Browsing by Author "Sullivan, Pierre E."

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Active Flow Control Using Synthetic Jet Actuation
(2011-01-05T20:34:18Z) Goodfellow, Sebastian ; Sullivan, Pierre E. ; Mechanical and Industrial Engineering
The influence of periodic excitation from synthetic jet actuators, SJA, on boundary layer separation and reattachment over a NACA 0025 airfoil at a low Reynolds number is studied. All experiments reported are performed in a low-turbulence recirculating wind tunnel at a Reynolds number of 100000 and angle of attack of α=5◦. Mounted below the surface of the airfoil, the SJA consists of four 32.8 mm diameter piezoelectric ceramic diaphragms positioned in a single row. Flow visualization results show a reattachment of the boundary layer and a significant reduction in wake structure. Velocity proﬁles downstream of the trailing edge and the results show a drastic reduction in wake size as excitation is introduced. A spectral analysis was conducted in the wake region and showed the presence of vortex shedding at a frequency of 22 Hz. When excitation was applied at 935 Hz and 250 Vp−p, the shedding frequency shifted to 50Hz.
Airfoil Performance at Low Reynolds Numbers in the Presence of Periodic Disturbances
(ASME, 2006-05) Yarusevych, Serhiy; Kawall, J. G.; Sullivan, Pierre E.
The boundary-layer separation and wake structure of a NACA 0025 airfoil and the effect of external excitations in presence of structural vibrations on airfoil performance were studied experimentally. Wind tunnel experiments were carried out for three Reynolds numbers and three angles of attack, involving hot-wire measurements and complementary surface flow visualization. The results establish that external acoustic excitation at a particular frequency and appropriate amplitude suppresses or reduces the separation region and decreases the airfoil wake, i.e., produces an increase of the lift and/or decrease of the drag. The acoustic excitation also alters characteristics of the vortical structures in the wake, decreasing the vortex length scale and coherency. Optimum excitation frequencies were found to correlate with the fundamental frequencies of the naturally amplified disturbances in the separated shear layer. The results suggest that acoustic waves play a dominant role in exciting the separated shear layer of the airfoil. Moreover, low-frequency structural vibrations are found to have a significant effect on airfoil performance, as they enhance the sound pressure levels within the test section.
An Enhanced Python-Based Open-Source Particle Image Velocimetry Software for Use with Central Processing Units
(2023-10-27) Shirinzad, Ali; Jaber, Khodr; Xu, Kecheng; Sullivan, Pierre E.
Particle Image Velocimetry (PIV) is a widely used experimental technique for measuring flow. In recent years, open-source PIV software has become more popular as it offers researchers and practitioners enhanced computational capabilities. Software development for graphical processing unit (GPU) architectures requires careful algorithm design and data structure selection for optimal performance. PIV software, optimized for central processing units (CPUs), offer an alternative to specialized GPU software. In the present work, an improved algorithm for the OpenPIV–Python software (Version 0.25.1, OpenPIV, Tel Aviv-Yafo, Israel) is presented and implemented under a traditional CPU framework. The Python language was selected due to its versatility and widespread adoption. The algorithm was also tested on a supercomputing cluster, a workstation, and Google Colaboratory during the development phase. Using a known velocity field, the algorithm precisely captured the time-average flow, momentary velocity fields, and vortices.
Analytical Models to Determine the Electric Field Characteristics of a Multi-Electrode Impedimetric Immunosensor in a Digital Microfluidic Device
(The American Society of Mechanical Engineers, 2015-03-13) Blume, Steffen O. P.; Schertzer, Michael J.; Ben Mrad, Ridha; Sullivan, Pierre E.
