Browsing by Author "Morton, Chris R."
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Item Open Access Added Mass and Vortical Impulse: Theory and Experiment(2019-01-10) Limacher, Eric John; Wood, David H.; Morton, Chris R.; Johansen, Craig T.; Martinuzzi, Robert John; Bates, Larry M.; Smits, LexThe classical decomposition of aerodynamic force into added-mass and circulatory components is derived under the assumption of inviscid flow. In the present thesis, this decomposition is shown to be valid for viscous flows. The classical added-mass force, derived using (acyclic) potential flow theory, is superimposable onto the circulatory force regardless of the presence of a vortical wake. This generalized added-mass and circulatory (GAMC) force decomposition is derived from impulse theory using a Helmholtz decomposition of the velocity field, and is valid for rigid bodies of any shape in unbounded incompressible fluid domains. Two supporting theoretical contributions were made in the course of the derivation, and these have been referred to as the conservation of image-vorticity impulse and the invariance of total vortical impulse to infinity-preserving conformal transformations. The practical utility of the GAMC formulation was investigated by applying it to a numerical simulation (generated by Wang and Eldredge (2013)) of the flow around a pitching plate in a steady free-stream flow. The calculated forces show fairly good agreement with the reported forces, although minor discrepancies suggest further work to quantify errors due to discretization. The GAMC formulation was then applied to particle image velocimetry (PIV) data to estimate force on a linearly accelerating cylinder in quiescent fluid. The resulting estimates capture the trend of the measured force well, but consistent underestimation of 10% to 20% was observed. It is speculated that the underestimation could be a failure to resolve the viscous skin friction due to spatial resolution limitations, and this possibility merits further study. In both the numerical and experimental validations, the GAMC formulation was validated alongside a common expression referred to as the standard impulse formulation (SIF). The inclusion of an image-vorticity impulse term in the GAMC formulation, contrary to the SIF, causes it to be less sensitive to random errors in the acquired velocity field and more tolerant to the omission of near-body vorticity data. These features of the GAMC formulation make it an attractive option for application to PIV studies in which near-body data acquisition is challenging.Item Open Access CFD simulation of Smooth and Rough NACA 0012 Airfoils at low Reynolds number(2018-12-11) Li, Yunjian; Wood, David H.; Morton, Chris R.; Johansen, Craig T.; Natale, GiovanniantonioThe objective of this study is to investigate the accuracy of turbulence model prediction in the computational fluid dynamics (CFD) of airfoil aerodynamic performance with and without roughness. It is very important to study the roughness effect on airfoil aerodynamic characteristics for wind turbine blades and aviation. Since roughness alters the lift and drag coefficients, it affects the aerodynamics performance directly. NACA0012 airfoil is used in the CFD simulation. Low Reynolds number of 1.5105 is used to allow comparison to experimental results, and high Reynolds number of 1.5106 is used to check the aerodynamic performance at conditions more suitable to large wind turbines, but for which there is no experimental data. The range of angle of attack (degrees) is from 0˚ - 10˚ as this covers the range that gives maximum power extraction. The roughness is selected from a previous experiment which is a sand grain roughness grit-36 with a 500μm thickness. The equivalent sand roughness height is used in turbulence models for rough surface simulation. This parameter represents the whole effect of the roughness. The simulation results of lift, drag, pressure and skin friction coefficients as well as the lift to drag ratio between smooth and rough surfaces are compared with the available experimental results. Three turbulence models: low Reynolds SST k-ω, transition-SST and SA models were used for the prediction. The results show the surface roughness can decrease the lift coefficient, lift to drag ratio and increase the skin friction and drag coefficients. At the low Reynolds number (1.5105), the prediction of low Reynolds SST k-ω, transition-SST on the smooth surface show a good agreement with the experimental data than SA model. However, only the low Reynolds SST k-ω model has a good consistency with the experimental results on the rough surface. At high Reynolds number (1.5106), the results of transition-SST on drag coefficients are more closed to experimental data than low Reynolds SST k-ω and SA model. Three models have similar results with experimental data on lift coefficients.Item Open Access Conceptual Design Framework for Transitional VTOL Aircraft with Application to Highly-Maneuverable UAVs(2019-08-30) Abdelrahman, Ashraf Mohamed Kamal Mahmoud; Ramírez-Serrano, Alejandro; Johansen, Craig T.; Morton, Chris R.; Shahbazi, Mozhdeh M.; Laliberté, Jeremy F.Transitional