Article
Mechanics
Siddharth Gupta, Jisheng Zhao, Atul Sharma, Amit Agrawal, Kerry Hourigan, Mark C. C. Thompson
Summary: The study investigates the 2-D and 3-D wake transitions of a NACA0012 airfoil at different angles of attack and Reynolds numbers. The results show that the transition from 2-D to 3-D flow occurs through a mode C transition. Further instabilities of the 2-D periodic base flow are also observed. The study provides valuable insights into the flow transitions of aerodynamic bodies.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Andrey I. Aleksyuk, Matthias Heil
Summary: We investigate the initial development of three-dimensional mode A instability in the wake behind a circular cylinder. We observe that long-wavelength perturbations organize in a time-shifting pattern, where the in-plane velocity of each streamwise slice corresponds to the base flow solution at shifted times. We analyze the mechanisms governing the growth or decay of these perturbations, emphasizing the crucial role of the tilting mechanism and its non-local interactions similar to Biot-Savart induction. We also discuss the generalization of our findings to other flow types.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
E. Duran Venegas, P. Rieu, S. Le Dizes
Summary: In this work, Joukowski's rotor wake model is applied to a two-blade rotor, providing solutions using a free-vortex method. The analysis includes stability and performance evaluation of the solutions obtained.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
E. J. Grift, M. J. Tummers, J. Westerweel
Summary: This paper presents the results of time-resolved flow field measurements around a realistic rowing oar blade moving through water, along with measurements of hydrodynamic forces acting on the blade. Analysis of the flow field during the drive phase revealed the relationship between leading-edge and trailing-edge vortices and the generation of instationary lift and drag forces for rowing propulsion. Adjusting the angle of the blade attachment improved the alignment of the generated impulse with the propulsive direction, increasing efficiency.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Hongyi Jiang
Summary: The study investigates the three-dimensional wake transition for flow past a diamond cylinder at different Reynolds numbers, revealing variations in wake characteristics such as mode swapping between modes A and B, as well as the gradual disorganization of mode B. It is found that there are major differences in wake properties between a diamond and a circular cylinder, with the decomposition of flow properties aiding in the understanding of these differences. The complex interactions between streamwise and spanwise vortices, as well as the wake transition and base-flow transition, are identified as factors that excite mode B and suppress the subharmonic mode.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Chengjiao Ren, Zinan Liu, Liang Cheng, Feifei Tong, Chengwang Xiong
Summary: This study investigates the three-dimensional wake transitions of a steady flow past two side-by-side circular cylinders by using Floquet analysis and direct numerical simulations. The results show that the wake transitions are similar to the isolated cylinder counterpart at large gap-to-diameter ratios (g*), but become complex at small g*. The characteristics formed in the base flows play a significant role in the complexity of the wake transitions.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Sanjay Mittal, Jawahar Sivabharathy Samuthira Pandi, Mainak Hore
Summary: The study investigates the flow past a cylinder with side walls at various Reynolds numbers and aspect ratios, finding that the complexity of wake transitions increases with aspect ratio. The vortex structures and shedding characteristics change with Reynolds number and aspect ratio, showcasing different flow patterns and shedding modes.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Xiaoyu Shi, Honglei Bai, Md. Mahbub Alam, Chunning Ji, Hongjun Zhu
Summary: The effects of the spanwise wavelength of a sinusoidal wavy cylinder with an elliptic cross-section on wake structures and fluid forces were investigated numerically. Based on vortical structures, Strouhal number, wake closure length, fluid forces, streamline topologies, and spatio-temporal evolutions, five distinct flow patterns were identified. Pattern III had the minimum drag force and zero fluctuating lift force was observed in patterns III and IV. Flow pattern IV showed alternate vortex shedding over half of the wavelength of the wavy elliptic cylinder, leading to zero fluctuating lift over one complete wavelength. A thorough comparison was made between the wakes of the wavy elliptic cylinder and wavy circular or square cylinders, revealing the underlying flow physics behind the observed behaviors.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Jawahar Sivabharathy Samuthira Pandi, Sanjay Mittal
Summary: Numerical simulations of flow past a finite rectangular wing with a NACA 0012 section at different semi-aspect ratios and angles of attack have revealed the presence of streamwise vortices. These vortices become stronger and more numerous as the semi-aspect ratio increases and occupy a larger spanwise extent. The local force coefficients show non-monotonic spanwise variation and the strength of the wing-tip vortex increases for higher semi-aspect ratios. Viscous and pressure drag dominate for low and high semi-aspect ratios respectively, and the time-averaged drag coefficient initially decreases and then increases with increasing semi-aspect ratio. Different types of vortex shedding and dislocations are observed for different semi-aspect ratios and angles of attack.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Negar Hosseini, Martin D. Griffith, Justin S. Leontini
Summary: The study shows that when the pitch between two upstream cylinders is large, the downstream wake exhibits a two-row vortex structure, and the shape of the third body has minimal impact on this structure. However, in certain cases, the position of the third body can disrupt the original vortex structure and globally broadcast its presence.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
An-Kang Gao, Chris D. Cantwell, Onur Son, Spencer J. Sherwin
Summary: In this study, the three-dimensional transition and force characteristics of plunging airfoils are investigated using experimental measurements, numerical simulations, and linear stability analysis. The interaction between the leading-edge vortex (LEV), the previous-cycle LEV (pLEV), and the trailing-edge vortex (TEV) is found to be the primary factor affecting the 3-D transition and associated forces. The results show that different interaction patterns and vortex pairs have different effects on the stability and lift of the LEV, depending on the range of the chord-based Strouhal number St(c).