The level of integration of digital microfluidics is continually increasing to include the system path from fluid manipulation and transport, on to reagent preparation, and finally reaction detection. Digital microfluidics therefore has the capability to encompass all steps of common biochemical protocols. Reported here is a set of analytical models for the design of a coplanar interdigitated multi-electrode array to be used as an impedimetric immunosensor in a digital microfluidic device for on-chip chemical reaction detection. The models are based on conformal mapping techniques, and are compared to results obtained from finite element analysis to discuss limitations of the model. The analytical models are feasible and inexpensive surrogates for numerical simulation methods.
Apparatus for the Dynamic Calibration of Low-Range Differential Pressure Transducers
(American Institute of Aeronautics and Astronautics, 2017-12-22) Feero, Mark A.; Lavoie, Philippe; Sullivan, Pierre E.
Application of an Equilibrium Model for an Electrified Fluid Interface—Electrospray Using a PDMS Microfluidic Device
(Institute of Electrical and Electronics Engineers, 2008-11-11) Chiarot, Paul R.; Gubarenko, Sergey I.; Ben Mrad, Ridha; Sullivan, Pierre E.
An experimental investigation of an electrified fluid interface is presented. The experimental findings are related to a previously developed analytical model of Gubarenko , which is used to determine when a fluidic interface under electrical stress is in equilibrium, and to observations reported in the literature. The effect of key parameters on causing the interface to rupture, form, and maintain an electrospray is investigated. The experimental results reveal the dependence of interface shape on operational parameters, the impact of the interface apex angle on equilibrium, the conditions that cause either dripping mode or cone-jet mode, and the structure of operational domains. This paper confirms predictions made using the analytical model, including the range of parameters that cause the onset and steadiness of a quasi-equilibrium (electrospray) state of the interface. Testing is performed using an electrospray emitter chip fabricated from two layers of Polydimethylsiloxane and one layer of glass. The model and experimental results assist in design decisions for electrospray emitters. Applications of electrified interfaces (electrosprays) are found in mass spectrometry, microfluidics, material deposition, and colloidal thrusters for propulsion.
The Axial Spray Mode I as a Solution for Miniaturized Ion Mobility Spectrometry
(2014-03) Zahar, Khalil; Sullivan, Pierre E.; Mrad, Ridha Ben; Mechanical and Industrial Engineering
Miniaturized ion mobility spectrometers present several advantages as portable chemical detection tools. They are fast, simple and inexpensive. However, they still suffer from low resolving power and hard implementation of ion gates in micro scale designs. Even in examples where they are successfully combined, ion gates cause dispersion, compression, and depletion effects that result in ion packets than are wider than desired. This thesis describes an alternative gating method that is free of ion gates and that can be used in liquid phase ion mobility spectrometry (LPIMS), a technique where conventional ion gates are currently unsuitable. A parametric study shows that the method proposed has the potential to achieve resolving powers comparable to macro scale designs if successfully coupled to LPIMS. Observations relating the maximum meniscus height to current measurements are presented and are of particular interest to E-jet printing and similar techniques.
Bi–global Stability Analysis in Curvilinear Coordinates
(AIP Publishing, 2019-10-10) Wang, Jinchun; Ziadé, Paul; Huang, Guoping; Sullivan, Pierre E.
A method is developed to solve biglobal stability functions in curvilinear systems which avoids reshaping of the airfoil or remapping the disturbance flow fields. As well, the biglobal stability functions for calculation in a curvilinear system are derived. The instability features of the flow over a NACA (National Advisory Committee for Aeronautics) 0025 airfoil at two different angles of attack, corresponding to a flow with a separation bubble and a fully separated flow, are investigated at a chord-based Reynolds number of 100 000. The most unstable mode was found to be related to the wake instability, with a dimensionless frequency close to one. For the flow with a separation bubble, there is an instability plateau in the dimensionless frequency ranging from 2 to 5.5. After the plateau and for an increasing dimensionless frequency, the growth rate of the most unstable mode decreases. For a fully separated flow, the plateau is narrower than that for the flow with a separation bubble. After the plateau, with an increased dimensionless frequency, the growth rate of the most unstable mode decreases and then increases once again. The growth rate of the upstream shear layer instability was found to be larger than that of the downstream shear layer instability.