Vertical Take-off and Landing Aircraft (TVA) are systems capable of flying as Fixed-Wing (FW) aircraft and rotorcraft as well as transition between these flight modes. Responding to the technology advancement and impetus by the emerged mission needs, TVA have recently gained much interest in the aviation industry and many current/future aircraft are required/envisioned to have both the FW and rotorcraft capabilities in diverse potential applications. However, consolidating the characteristics of FW aircraft and rotorcraft increases the challenges when designing aircraft for which solutions currently do not exist. The number of Design Requirements (DRs) needed to be achieved and the number of contradictory Design Parameters (DPs) involved in the design process, further complicates the design process of TVA compared with traditional design methods for either FW aircraft or rotorcraft. Despite the maturity in the field of design for conventional FW aircraft and rotorcraft, considerable design work, techniques, and methodologies need to be specifically developed to tackle the challenges that exist in TVA design. Generally, the earlier design steps are the most important within any aircraft design and development process as significant decisions/calculations about the aircraft configuration are made with a somewhat limited knowledge about the aircraft. This thesis discusses the challenges/difficulties associated with the early design steps of TVA and introduces a newly developed conceptual design framework to tackle them. First, a systematic concept development methodology is developed with all necessary mathematical formulations and complementary benchmarks that integrates well-known methods/tools in a novel way suitable for TVA concept development. The proposed approach allows managing multiple conflicting criteria and coupled decisions. Furthermore, the methodology enables efficient exploration of a very large design space with different alternatives and complex design hierarchies to generate the most relevant aircraft configurations responding to a set of DRs and selecting the one that best meets the requirements. The proposed approach allows designers to examine more alternatives than what is feasible with traditional design methods and prevents designers from either choosing poor concepts due to the lack of experience or overlooking valuable ones. Second, a generalized formal sizing methodology for TVA is developed by modifying several assumptions typically made when using the available and well-known FW and rotorcraft performance equations. From such an approach, a new set of equations is developed to enable the simultaneous calculation of the adequate sizing parameters such that TVA satisfy the DRs in all of the three flight modes (i.e., FW, transition, and rotorcraft). In order to demonstrate and validate the capabilities and adaptation of the developed framework, the approach is applied to the conceptual design of an advanced unmanned highly-maneuverable TVA having challenging DRs (e.g., requirement to perform maneuvers not possible by traditional aircraft like pitch-hover and transition to FW flight mode at any attitude). The obtained results revealed that the proposed framework can be applied to TVA conceptual design with a reasonable level of confidence in its accuracy. The formulations and tools developed reduce the time typically needed to develop aircraft concepts and increase the chances to generate a final aircraft with high performance meeting the initial DRs.Item Open Access Experimental Investigation of Vortex-Induced Vibrations using a Cyber-Physical System(2018-09-11) Riches, Graham Paul; Morton, Chris R.; Bauwens, Luc; Zhou, Qi; Wood, David H.The dynamic response and wake of a circular cylinder undergoing vortex-induced vibrations (VIV) is investigated experimentally using a cyber-physical force-feedback system and particle image velocimetry (PIV) measurements. The effects of the structural mass ratio and mass-damping on the VIV amplitude and frequency response are investigated at a constant Reynolds number by manipulating the structural mass, stiffness and damping in the cyber-physical system. The extent of amplitude modulations in VIV is investigated and a new metric is proposed to quantify the extent of amplitude modulations. A methodology for extracting relevant flow physics associated with coherent structures in the flow is presented for VIV data. Low-order models (LOM) are proposed to describe the dynamics of the wake in each of the VIV branches based on the evolution of the modal temporal coefficients obtained from the proper orthogonal decomposition (POD). The low-order modelling approach is re fined by including a phase-averaging term to better model cases where significant spatial oscillations of the velocity field occur.Item Open Access Feasibility Study of a Radial Turbine for a Solar Chimney Power Plant(2018-12-07) Caicedo Flores, Paul Vinicio; Wood, David Howe; Johansen, Craig T.; Morton, Chris R.; Nowicki, Edwin PeterSolar Chimney Power Plants (SCPPs) use solar radiation to increase the temperature of the air creating an airflow which is used to drive one or more turbines. Only one