The primary objective of this research is to develop a high-bandwidth pressure sensor to provide benchmark, time-resolved, dynamic pressure data in high-temperature combustion environments. Specifically, these sensors will be designed to be embedded within a system and provide remote interrogation which will enable pressure to be measured in situ and on line under extreme conditions. Ultimately, this sensing technology will lead to better understanding and increased efficiency of complex power generation systems. In order to achieve this objective, research in sapphire laser micromachining and thermocompression bonding via spark plasma sintering technology will be conducted to enable fabrication of a fiber optic lever pressure sensor that uses a sapphire optical fiber for transduction of the pressure-induced diaphragm deflection. The proposed project will result in instrumentation-grade, high-temperature sensors that enable flush mounted measurements without sensor cooling. Furthermore, the use of optical techniques enables “passive” device operation, with electronics located remotely from the sensor. After fabrication and packaging, the pressure sensor will be rigorously characterized in acoustic plane wave tubes under both ambient and high-temperature conditions to determine its performance as a quantitative measurement device.
The goal of this research is to develop a MEMS-based Five-hole Probe(5HP) that is able to measure the localized velocity vector (both the velocity magnitude and direction) and the static and dynamic pressure, in steady and/or unsteady flow fields. Five optical pressure sensors located on the hemisphere tip of the 5HP provide all information that is needed to resolve the flow. This 5HP is expected to be able to provide high spatial resolution, high frequency response and is compatible with elevated temperature environments. A primary focus of this research is on the microfabrication and micromachining of a die that incorporates five optical transducers and its successive packaging process. The completed sensors will be tested in flow cells and wind tunnels at UF for the final calibration.
Experimental and numerical results over the past decade have conclusively demonstrated the effectiveness of turbulent drag reduction (up to 40%) through near-wall control schemes such as oscillating walls and traveling waves. However, these promising results have yet to lead to a suitable surface for practical application. We are developing a new near-wall turbulence control technique based on a recently developed nanowire surface, composed of vertically aligned Barium Titanate (BaTiO3) nanowires. Since BaTiO3 is a highly coupled piezoceramic, the surface can be manipulated by application of an electric field; and conversely the surface generates an electric potential in response to an applied mechanical load. We have hypothesized that actuation of the nanowire surface can produce cross-stream motion that will alter the structure of the boundary layer over the nanowire surface, resulting in modification of the wall shear stress. This hypothesis is based on recently improved understanding of the correlation between low-speed streak instability and the generation of drag-inducing streamwise vortices; suppressing these vortices at their onset by transverse motion controls within the viscous sublayer has proven extremely effective at stabilizing the low-speed streaks, leading to significant drag reduction.
Directed energy applications require accurate and efficient transmission of optical energy to an intended target. A three dimensional turret design consisting of a hemispherical top with a flat aperture has proven to provide a convenient method of pointing and tracking lasers from airborne platforms. However, the turret's three-dimensional blunt design leads to complex separation phenomena which, in turn, leads to distortion in an otherwise planar emerging laser beam. This research proposes to develop an adaptive feedback control system to control the flow field around the turret in order to improve aero-optic performance.
To develop a wireless shear-stress sensor array to provide three-dimensional, time-resolved, fluctuating skin friction data to aid turbulence model development.
Each sensor is effectively an LC tank made up of a variable-capacitance floating element and an integrated inductor. The sensing antenna is inductively coupled to the tank and can detect a change in the resonant frequency caused by a displacement of the floating element. An array is realized by designing each sensor to have it’s own unique resonant frequency. Then a single broad spectrum antenna can monitor the entire array.
The realization of such an array will enable fundamental scientific studies of complex turbulent flows. It could also be implemented into a feedback control system for future air vehicles employing active flow control.
This project focuses on the development of a non-intrusive, direct, time-resolved wall shear stress sensor system for low-speed applications. The goals of the project include the fabrication and packaging of a 2-D wall-shear stress sensor with backside wire bond contacts to ensure hydraulic smoothness in flow environments. A differential capacitance transduction scheme is utilized with interdigitated comb fingers on each side of a suspended floating element, allowing for measurements to be made in both the positive and negative x- and y-directions. A synchronous modulation-demodulation circuit is employed to simultaneously capture both mean and fluctuating shear content. Both AC and DC calibrations are performed to determine sensor sensitivity in both directions of transduction. This is the most successful effort of shear sensor development in published literature.
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.
A detailed study of the effect of blowing from a rounded wing tip on the attenuation of wing tip vortices generated by a NACA0012 semi-span airfoil is being conducted in two wind tunnels at IMG. The first, the UF Closed Circuit Wind Tunnel, will be used for measuring lift and drag of the airfoil and characterizing the wing tip flowfield using one or more flow measurement techniques such as particle image velocimetry, laser Doppler velocimetry and a fast-response Cobra probe. The second facility, the UF Aeroacoustic Flow Facility (UFAFF), is an open jet test section wind tunnel inside an anechoic chamber that will be primarily used to characterize the acoustics of the airfoil with far-field microphones and phased acoustic arrays. Lift and drag will also be measured in the UFAFF to determine the effect, if any, of the differing wind tunnel configurations on aerodynamic performance.
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 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.