Bi-Global Stability Analysis on a NACA0025 Airfoil at a Reynolds Number of 100,000
(2019-07-30) Wang, Jinchun; Ziade, Paul; Huang, Guoping; Sullivan, Pierre E.
A method is developed to solve bi–global stability functions in curvilinear systems which avoids the reshaping of the air- foil or remapping the disturbance flow fields. As well, the bi–global stability functions for calculation in a curvilinear system are derived. The instability features of airfoil flow at AOA = 5 are studied and the most unstable mode was found to be related to the wake mode with a dimension- less frequency close to one, as found experimentally. As the span wise wave number increases, then number of unstable modes increases and then stabilizes. A graphical processing unit(GPU) is employed to speed up the solution of the eigenvalue problem. For large matrices, the calculation time using the GPU was roughly one–tenth the calculation time of a CPU.
A CFD study of the influence of turbulence on undercatch of precipitation gauges
(Elsevier, 2017) Baghapour, Behzad; Sullivan, Pierre E.
The response of precipitation to turbulent fluctuations near gauges is studied using time-averaged (RANS) and unsteady (LES) turbulence modeling. Updrafting effects on catch performance are analyzed for unshielded and shielded gauges. The effective precipitation catchment area of the gauge for both wind-induced effects and snowflake characteristics is found to reduce significantly for small particles in high winds but can be partly recovered by shielding. The variation in the amount of precipitation caught is quantified for different free-stream wind speeds using LES and RANS. The fluctuations, captured with LES are analyzed to determine the local structure of eddies near the orifice plane. Wind-induced drag on precipitates are modeled for a wide range of particle Reynolds numbers from low speed Stokes flow condition to high speed flows with inertial effects. Results show noticeable effect of drag–force model on catch performance calculation of precipitation gauges with uncertainties of up to 40% in high winds and large snowflake sizes. Finally, particle–wall collision on the catch performance is studied for different restitution conditions. These simulations have differences of up to 5% in catch performance for large particle sizes in high winds, dependent on whether the particles undergo elastic or plastic collisions. Comparing RANS and LES results, turbulence fluctuations show a considerable influence on shielding performance degeneration at high winds. Double shielding the gauge can improve efficiency by maintaining a lower fluctuation-to-mean catch ratio as wind speed increases.
Characterization of coplanar electrode structures for microfluidic-based impedance spectroscopy
(Elsevier, 2015-05) Blume, Steffen O. P.; Ben-Mrad, Ridha; Sullivan, Pierre E.
Impedance spectroscopy has the potential for label-free integrated electrochemical detection in microfluidic lab-on-a-chip applications. Its capability to identify and discern between surface and bulk processes in solid-liquid systems finds particular use for the detection of biorecognition events or conductivity measurements. The electrochemical transducer can be in the form of interdigitated electrode structures to increase sensitivity. Experimental work was performed to characterize two different transducer designs. Applications included the monitoring of protein films on contact-less interdigitated electrode structures and conductivity detection of droplets on insulated two-electrode structures. The use of electrode passivation eliminated electrode degradation. Experimental results were compared to theoretical analytical models, and were found to closely correlate with one another. The analytical models were used to design the transducer for optimal conductivity detection. The results inform the current research efforts for the development of in-line impedance spectroscopy in digital microfluidics and confirm the use of simple analytical models for the first-order estimation of the frequency response of interdigitated electrode structures.