large-scale prototype has been built in Manzanares, Spain. Among other factors, the uniqueness of each location plays against a mass production method for the whole system or specific components. According to the literature review, the cost of the turbine is an average of 15 % of the total investment. This thesis investigates if a radial turbine with sheet steel blades placed at the bottom of the Manzanares SCPP is a cost-effective solution. Three radial turbines are designed and the largest power output achieved is 77.7 kW at 15 rpm for a solar radiation of 850 W/m^2, more than 40 kW higher than the original axial turbine. The thickness of the blades and the Levelized Electricity Cost (LEC) are calculated.Item Open Access Investigation and modeling of shock wave propagation in a shock tube with a partially opened diaphragm(2019-09-17) Alves, Marcel Martins; Bauwens, Luc; Johansen, Craig T.; Azaiez, Jalel; Brinkerhoff, Joshua R.; Morton, Chris R.; Korobenko, ArtemNumerical simulations of high-pressure air, helium, and hydrogen discharging into a low-pressure air section through an orifice, representing a partially opened diaphragm in a shock tube, are performed using OpenFOAM. Synthetic schlieren images are used to visualize the development of shock waves, expansion waves, and mixing layers as the initial pressure ratio, area ratio, jet Reynolds number, and gas driver type are varied. Insight from the simulations are used to develop and assess theoretical shock strength models, based on discharge coefficients for orifice plates in compressible pipe flow and sonic nozzles. Model predictions are compared to an empirical model from the literature to assess performance. Limitations of the models are examined, and simple corrections are proposed to increase the range of applicability. The proposed shock strength models can be used to predict jet-ignition associated with an accidental hydrogen explosion.Item Open Access Modeling and Control of Dynamic Stall Loads on Smart Airfoil(2020-08-26) Mohamed, Ayman Salah Ashry; Wood, David H.; Pieper, Jeffery Kurt; Morton, Chris R.; Ziadé, Paul; Zhou, Qi; Johnson, David AndrewWind turbines operate under challenging inflow conditions, which can affect the turbine loads greatly. The turbine blades subjected to these excessive, fluctuating aerodynamic loads can go into dynamic stall, during which the flow separation is delayed and intense vortex structures are developed. There is no closed-form solution for a dynamic stall, and the present state-of-the-art still shows limitations in modeling and controlling the dynamic stall loads. The present work aims to improve the modeling of dynamic stall loads and to provide simulation tools for mitigating the variation in these loads with the assistance of a trailing edge flap (TEF). A modified version of the extended ONERA dynamic stall model is proposed for predicting unsteady forces, with an emphasis on modeling the effects of the dynamic stall vortex (DSV). The modifications include modeling the chord-axis forces instead of the wind-axis forces that the model was originally developed for. A novel approach for defining the onset of a dynamic stall in the time-marching solution is proposed based on the events taking place during a dynamic stall in the axial force without correlating them empirically. An extensive validation has been implemented on experimental data of different airfoils relevant to wind turbine applications. The results show an excellent correlation with the experimental data, particularly in deep dynamic stall scenarios, during which large fluctuations in the aerodynamic loads appear. The present work included direct, unsteady force measurements on a NACA 643-618 airfoil equipped with TEF (smart airfoil) in both a wind tunnel and water channel. Measurements in the wind tunnel have been used to expand the application of the new dynamic stall model in terms of predicting and controlling the unsteady loads on smart airfoils. The experiment utilizing the water channel investigated the impact of controlling the TEF hinge moment on unsteady loads. In addition, particle image velocimetry (PIV) measurements were carried out to explore the influence of the TEF actuation on the flow field around the smart airfoil. The modified model demonstrates an excellent correlation to the unsteady loads and the associated fluctuation on the smart airfoil despite the change in the effective angle of attack and apparent camber in response to the TEF actuation. The measurements also show that the TEF has a remarkable ability to reduce load variations despite the excessive effort required to control it in the presence of a substantial laminar separation bubble (LSB) and the development of DSVs. Additionally, the results indicate that the TEF hinge moment can be utilized as a localized sensor for unsteady loads and DSV shedding on the smart rotor. Controlling the hinge moment of TEF provides a promising reduction in the variation in the unsteady normal force.Item Open Access Modeling and Evaluation of Wind Turbine Operational Strategies During Icing Events(2019-01-10) Hildebrandt, Shannon; Sun, Qiao; Nowicki, Edwin Peter; Morton, Chris R.; Wood, David