Mehmet N. Tomac

A Review of Fluidic Oscillator Development

This review provides a detailed discussion of the historical development of fluidic oscillators and their application to flow control. Fluidic oscillators were initially developed in the 1960’s for a variety of applications, and have seen resurgent interest for their suitability for modern flow control applications. The devices produce an oscillating jet of fluid over a wide fan angle and have no moving parts, making them an attractive actuator concept. This review aims to highlight the most important historical papers of relevance to modern fluidic oscillator development. The reviewed works will extend from the early 1960’s to the most recent investigations, with a focus on the fundamental operating mechanisms of fluidic oscillators. The authors present this review as a short synopsis of fluidic oscillators for flow control, while a more comprehensive review will be submitted for archival publication in the near future.

Frequency Studies and Scaling Effects of Jet Interaction in a Feedback-Free Fluidic Oscillator

The work presented in this paper focuses on understanding the effects of scaling on fluidic oscillator performance, with a particular emphasis on the relationship between flow rate and oscillation frequency. The jet interaction feedback-free type of fluidic oscillator used in this investigation is a strong candidate for a flow control actuator, as it has high bandwidth, no moving parts, and high momentum capability. The aim of this study is to understand the basic fluid dynamics of fluidic oscillators, as well as to provide an engineering database of information for future oscillator designs. Results presented in this paper detail the frequency response of the fluidic oscillator under various geometric and supply fluid conditions. Scaling studies were performed in order to establish the operating range of the device. Oscillators were built and tested with different fluids in gas and liquid phases over a range of magnitude in flow rate and frequency response. Frequency maps of the oscillator response indicate a flow field that is rich in high-frequency content, with up to the 7 th harmonic visible in the spectra. Three different flow regimes were observed with particle image velocimetry with a refractive index matched fluid. An interesting modehopping behavior was also observed which varied with the size of the oscillator, aspect ratio, and test fluid.

Jet Interactions in a Feedback-Free Fluidic Oscillator at Low Flow Rate

In this work, the internal fluid dynamics and frequency characteristics of feedback-free fluidic oscillators are investigated experimentally for low flow rates below 3.4 mL/s. The internal flow field of feedback-free fluidic oscillator was extracted using a refractive indexmatched Particle Image Velocimetry (PIV) technique with the help of a problem-specific sensor setup for simultaneous frequency measurements in refractive index matching fluid. The oscillation mechanism for the low flow rate region was revealed with PIV measurements. Flow topologies extracted with the measurements were found to exhibit various flow features and the details of the jets interactions and vortical balance that lead to oscillatory behavior were discussed.

Investigation of Vibration Phenomena Induced by Air Flow Over Side View Mirror

This work develops an understanding of the flow mechanisms that induce vibrations on automotive side view mirrors. The unsteady nature of the flow over side view mirrors causes unsteady aerodynamic load distributions and flow-induced vibrations on the mirror assembly. These vibrations generate blurred rear-view images and higher noise levels, affecting the mirror functionality and passenger comfort. Certain geometrical design features of side view mirrors can exacerbate the flow-induced vibration levels of the mirror assembly significantly. This work quantifies the impact of these design features on the vibration amplitude, develops a methodology for testing mirror vibrations in a small, low-speed wind tunnel using only the mirror of interest, and delves into the interactions between the bluff body mirror geometry and its wake. Two similar side view mirror designs were investigated in this work by using laser-based vibrometry, flow visualization, particle image velocimetry, hot film anemometry, and surface stress sensitive film techniques. The magnitude of the vibrations was found to depend on the level of excursion in the dynamic location of flow separation, particularly when characteristic flow frequencies couple with the mirror housing natural frequency.

Investigation of Side-View Mirror Flow-Induced Vibration Phenomena

The primary objective of this research is to develop an understanding of the flow mechanisms which induce side-view mirror vibrations. The unsteady nature of the flow over side-view mirrors causes unsteady aerodynamic load distributions and flow-induced vibrations on the mirror assembly. These vibrations generate blurred rear-view images and higher noise levels, affecting the safety and comfort of the passengers. Geometrical design features of side-view mirrors exacerbate the flow-induced vibration levels of the mirror assembly significantly. This work quantifies the impact of these design features on the vibration amplitude; develops a methodology for testing mirror vibrations in a small, low-speed wind tunnel using only the mirror of interest; and delves into the interactions between the bluff body mirror geometry and its wake. Two similar side-view mirror designs, a baseline design and a turn-signal design, were investigated. The baseline mirror has a sharp-edged corner near the trailing edge, while the turn-signal design has an edge with an increased radius of curvature for the tip profile. A laser-based vibration measurement technique was developed and used to quantify vibration levels. Flow visualization, Particle Image Velocimetry (PIV), Constant Temperature Anemometry (CTA), and Surface Stress Sensitive Film (S3 F) techniques were used to understand the separation characteristics over the mirrors since the time-dependent changes in separation location directly affect the unsteady loading on the mirror. The flow over the turn signal mirror with larger tip radius has larger excursions in the separation location, a wider wake, increased unsteadiness, and higher vibration levels. Results at the high Reynolds numbers for these test conditions indicate the absence of a discrete vortex shedding frequency. However, vortical structures in the wake are correlated with unsteady movement of the separation location.Copyright