Characterization of the Motion and Mixing of Droplets in Electrowetting on Dielectric Devices
(2011-02-23T21:02:32Z) Schertzer, Michael John ; Mrad, Ridha Ben ; Sullivan, Pierre E. ; Mechanical and Industrial Engineering
The physical mechanism responsible for droplet manipulation in electrowetting on dielectric (EWOD) devices is not yet fully understood. This investigation will examine the role of capillary forces on droplet manipulation to further the physical understanding of these devices. An analytical model for the capillary force acting on a confined droplet at equilibrium is developed here. Model predictions were validated using optical measurements of the droplet interface in the vertical plane. It was found that the capillary force and interface shape predicted by the equilibrium model were over an order of magnitude more accurate than predictions from the model commonly used in EWOD investigations. The equilibrium model was adapted to droplets with arbitrary shapes to predict droplet dynamics in EWOD devices. It was found that droplet motion could be described using the driving capillary force and frictional forces from wall shear, the contact line, and contact angle hysteresis. Comparison with experimental data shows that this model accurately predicts the effects of applied voltage and droplet aspect ratio on the transient position and velocity of droplets. This model can be used to design EWOD devices and predict the simultaneous manipulation of droplets required to meet the high throughput demands of practical applications. A robust system for droplet monitoring must be automated before EWOD devices can be used reliably in practical applications. Although capacitance measurements have been used to automate droplet detection in EWOD devices, manual optical measurements are generally used to monitor droplet mixing. This may not be possible in high throughput applications with multiple droplets and limited optical access. Here, capacitance measurements are shown to be an accurate and repeatable means of monitoring droplet composition and real time mixing. Experiments were performed with this technique to show that mixing efficiency is better characterized by the number of translations required for full mixing, not mixing time.
Comparison of Numerical and Experimental Results over a NACA0025 Airfoil Undergoing Separation
(MedCrave, 2018-02-12) Ahadi, Amirhossein; Sullivan, Pierre E.; Saghir, Ziad
This paper examines unsteady numerical simulation of a three-dimensional flow over two different symmetric NACA airfoils. The airfoils are at various angles of attack and various low Reynolds numbers ( ) 4 6 5 10 ~ 5 10 × × . The Spalart-Allmaras, and k − ε models, as well as LES and E-LES approaches are used and compared to experimental results. The capability of each turbulent model to capture characteristics at low Reynolds number is discussed. The main objective in this study is to capture the behavior of boundary-layer separation with respect to experiments at critical Reynolds numbers and then to establish a useful solution methodology describing transition in the boundary layer of airfoils accurately. Fully attached flow, boundary-layer separation, and boundary-layer with reattachment conditions are studied. Although LES and E-LES provide the highest computation cost, results show the accuracy of these methods at low Reynolds numbers (< 150 x103 ). For higher Reynolds number, turbulence models provide a fair agreement with experiments; while the processing cost of LES method is very high. Finally, the impact of airfoil thickness, Reynolds number, and angle of attack on the boundary-layer separation and consequently airfoil performance are studied in detail.
Design and Evaluation of an Improved Mixer for a Selective Catalytic Reduction System
(2014-03) Stelzer, David; Wallace, James; Sullivan, Pierre E.; Mechanical and Industrial Engineering
More stringent environmental regulations have created a requirement for Selective Catalytic Reduction (SCR) after-treatment technology on stationary Diesel engines. In this work, Computational Fluid Dynamics (CFD) is used in conjunction with a separate 1-D catalyst reaction model to evaluate the overall performance of the combined High Efficiency Vortab (HEV) mixer and U-bend design. This model yielded mixing results with a Uniformity Index (UI) of 97% while generating less than 10 ppm of NH3 slip. The compact nature of the combined design creates an SCR that is easy to install and manufacture. Pressure drop, was also determined to be less than 10” of water (WC) over the range of operating conditions. The performance from this design will assist engineers in meeting current and next generation environmental regulations.
