Institute for Integrated Energy Systems (IESVic)

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The Institute for Integrated Energy Systems at the University of Victoria (IESVic) promotes feasible paths to sustainable energy systems by developing new technologies and perspectives to overcome barriers to the widespread adoption of sustainable energy. Founded in 1989, IESVic conducts original research to develop key technologies for sustainable energy systems and actively promotes the development of sensible, clean energy alternatives.

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IESVic's mission is to chart feasible paths to sustainable energy.

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Now showing 1 - 9 of 9

Effect of chordwise flexibility and depth of submergence on an oscillating plate underwater propulsion system
(2010-11-15T17:54:13Z) Barannyk, Oleksandr; Buckham, Bradley Jason; Oshkai, Peter
The first part of this work was dedicated to the experimental study of basic principles of oscillating plate propulsors undergoing a combination of heave translation and pitch rotation. The oscillation kinematics are inspired by swimming mechanisms employed by fish and some other marine animals. The primary attention was the propulsive characteristics of such oscillating plates, which was studied by means of direct force measurements in the thrust-producing regime. Experiments were performed at constant Reynolds number and heave amplitude. By varying the Strouhal number, experimental depth and chordwise exibility of the plate it was possible to investigate corresponding changes in thrust and hydromechanical efficiency. After numerous measurements it was possible to establish an optimal set of parameters, including the system's driving frequency, the ratio of rigid to flexible segment length of the plate and the range of Strouhal number, that led to a peak efficiency near 80%. The experiments for different values of chordwise flexibility showed that greater flexibility increases the propulsive effciency and thrust compared with similar motion of the purely rigid foil. By submerging the plate at different depths, it was observed that the proximity of the propulsor to the channel floor led to overall increase in the thrust coefficient. However the increase in thrust coefficient was pronounced in the range from middepth to the floor of the water tunnel. The special case when the upper plate's edge is tangential to the undisturbed free surface is discussed separately. The second part of this work introduces a semianalytic approach for calculating the influence of piezoelectric (PZT) actuators on the free vibration characteristics of an Euler-Bernoulli clamped free beam. The beam represents a simplifled version of the fish tail whose stiffness is proposed to be controlled by placing a pair of PZT actuators in strategic regions along the caudal area of the tail. This approach, according to earlier studies, improves efficiency if tail natural frequency matches tailbeat frequency. The approach used an existing form of a transfer matrix technique developed for the analysis of non-proportionally damped slender beams. The PZT dynamics were incorporated into this recursive procedure through a modification that accounted for the tendency of the PZT patches to couple the dynamics of the node points of the segmented Euler-Bernoulli beam. To ensure stability of the system, an angular ve- locity feedback law, originally motivated by vibration suppression applications, was chosen for the PZT actuators. The sensitivities of the tail modes of vibration to the location of the PZT elements and the control gain were determined. Mode shapes for the revised modes were determined and it was shown that the first, second and the third modes maintained similar norms as tail shapes observed in anguilliform, sub- carangiform, and thunniform regimes of swimming. Using a semianalytic approach, it was shown that PZT location heavily in uences the frequency distribution of the modes of vibration. The control gain, when chosen within the limit of saturation voltage, is shown to be an effective control lever for vibration suppression and at rising the tail stiffness during rapid acceleration when the fish accelerates. However, the single PZT patch does not provide significant frequency adjustments such that different swimming modes could be employed efficiently with a single mechanical tail system primary actuator. To pursue such versatility for the sh tail, the tail structure must be very flexible to accommodate the significant frequency increase caused by the addition of the PZT material. Also, the use of additional PZT patches and negative control gains must be considered in order to use the PZT's to drop the higher modes (second and third) down into the frequency range of the primary actuation system, presuming the tail and primary actuator are designed for a thunniform regime of swimming.
Escort tug performance prediction: a CFD method
(2012-12-20) Smoker, Brendan; Oshkai, Peter
As the demand for energy continues to increase around the world, more vessels used in the transport of energy, such as Liquid Natural Gas (LNG) and crude oil tankers are being built to transport energy to market overseas. The escort tug has been developed in order to assist in the safe transit of such vessels in confined waterways. Designed to apply emergency braking and steering forces to the stern of a tanker while underway, an escort tug features a hull shape that generates large hydrodynamic lift and drag forces when operating at high angles of attack, this is known as indirect mode. This escorting mode is highly effective at speeds 8 knots and above, often generating towline forces well in excess of bollard pull. Escort performance prediction is a vital aspect of the design of escort tugs. It is important to know a priori if a design will meet the necessary performance criteria. In the past, performance predictions have relied heavily on model testing and empirical methods. With the recent emergence of Computational Fluid Dynamics (CFD) as a commercially viable design tool for naval architects, extensive escort performance predictions can now be carried out more accurately in less time and at less cost than was previously possible. This thesis describes the methodology of a CFD based escort performance prediction method that is accurate and cost effective.