H.Cold climates around the world are seeing increasing investment in wind power generation. The benefits of cold regions, however, come with unique challenges that are not experienced by wind turbines in more temperate regions. The accumulation of ice on wind turbine blades in particular can reduce power production due to aerodynamic inefficiencies and turbine shutdowns. To gain a better understanding of the extent to which these challenges are faced across Canada, the author ran a Survey in 2017 of 43 wind farms across the country. Results were presented at the 2018 CanWEA O&M Summit, and discussions that followed highlighted an important and unanswered question: When an icing event is detected or predicted at a wind farm, is it better to pause the turbines during the event or maintain power production? How much less ice is accumulated if the wind turbines are paused, and how does this impact power production? To answer these questions, the Ice and Power Model described herein was developed. Wind turbine characteristics and icing event conditions are taken as inputs, and blade ice accumulation, aerodynamic impacts, and power production impacts are produced as outputs. The model consists of three components: (1) ice accumulation, (2) aerodynamic analysis, and (3) power curve estimation. Upon validation, the model was used to estimate and analyze the blade ice accumulation on the NREL 1.5 MW reference wind turbine for five icing events, in which the input parameters of far-field wind speed, air temperature, cloud liquid water content, and droplet mean volume diameter were varied. For each icing event, two simulations were executed with the model where: (a) the wind turbine maintains operation during the icing event and (b) the wind turbine is paused for the duration of the icing event. The resulting ice accumulation, impacts to blade aerodynamics, and impacts to power production capabilities following the icing event were compared. The results provide evidence that while pausing turbines does indeed result in significantly less ice accumulation, the impact to power production capabilities following the icing event is not significant enough to justify cutting power production to zero for short events.Item Open Access Multi-objective optimization using evolutionary algorithms: Application to the control of flow past a circular cylinder(2018-11-22) Bingham, Conrad Cole; Martinuzzi, Robert John; Morton, Chris R.; Hu, Yaoping; Ziadé, Paul; Westwick, David T.; Epstein, Marcelo D.Modifications to the vortex shedding dynamics from a circular cylinder of diameter D are investigated experimentally in a free surface water channel. The vortex shedding is modified via the placement of a control cylinder of diameter \textit{D}/8 in the vicinity of the main cylinder. A methodology is presented to link changes in the wake dynamics and loading on the main cylinder. The analysis combines Fourier Modal Decomposition, Proper Orthogonal Decomposition, and phase averaging. Based on differences in the wake dynamics, the influence of the control cylinder can be classified according to its placement: (i) in the free stream outside the main cylinder shear layer; (ii) within the main cylinder shear layer; and (iii) in the recirculation region. While fluctuating lift is significantly reduced in all cases, the mean and fluctuating drag are affected differently. A generalized model-free method to optimize parameters for open-loop and closed-loop control in fluid mechanics applications is then presented. A multi-objective evolutionary algorithm (MOEA) is employed to minimize the oscillating lift caused by vortex shedding from the main cylinder. The control cylinder is prescribed a position as well as a periodic motion in two dimensions. The MOEA efficiently handles the larger optimization parameter space. The first objective of the algorithm is to minimize the fluctuating force coefficient $C_{L_{RMS}}$, while the second objective is to minimize of the actuation power required to drive the control cylinder. The final solution suppresses $C_{L_{RMS}}$ by over 90\% using near-zero actuation power. Further, the MOEA automatically provides a sensitivity study as to the influence of the different parameters and also in which spatial area the greatest influence is expressed.Item Open Access Multiphase flow analysis of Desanders Sand Separators(2020-05-13) Basyouny, Ahmed; Wood, David H.; Morton, Chris R.; Hugo, Ronald J.; Johansen, Craig T.; He, Jennifer; Tachie, Mark FrancisMultiphase flows have been a significant problem in the oil and gas industry, with many recent reports of failures in industrial piping and equipment due to erosion either from long-term liquid impingements or solid particles. One of the most efficient horizontal sand separators is the product developed by Specialized Desanders Inc., which is called the “Horizontal Desander.” It is a gravity-based separator, and the associated multiphase flow physics has been investigated in this research. This study analyzes the phase separation by applying multiphase numerical analysis using Star CCM+ software. Experimental testing with the two-phase flow (air and water), and three-phase flow (air, water, and sand) were performed and compared to the numerical results. After confidence is established in the numerical model, a four-phase simulation was performed to analyze the sand distribution at different operating pressures. The Particle Image Velocimetry measurements applied to the two-phase experiment showed that the time-averaged, RMS of velocity fluctuations and the frequency analysis of the air-liquid interface are in an acceptable agreement with the simulation results. Both the experiment and the simulation results have shown that 99% of sand has settled within 54% of the Desander length. The four-phase simulations show that higher operating pressures reduce the liquid level, and this affects the velocity of phases inside the Desander. The velocity changes result in changes to the trajectory of sand particles, causing them to travel further downstream at higher operating pressure. Knowledge of the different phase interactions and behavior of multiphase flow is essential in developing and optimizing gravity separators.Item Open Access Numerical Analysis of Supersonic and Hypersonic Intake Systems with Nanoparticle Injection(2020-01-28) Jagannathan, Rangesh; Johansen, Craig T.; Mohamad, Abdulmajeed Abd; Morton, Chris R.; Hickey, Jean Pierre; Yanushkevich, Svetlana N.Inter-phase momentum and energy transfer interactions in gas-particle flows were studied for applications in high-speed airbreathing engines. The overall aim of the thesis is to investigate nanoparticle injection across high-speed intake systems. In the first stage, existing numerical strategies were assessed for the modeling of compressible, gas-nanoparticle flows. Based on a detailed literature review, a combination of quasi-1D and 3D computational fluid dynamic (CFD) approaches were selected. CFD simulations were conducted using a custom-modified, unsteady, compressible, Eulerian-Lagrangian gas-particle CFD solver in OpenFOAM. A novel solution verification method was developed for predicting numerical uncertainties in multiphase flow simulations with one-way coupling, which was used to verify the CFD solutions. In the second stage, the effect of nanoparticle injection on the performance of supersonic/hypersonic intake systems was investigated. A parametric study using Mach number (M), Stokes number (Stk), particle Eckert number (Ecp), particle mass loading ratio (SL), and thermal transport number (at) was conducted across a quasi-1D converging-diverging (C-D) supersonic intake at idealized and single-shock compression cases. Gains in pressure recovery were observed at specific combinations of the five input parameters, which was further investigated. The 1D study was followed by CFD simulations of a rectangular, mixed-compression intake at Mach 3. The CFD results predicted a 16% gain in pressure recovery, consistent with the 1D model predictions. In the final stage, starting and buzz characteristics of high-speed intakes were investigated with nanoparticle injection. Isentropic and Kantrowitz contraction limits were estimated at particle mass loading ratios of 0, 0.12 and 0.24. These results were followed by CFD simulations of a 2D, external compression intake with an operating Mach number of 2. The CFD study was conducted at particle mass loading ratios of 0, 0.12 and 0.24; and nozzle throttling ratios from 0.57 to 0.44. The effect of nanoparticle injection on the Ferri-type instability and unstart were investigated. The potential for nanoparticles to attenuate buzz, once the instabilities are triggered, was also assessed.Item Open Access Open-loop and Closed-loop control of a Flow over a Cluster of Three Cylinders with Variable Spin Rate in Equilateral Triangular Arrangement(2020-01-30) Zhong, Xiao Peng; Martinuzzi, Robert John; Morton, Chris R.; Li, Simon; Nowicki, Edwin PeterThe control of the flow over a cluster of three rotating cylinders arranged in a triangular configuration (pinball-configuration) is simulated using 2D URANS. The free stream flow impinges onto the front cylinder at Reynolds number of 2054 based on the diameter. Open-loop and closed-loop controls change the flow behavior because the rotating surfaces of the cylinders directly modify the vorticity flux into the wake. For the open-loop control, the leeward cylinders are counter-rotating at a constant rate. In the open-loop control, the strength of the shear layers from the leeward cylinders and the central gap flow change and even reverse as the rotation rate varies. As a result, different and unique flow states were realized. The fluctuation of the flow reaches a minimum at certain rotation ratio (angular velocity of a cylinder non-dimensionalized by free-stream flow velocity). In the closed-loop control, the fluctuating lift of each cylinder is used as a feedback signal to control an oscillatory rotation rate about the mean that is set to match an open-loop configuration. The physical model describing the rotation-induced-lift by oscillatory rotation is developed and reveals a phase lag between 0 to pi from the steady-state-lift. Based on this mechanism, a closed-loop controller is designed such that the rotation-induced-lift partially cancels the lift from the