Design of a Microfluidic Based Lab-on-a-chip for Integrated Sample Manipulation and Dispensing
(2012-06) Ahamed, Mohammed Jalal ; Mrad, Ridha Ben ; Sullivan, Pierre E. ; Mechanical and Industrial Engineering
Microfluidic based miniature lab-on-a-chip devices integrate different laboratory functionality in microscale. Microarray technology is evolving as a powerful tool for biomedical and pharmaceutical applications to identify gene sequences or to determine gene expression levels. Preparation of samples and spotting the arrays are the two major steps required for making microarrays. The microfluidic components developed in this research would facilitate performing the above-mentioned steps by a single lab-on-a-chip. Three microfluidic modules were developed: a non-contact microdispenser, an interface connecting the microdispenser with planar Electrowetting on Dielectric (EWOD) sample manipulator and a microvalve that controls the flow at the interface. An electrostatically actuated non-contact type drop-on-demand based microdispenser was developed. The dispenser was designed using finite element modeling technique that solved electrostatically actuated dispensing process. Prototypes were fabricated and tested verifying stable droplet dispensing with error in subsequent droplet generation was less than 15% between each droplet. The frequency of stable generation was 20 Hz and the average volume of dispensed droplet was 1 nL. A closed-channel EWOD actuated interface was developed that allowed a series of droplets to merge inside at the interface converting droplet flow to a continuous flow. An innovative design modification allowed series of droplet merging inside closed-channel. The interface allows integration of pressure driven devices such as: pumps, dispensers, and valves with droplet based planar EWOD devices. A novel EWOD based microvalve was developed that utilizes a thermo-responsive polymer to block and unblock a pressurized continuous flow. EWOD actuation was used to control the positioning of the valving polymer at location of interest. The valve also isolated a pressurized flow from an integrated planar EWOD device. Valves with zero leak rates were demonstrated. Such a valve will be useful in controlling microflows in EWOD to pressure driven flows such as dispensers.
Dynamic Mode Decomposition Analysis of Flow Separation in a Diffuser to Inform Flow Control Strategies
(American Society of Mechanical Engineers, 2020-02) Wang, Jinchun; Huang, Guoping; Lu, Weiyu; Sullivan, Pierre E.
In this work, a large eddy simulation of a typical subsonic diffuser provides data used to analyze coherent structure in a separated flow with dynamic mode decomposition (DMD). From this, a low–dimensional approximation, which retains the main dynamic characteristics of the original flow fields, is obtained. In particular, specific dynamic structures associated with a unique frequency are isolated. The spatial structure of the real and imaginary parts of the DMD mode are similar but with a phase difference. The contribution of the conjugate modes to the evolution of the DMD modes over time are discussed. The dominant frequency is found to be related to the wake mode. The scale of wake will saturate, and the shear layer will become weaker and merges into the wake structure as it develops downstream. This allows direction for effective flow control strategies using this information.
Effect of Acoustic Excitation Amplitude on Airfoil Boundary Layer and Wake Development
(2007-04) Yarusevych, Serhiy; Sullivan, Pierre E.; Kawall, John G.
The effect of acoustic excitation amplitude on boundary layer and wake development for a NACA 0025 airfoil was studied experimentally at low Reynolds numbers. Flow characteristics were investigated with hot-wire anemometry, surface pressure measurements, and flow visualization. A laminar boundary layer separation occurs on the upper surface of the airfoil, forming a separated shear layer, for all situations examined. When the flow is excited at the frequency matching the frequency of the most amplified disturbance in the separated shear layer, natural shear layer disturbances lock onto the excitation frequency and transition is promoted. In the case when the separated shear layer fails to reattach, an increase of the excitation amplitude above a minimum threshold eventually results in shear layer reattachment. The results suggest that an increase of the excitation amplitude not only advances the location of reattachment but also delays boundary layer separation, thereby reducing the extent of the separation region. As a consequence, excitation results in narrowing of the wake and diminishment of the length scales and coherence of the organized wake structures. However, this effect is eventually limited, and a maximum effective excitation amplitude can be identified. It is also shown that an increase of the excitation amplitude has a broadly similar effect on flow patterns to an increase of the chord Reynolds number.