Experimental investigation of the performance of a diffuser-augmented vertical axis wind turbine
(2011-10-18) Akhgari, Arash; Oshkai, Peter
The performance of a vertical axis wind turbine with and without a diffuser was studied using direct force measurement technique applied to a scaled model of the rotor in a water tunnel. The experiment was conducted at different tip-speed ratios. The maximum power coefficient for the turbine was found to be equal to 0.35 for the rotor with diffuser and to 0.26 for the rotor without diffuser. Therefore, the maximum power coefficient was increased by 35% when the diffuser was used in the configuration. In the second part of this work, the flow patterns downstream of the turbine were studied by the particle image velocimetry (PIV) technique. Six different tip-speed ratios were considered for each configuration (with and without a diffuser). The vorticity and the streamline plots provide insight into the flow physics in each configuration. In addition, the swept area of a full-scale rotor was calculated for both a diffuser-augmented and a bare turbine for a range of power outputs.
Experimental study of water droplet flows in a model PEM fuel cell gas microchannel
(2008-01-17T23:38:01Z) Minor, Grant; Djilali, Ned; Oshkai, Peter
Liquid water formation and flooding in PEM fuel cell gas distribution channels can significantly degrade fuel cell performance by causing substantial pressure drop in the channels and by inhibiting the transport of reactants to the reaction sites at the catalyst layer. A better understanding of the mechanisms of discrete water droplet transport by air flow in such small channels may be developed through the application of quantitative flow visualization techniques. This improved knowledge could contribute to improved gas channel design and higher fuel cell efficiencies. An experimental investigation was undertaken to gain better understanding of the relationships between air velocity in the channel, secondary rotational flows inside a droplet, droplet deformation, and threshold shear, drag, and pressure forces required for droplet removal. Micro-digital-particle-image-velocimetry (micro-DPIV) techniques were used to provide quantitative visualizations of the flow inside the liquid phase for the case of air flow around a droplet adhered to the wall of a 1 mm x 3 mm rectangular gas channel model. The sidewall against which the droplet was adhered was composed of PTFE treated carbon paper to simulate the porous GDL surface of a fuel cell gas channel. Visualization of droplet shape, internal flow patterns and Velocity measurements at the central cross-sectional plane of symmetry in the droplet were obtained for different air flow rates. A variety of rotational secondary flow patterns within the droplet were observed. The nature of these flows depended primarily on the air flow rate. The peak velocities of these secondary flow fields were observed to be around two orders of magnitude below the calculated channel-averaged driving air velocities. The resulting flow fields show in particular that the velocity at the air-droplet interface is finite. The experimental data collected from this study may be used for validation of numerical simulations of such droplet flows. Further study of such flow scenarios using the techniques developed in this experiment, including the general optical distortion correction algorithm developed as part of this work, may provide insight into an improved force balance model for a droplet exposed to an air flow in a gas channel.
Flow-induced sound and vibration due to the separated shear layer in backward-facing step and cavity configurations
(2009-11-25T22:05:33Z) Velikorodny, Alexey S.; Oshkai, Peter
Fully turbulent inflow past symmetrically located side branches mounted in a duct can give rise to pronounced flow oscillations due to coupling between separated shear layers and standing acoustic waves. Experimental investigation of acoustically-coupled flows was conducted using digital particle image velocimetry (DPIV) in conjunction with unsteady pressure measurements. Global instantaneous, phase- and time-averaged flow images, as well as turbulence statistics, were evaluated to provide insight into the flow physics during flow tone generation. Onset of the locked-on resonant states was characterized in terms of the acoustic pressure amplitude, frequency and the quality factor of the resonant pressure peak. Structure of the acoustic noise source is characterized in terms of patterns of generated acoustic power. In contrast to earlier work, the present study represents the first application of vortex sound theory in conjunction with global quantitative flow imaging and numerical simulation of the 2D acoustic field. In addition to the basic side branch configuration, the effects of bluff rectangular splitter plates located along the centerline of the main duct was investigated. The first mode of the shear layer oscillation was inhibited by the presence of plates, which resulted in substantial reduction of the amplitude of acoustic pulsations and the strength of the acoustic source. These results can lead to the development of improved control strategies for coaxial side branch resonators. Motivation for the second part of this study stems from the paper manufacturing industry, where air clamp devices utilize high-speed jets to position paper sheets with respect to other equipment. Thus, vibration of the paper sheet and turbulent flow that emerged from a planar curved nozzle between a flexible wall and a solid surface containing a backward-facing step (BFS) were investigated using high-speed photography and DPIV, respectively. The emphasis was on the characterization of the flow physics in the air clamp device, as well as of the shape of the paper sheet. For the control case, that involved a solid wall with a geometry that represented the time-averaged paper profile, hydrodynamic oscillation frequencies were characterized using unsteady pressure measurements. Experimentally obtained frequencies of the paper sheet vibration were compared to the hydrodynamic frequencies corresponding to the oscillations of the shear layer downstream of the BFS.