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
K. Liu, B. F. Zhang, Y. C. Zhang, Y. Zhou
Summary: This study investigates the predominant coherent structures around an Ahmed body in the low-drag regime, identifying five distinct Strouhal numbers in the wake and discussing the formation mechanism and dynamical role of a corner vortex. The research also documents the Reynolds-number effect on the flow and proposes a conceptual flow structure model for a low-drag Ahmed body based on the data collected.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Christopher M. Douglas, Benjamin L. Emerson, Timothy C. Lieuwen
Summary: This paper characterizes the steady and time-periodic behavior of swirling jets using numerical bifurcation analysis. The study reveals a wide array of flow patterns within a certain range of Reynolds number and swirl ratio, showing both stable axisymmetric flows and unstable three-dimensional flow structures. The research highlights the role of unsteady nonlinear interactions on the overall behavior of swirling jets and discusses the similarities and differences between this type of unconfined jet and other classes of swirling flows.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Soumarup Bhattacharyya, Izhar Hussain Khan, Shivam Verma, Sanjay Kumar, Kamal Poddar
Summary: Experimental study on three-dimensional flow past a circular cylinder executing sinusoidal rotary oscillations reveals different wake modes and characteristics influenced by amplitude and forcing frequency, as observed through water tunnel experiments and flow visualization techniques.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Shubham Goswami, Arman Hemmati
Summary: The wake of a wall-mounted finite prism is numerically studied and characterized with different depth ratios and Reynolds numbers, revealing the formation and interaction mechanisms of symmetric and asymmetric wake patterns.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Engineering, Aerospace
Aaron M. Turpin, Daniel Chin, Kenneth Granlund
Article
Physics, Fluids & Plasmas
W. A. Weisler, R. Waghela, K. Granlund, M. Bryant
Summary: The study investigates the lift characteristics of a wing transitioning out of water, showing that starting depth, angle of attack, and egress velocity impact lift generation, while changes in flow attachment also play a significant role in lift production.
PHYSICAL REVIEW FLUIDS
(2021)
Article
Thermodynamics
Rodney Metoyer, Punnag Chatterjee, Kelsey Elfering, Matthew Bryant, Kenneth Granlund, Andre Mazzoleni
Summary: The study introduces a computational model for tethered multirotor axial flow turbines, exploring the equilibrium behavior and hydrostatic state of the system. It reveals that positively buoyant turbines can operate at desired depths and multiple turbine systems can be anchored at a single point for maximum energy production.
ENERGY CONVERSION AND MANAGEMENT
(2021)
Article
Engineering, Multidisciplinary
Aaron M. Turpin, Kenneth O. Granlund, Tatsunori Hayashi, Hirotaka Sakaue
Summary: The feasibility of back-imaging polymer-ceramic pressure-sensitive paint (PC-PSP) has been investigated, showing promising results for overcoming the optical access constraints of conventional PSP imaging techniques. The front and back imaging responses were found to be functionally identical, with minor differences attributed to random noise and material differences. This suggests that back-imaging is a potential method for improving PSP imaging.
MEASUREMENT SCIENCE AND TECHNOLOGY
(2021)
Article
Mechanics
Aaron M. Turpin, Rachelle L. Speth, Scott E. Sherer, Kenneth O. Granlund
Summary: In supersonic flow over a finite-width cavity, shear layer impingement was often biased to one side of the wall, with the possibility of switching sides. The experimental-computational study revealed that this resonance phenomenon led to two asymmetric and stable states.
Article
Engineering, Mechanical
Aaron M. Turpin, Kenneth O. Granlund, Tatsunori Hayashi, Hirotaka Sakaue
Summary: The study constructed a rectangular cavity with a novel downstream-sliding door to analyze resonance evolution through quasi-static and dynamic door openings. The pressure data showed transitions from acoustic resonance to Rossiter-type resonance based on door positions. The spatial distributions of resonance were qualitatively consistent with door positions, suggesting an acoustic standing wave phenomenon.