Effect of varying frequency of a synthetic jet on flow separation over an airfoil
(AIP Publishing, 2022-01) Kim, M.; Essel, E. E.; Sullivan, Pierre E.
An experimental investigation on the effects of the synthetic jet actuator (SJA) was conducted on a NACA (National Advisory Committee for Aeronautics) 0025 airfoil in a low-speed recirculating wind tunnel at a chord Reynolds number of 100,000 and at an angle of attack 12°. Particle image velocimetry was used to visualize the flow separation for the uncontrolled baseline flow, and the flow attachment for the SJA controlled flows. The location of the SJA was at -1.3% from the separation point, and a blowing ratio of 0.8 was chosen for this study. The blowing ratio proved to be effective in suppressing the separation of the flow. The reduced frequency (𝑆𝑡𝑒) was varied between 1, 2, 14, and 58. The momentum bursts from the SJA based on the reduced frequency determined the effectiveness of the control method. The Reynolds stresses and turbulence production decreased dramatically with increasing frequency up to the shear layer frequency (𝑆𝑡𝑒= 14), but further excitation (𝑆𝑡𝑒= 58) resulted in a regain of turbulence levels. Proper orthogonal decomposition (POD) was performed which showed that the low frequency operations globally affect the modes in the shear layer while the high frequency operations are confined to the airfoil surface.
Emergent Inpatient Admissions and Delayed Hospital Discharges
(2010-11) Wong, Hannah Jane ; Sullivan, Pierre E. ; Mechanical and Industrial Engineering
Emergency Department (ED) congestion can be better understood by examining overall system impacts, in particular inpatient admissions and discharges. This study first investigates trends of inpatient admissions, volume of patients in the ED who have been admitted (ED “boarders”), length of stay, and bed resources of three major admitting services at our teaching institution. It was found that patients admitted to the General Internal Medicine (GIM) service constituted the majority of ED boarders by default rather than design, as GIM served as a safety net for specialty services. This study investigates operational factors that impact discharge and found that day of the week and holidays followed by team organization and scheduling are significant predictors of daily variation in discharge rates. Based on these results, next, a system dynamics computer simulation was built to test the impact of various discharge smoothing strategies on the number of ED boarders. Next, this study uses the framework and tools of system dynamics methodology to design a conceptual model of the ED boarder problem that may be used as a generalizable roadmap to create sustainable improvements in ED congestion. Finally, this study introduces a novel real time metric of hospital operational discharge efficiency- daily discharge rate – to bring focus on the underlying causes of discharge variation and help indicate opportunities for improvement.
An empirically validated model of the pressure within a droplet confined between plates at equilibrium for low Bond numbers
(Springer-Verlag, 2010-05) Schertzer, Michael; Gubarenko, Sergey; Ben-Mrad, Ridha; Sullivan, Pierre E.
An analytical model is presented that describes the equilibrium pressure within a confined droplet for small Bond numbers without prior knowledge of the interface shape. An explicit equation for the pressure was developed as a function of the gap height, surface tension, and contact angle. This equation was verified empirically. The shape of the interface was found based on the pressure predicted by both the proposed model and a model commonly used in electrowetting on dielectric (EWOD) investigations. These shapes were compared against experimentally observed interfaces for aspect ratios between 3.5 and 18. The pressures and shapes predicted by the proposed model were at least an order of magnitude more accurate than those predicted with a more commonly used model. At anaspect ratio of 3.5, the average error in the predicted shape was almost 4%, but decreased below the experimental error at an aspect ratio of 6. An aspect ratio of 15 is required for an EWOD device to split water droplets in air. The error in the model pressure and its predicted interface in this case were approximately 0.3%. The analytical pressure model proposed here can be used to increase the accuracy of models of practical EWOD devices. Better accuracy can be attained for small aspect ratios by iteratively calculating pressure using the model proposed here.