Investigation of a U-shaped fuel cell flow channel with particle image velocimetry (PIV)
(2008-04-10T06:00:36Z) Martin, Jonathan Jackie.; Djilali, Nedjib; Oshkai, Peter
Flow through an experimental model of a U-shaped flow channel is used to investigate the hydrodynamic phenomena that occur within serpentine reactant transport channels of fuel cells. Achieving effective mixing within these channels is crucial for the proper operation of the fuel cell and proper understanding and characterization of the underlying fluid dynamics is required. Particle image velocimetry (PIV) is used to investigate the three-dimensional structure of the flow by analyzing the velocity and associated vorticity field over two perpendicular channel cross-sections. A range of Reynolds numbers, 109 I Re I 872, corresponding to flow rates encountered in a fuel cell operating at low to medium current densities is investigated. The effect of the flow rate is characterized in terms of the instantaneous and time-averaged representations of the velocity vectors, out-of-plane vorticity and the velocity streamlines. At the lowest Reynolds numbers, the flow is steady and is characterized by high vorticity regions associated with shear layers separating from the sharp convex comers of the U-bend and reattaching on downstream surfaces. The flow also exhibits the classical secondary Dean flow pattern with two symmetric circulation zones. Transition takes place in the range 381 I Re I 436 as the two recirculation zones, which originally develop in the U-bend region, merge into one separation region. This transition is accompanied by the generation of additional vortices in the secondary flow plane. The relationship between the flow in both planes and the transition is examined along with properties of the instability including RMS, Reynolds stress, and the oscillation frequency. The quantitative flow visualization results obtained presented here should be useful in guiding numerical models of fuel cells, and indicate that the commonly used assumption of steady laminar flow should be revisited, and alternative models developed.
Quantitative imaging of multi-component turbulent jets
(2012-04-26) Ash, Arash; Djilali, Nedjib; Oshkai, Peter
The Gaseous state of hydrogen at ambient temperature, combined with the fact that hydrogen is highly flammable, results in the requirement of more robust, high pressure storage systems that can meet modern safety standards. To develop these new safety standards and to properly predict the phenomena of hydrogen dispersion, a better understanding of the resulting flow structures and flammable regions from controlled and uncontrolled releases of hydrogen gas must be achieved. In this study the subsonic release of hydrogen was emulated using helium as a substitute working fluid. A sharp-edged orifice round turbulent jet is used to emulate releases in which leak geometry is circular. Effects of buoyancy, crossflow and adjacent surfaces were studied over a wide range of Froude numbers. The velocity fields of turbulent jets were characterized using particle image velocimetry (PIV). The mean and fluctuation velocity components were well quantified to show the effect of buoyancy due to the density difference between helium and the surrounding air. In the range of Froude numbers investigated, increasing effects of buoyancy were seen to be proportional to the reduction of the Fr number. The obtained results will serve as control reference values for further concentration measurement study and for computational fluid dynamics (CFD) validation.