EXPERIMENTS IN FLUIDS
(2021)
Article
Automation & Control Systems
Andrew Abney, James Reed, Kartik Naik, Samuel Bryant, Dillon Herbert, Zak Leonard, Ashwin Vadlamannati, Mariah Mook, Sumedh Beknalkar, Miguel Alvarez, Kenneth Granlund, Matthew Bryant, Andre Mazzoleni, Hosam Fathy, Chris Vermillion
Summary: This paper presents a closed-loop experimental framework and dynamic model validation for a 1/12-scale underwater kite design. The framework significantly expands upon any previously developed open-source framework for experimental underwater kite characterization by involving fully actuated, closed-loop controlled kite and flexible tether. It allows for the validation of three closed-loop flight control strategies and a critical comparison between dynamic model predictions and experimental results.
JOURNAL OF DYNAMIC SYSTEMS MEASUREMENT AND CONTROL-TRANSACTIONS OF THE ASME
(2022)
Article
Mechanics
Kelsey Elfering, Shreyas Narsipur, Kenneth Granlund
Summary: The ratio between streamwise airfoil oscillations and the freestream velocity in the reduced frequency range relevant to unsteady applications has not been well studied. In this study, a parameter study was conducted to understand the dependence of circulatory lift on angle of attack, Reynolds number, surge amplitude, and reduced frequency. The results showed that unsteady lift is dependent on Reynolds number and reduced frequency, and the deviation between theory and experiment increases with increasing velocity fluctuation. A detailed study of surge amplitude of 0.5 was conducted to better understand this deviation.
Article
Engineering, Marine
Kelsey Elfering, Rodney Metoyer, Punnag Chatterjee, Andre Mazzoleni, Matthew Bryant, Kenneth Granlund
Summary: A coaxial turbine with significant rotor spacing under skew offers increased power output compared to a flow-aligned turbine, thanks to a freestream velocity region experienced by the downstream rotor called the fresh flow region. A lab-scale prototype was built to compare the skew-to-power relationship of the coaxial turbine system to a blade element momentum theory model with sheared streamtubes representing the fresh flow region. The inclusion of the fresh flow region in the theoretical analysis improves the accuracy of predicting torque and power performance.
Proceedings Paper
Engineering, Marine
Vinson Oliver Williams, Samuel Bryant, Saurabh Agrawal, Andre P. Mazzoleni, Kenneth Granlund, Praveen Ramaprabhu, Matthew Bryant
Summary: This study suggests that tethered coaxial turbines (TCTs) can be used to extract hydrokinetic energy from the Gulf Stream's flow. The operating point and power extraction capabilities of TCTs are determined by hydrodynamic and electromechanical analyses. A case study demonstrates the performance and optimal operating point of TCTs under different flow conditions.
2022 OCEANS HAMPTON ROADS
(2022)
Proceedings Paper
Engineering, Marine
Saurabh Agrawal, Vinson Oliver Williams, Xinyang Tong, Mehedi Hassan, Mike Muglia, Matthew Bryant, Kenneth Granlund, Praveen Ramaprabhu, Andre P. Mazzoleni
Summary: This paper presents a prototype of a towed dual rotor coaxial turbine designed to demonstrate the ability of underwater hydrokinetic devices to harvest energy from ocean currents. Preliminary test results show the system's power extraction, robustness, and waterproofing capabilities.
2022 OCEANS HAMPTON ROADS
(2022)
Proceedings Paper
Engineering, Marine
Mehedi Hassan, Matthew Bryant, Andre Mazzoleni, Praveen Ramaprabhu, Kenneth Granlund
Summary: This paper develops and validates a novel wake model for coaxial dual-rotor turbines, which can accurately estimate the wake velocity deficit in the near- and far-wake of the turbine. By contrasting the wake prediction with CFD results, it is found that the model shows good agreement with the simulations. The study reveals the practical significance of this model in solving the layout optimization problem of dual-rotor turbines.
2022 OCEANS HAMPTON ROADS
(2022)
Article
Engineering, Aerospace
Maria A. Aleman, Ashok Gopalarathnam, Kenneth Granlund
JOURNAL OF AIRCRAFT
(2022)
Article
Engineering, Aerospace
William D. Gothard, Kenneth O. Granlund
Summary: 100 drop tests were conducted to study the store separation of a generic missile. Trajectories were grouped into two primary groups using machine learning techniques and statistical analysis, providing strong evidence of bifurcation.
JOURNAL OF AIRCRAFT
(2022)
Article
Engineering, Aerospace
Daniel Chin, Aaron Turpin, Kenneth Granlund
JOURNAL OF AIRCRAFT
(2020)