natural vortex shedding. This results in lift attenuation. The closed-loop control is tested on the single cylinder case, revealing that the shear layers are elongated and the strength of the vorticity flux across each shear layer is reduced. The closed-loop control is then applied to the pinball-configuration. The same elongation of the shear layers and the reduction in the strength of vorticity flux are observed. Additionally, the closed-loop control changes the central gap flow, which slightly shifts the flow characteristics accordingly.Item Open Access Tomographic PIV Investigation of the Cantilevered Circular Cylinder Wake with Varying Aspect Ratio and Boundary Layer Thickness(2018-05-23) Crane, Robert; Morton, Chris R.; Martinuzzi, Robert; Zhou, Qi; Ziadé, PaulThis thesis investigates the wake of a finite wall-mounted circular cylinder of diameter D and height H for aspect ratios (H/D) of 3 < H/D < 7 and boundary layer thickness to diameter (delta/D) ratios, 0.98 < delta/D < 1.25 using Tomographic Particle Image Velocimetry. The Reynolds number based on cylinder diameter is held fixed at Re = 750. The primary focus of the study is to characterize the main topological features of the mean field, and elucidate the wake dynamics leading to the mean topology. The results show that for all cases investigated, the mean field topology contains an arch vortex in the near wake and a quadrupole structure in the far wake characterized by a pair of oppositely signed streamwise vorticity concentrations emanating from both the tip and base. The availability of 3D-3C velocity field data facilitates the first known experimental analysis of the time averaged vorticity transport equation and the streamwise evolution of the full vorticity field. The vorticity transport analysis suggests that streamwise vorticity arises due to a 3-dimensional separation and subsequent re-orientation process which occurs inside the arch vortex. The process involves the tilting of y-vorticity and z-vorticity into the streamwise direction, and streamwise amplification via stretching. Proper Orthogonal Decomposition was applied to the 3D velocity field measurements to classify the wake dynamics associated with the mean field topology and to perform a low order reconstruction. For all values of H/D and delta/D studied, the time averaged field and low order model is characterized by a quadrupole and shed full-loops respectively, in agreement with that observed for the square cylinder. Decreasing H/D resulted in: (i) a reduction in circulation of both the tip and base vortices, (ii) a reduction in circulation of the shed full loop structures, (iii) increased frequency modulation of the shed structures resulting in a broadening of the Strouhal peak, (iv) increased modulation in circulation of the full-loop structures across a sampling of shedding cycles, and (v) a reduction in the relative energy content of the first modal pair associated with the fundamental harmonic of vortex shedding. Decreasing delta/D resulted in a reduction in circulation for the base vortices and an increase in circulation for the tip vortices. In the low order model, decreasing delta/D resulted in the arch vortex developing less curvature at the base which occurred over a smaller portion of the cylinder span before the core of the structure was aligned with the cylinder axis. No critical aspect ratio H/D_crit corresponding to the onset of symmetric arch-vortex shedding was identified across the parameter space of the study.Item Open Access Visualizing three-dimensional vortex shedding through evolution surface clusters(2019-11-01) Ferrari, Simon; Hu, Yaoping; Morton, Chris R.; Martinuzzi, Robert JohnTurbulent vortex shedding in the wake of a bluff body often contains cycle-to-cycle variations in the shape, trajectory, and intensity of vortices. Existing flow visualization techniques cannot effectively present these variations and, consequently, their influence on the aerodynamics to the user. This paper explores a new flow visualization approach to represent quasi-periodic vortex shedding over multiple shedding cycles concurrently. This approach uses a reduced-dimension representation of spatiotemporal vortex progression (called evolution surfaces) and ensemble visualization techniques (clustering). The resulting visualization can be used to identify topological changes in the behavior and strengths of coherent structures (i.e. vortices) in unsteady flows. This approach is applied in two case studies of bluff body wakes with Reynolds Numbers Re = 1200 (Hemmati et al. 2016c) and Re = 300 (Morton et al. 2018). In prior work, classification of these wakes’ dynamics was based on energy fluctuation and shedding topology. However, these techniques are not well suited for representing characteristic changes between shedding regimes. In the present work, it has been shown that evolution surface clusters help to identify topological changes characterizing cycle-to-cycle variations in vortex behavior, while reducing visual clutter. The results indicate that evolution surface clusters are a promising visualization tool for comparative analysis of unsteady vortex dynamics in turbulent wakes.