Shear layer instabilities and flow-acoustic coupling in valves: application to power plant components and cardiovascular devices
(2014-05-07) Barannyk, Oleksandr; Oshkai, Peter
In the first part of this dissertation, the phenomenon of self-sustained pressure os-cillations due to the flow past a circular, axisymmetric cavity, associated with inline gate valves, was investigated. In many engineering applications, such as flows through open gate valves, there exists potential for coupling between the vortex shedding from the up-stream edge of the cavity and a diametral mode of the acoustic pressure fluctuations. The effects of the internal pipe geometry immediately upstream and downstream of the shal-low cavity on the characteristics of partially trapped diametral acoustic modes were in-vestigated numerically and experimentally on a scaled model of a gate valve mounted in a pipeline that contained convergence-divergence sections in the vicinity of the valve. The resonant response of the system corresponded to the second acoustic diametral mode of the cavity. Excitation of the dominant acoustic mode was accompanied by pressure oscillations, and, in addition to that, as the angle of the converging-diverging section of the main pipeline in the vicinity of the cavity increased, the trapped behavior of the acoustic diametral modes diminished, and additional antinodes of the acoustic pressure wave were observed in the main pipeline. In addition to that, the effect of shallow chamfers, introduced at the upstream and/or downstream cavity edges, was investigated in the experimental system that con-tained a deep, circular, axisymmetric cavity. Through the measurements of unsteady pressure and associated acoustic mode shapes, which were calculated numerically for several representative cases of the internal cavity geometry, it was possible to identify the configuration that corresponded to the most efficient noise suppression. This arrangement also allowed calculation of the azimuthal orientation of the acoustic modes, which were classified as stationary, partially spinning or spinning. Introduction of shallow chamfers at the upstream and the downstream edges of the cavity resulted in changes of azimuthal orientation and spinning behaviour of the acoustic modes. In addition, introduction of splitter plates in the cavity led to pronounced change in the spatial orientation and the spinning behaviour of the acoustic modes. The short splitter plates changed the behaviour of the dominant acoustic modes from partially spinning to stationary, while the long split-ter plates enforced the stationary behaviour across all resonant acoustic modes. Finally, the evolution of fully turbulent, acoustically coupled shear layers that form across deep, axisymmetric cavities and the effects of geometric modifications of the cavity edges on the separated flow structure were investigated using digital particle image velocimetry (PIV). Instantaneous, time- and phase-averaged patterns of vorticity pro-vided insight into the flow physics during flow tone generation and noise suppression by the geometric modifications. In particular, the first mode of the shear layer oscillations was significantly affected by shallow chamfers located at the upstream and, to a lesser degree, the downstream edges of the cavity. In the second part of the dissertation, the performance of aortic heart valve pros-thesis was assessed in geometries of the aortic root associated with certain types of valve diseases, such as aortic valve stenosis and aortic valve insufficiency. The control case that corresponds to the aortic root of a patient without valve disease was used as a reference. By varying the aortic root geometry, it was possible to investigate corresponding changes in the levels of Reynolds shear stress and establish the possibility of platelet activation and, as a result of that, the formation of blood clots.
Tuning the passive structural response of an oscillating-foil propulsion mechanism for improved thrust generation and efficiency
(2013-11-19) Richards, Andrew James; Oshkai, Peter
While most propulsion systems which drive aquatic and aerial vehicles today are based on rotating blades or foils, there has recently been renewed interest in the use of oscillating foils for this purpose, similar to the fins or wings of biological swimmers and flyers. These propulsion systems offer the potential to achieve a much higher degree of manoeuvrability than what is possible with current man-made propulsion systems. There has been extensive research both on the theoretical aspects of oscillating-foil propulsion and the implementation of oscillating foils in practical vehicles, but the current understanding of the physics of oscillating foils is incomplete. In particular, questions remain about the selection of the appropriate structural properties for the use of flexible oscillating foils which, under suitable conditions, have been demonstrated to achieve better propulsive performance than rigid foils. This thesis investigates the effect of the foil inertia, stiffness, resonant frequency and oscillation kinematics on the thrust generation and efficiency of a flexible oscillating-foil propulsion system. The study is based on experimental measurements made by recording the applied forces while driving foil models submerged in a water tunnel in an oscillating motion using servo-motors. The design of the models allowed for the construction of foils with various levels of stiffness and inertia. High-speed photography was also used to observe the dynamic deformation of the flexible foils. The results show that the frequency ratio, or ratio of oscillation frequency to resonant frequency, is one of the main parameters which determines the propulsive efficiency since the phase of the deformation and overall amplitude of the motion of the bending foil depend on this ratio. When comparing foils of equivalent resonant frequency, heavier and stiffer foils were found to achieve greater thrust production than lighter and more flexible foils but the efficiency of each design was comparable. Through the development of a semi-empirical model of the foil structure, it was shown that the heavier foils have a lower damping ratio which allows for greater amplification of the input motion by the foil deformation. It is expected that the greater motion amplitude in turn leads to the improved propulsive performance. Changing the Reynolds number of the flow over the foils was found to have little effect on the relation between structural properties and propulsive performance. Conversely, increasing the amplitude of the driven oscillating motion was found to reduce the differences in performance between the various structural designs and also caused the peak efficiency to be achieved at lower frequency ratios. The semi-empirical model predicted a corresponding shift in the frequency ratio which results in the maximum amplification of the input motion and also predicted more rapid development of a phase lag between the deformation and the actuating motion at low frequency ratios. The shift in the location of the peak efficiency was attributed to these changes in the structural dynamics. When considering the form of the oscillating motion, foils driven in combined active rotation and translation motions were found to achieve greater efficiency but lower thrust production than foils which were driven in translation only. The peak efficiencies achieved by the different structural designs relative to each other also changed considerably when comparing the results of the combined motion trials to the translation-only cases. To complete the discussion of the results, the implications of all of these findings for the design of practical propulsion systems are examined.

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