation characteristics, eliminates curvature effects, and is amenable to both simulations and experiments
1. Estimate global flow dynamics (time-resolved velocity fields)
2. Identify characteristic frequencies/instabilities
3. Perform open-loop control
Target characteristic frequencies by modulating actuator resonance. The extent and height of the time-averaged separation bubble is reduced during control.
Forcing at or near the natural shear layer frequency "feeds" the characteristic roll-up of the shear layer, which increases mixing between the high-momentum freestream and the low-momentum separated flow. This ultimately reattaches the flow further upstream with little control effort, or cost, described by the coefficient of momentum Cμ.
DMD extracts modal structures of the characteristic shear layer and wake components and results reveal interaction between the wake and separation bubble dynamics
Most efficient OL control scheme targets multiple flow instabilities rather than a single instability
- CL control reattaches the flow (time average) by reducing the controlled shear layer oscillations
The WEAV is a vehicle which is propelled by a plasma (ionized gas) discharge, requires no moving parts and provides near-instantaneous response. The vehicle operates in atmospheric pressure and is capable of 360° maneuverability. The key to the success of the project is to reduce the ratio of power to vehicle weight while significantly increasing the thrust generation capabilities of the plasma discharge.
The objective of the effort is to transition high-performance micromagnets into fully-integrated, batch-fabricated micromagnetic actuators for applications such as micro adaptive flow control.
Magnetically-based electromechanical actuation schemes are ubiquitous in macroscale systems such as audio speakers, relays, solenoids, and electrical motors. However, implementation of these transduction schemes at the microscale is nearly nonexistent because of certain design and fabrication challenges—primarily the inability to integrate high-performance, permanent-magnet (magnetically-hard) films within more complex micromachined structures. As a result, most microfabricated transducers rely on other transduction mechanisms (e.g. electrostatic, piezoelectric, thermoelastic). However, these mechanisms limit the actuation force, stroke (displacement), power density, and efficiency necessary for certain applications.
The proposed actuator uses an adaptable and scalable actuation scheme, in that the device structure can be tailored for a wide range of applications. Examples include micro pumps/valves for microfluidic (gas or liquid) systems; high power density motors/actuators for microrobotics; or low-profile acoustic radiators for navigations/sensing. The evolution of fully-integrated micromagnetic transducers will enable performance improvements for existing applications and opportunities to explore new transformative technologies.
(1) to validate and characterize the integrability (chemical stability, temperature stability, mechanical reliability, magnetization methods etc.) of the permanent magnet materials in complex microfabrication process flows
(2) to model and optimize a multi-magnet out-of-plane microactuation scheme
(3) to fabricate and characterize a fully-integrated out-of-plane piston-type actuator that can be directly implemented as a micro aerodynamic control surface or adapted as a synthetic jet actuator
Figure 1: CAD drawings of the proposed micro-electrodynamic synthetic jet actuator actuator: (a) Actuator assembly comprising two dies made from silicon substrate, separated by a separator. The top die is covered with a PDMS diaphragm and has a bonded powder magnet in the center. (b) Exploded view of the bottom wafer.