Article
Mechanics
Marlin J. Holmes, Jonathan W. Naughton
Summary: This experimental investigation examines the influence of swirl and wake strength on the evolution of axisymmetric turbulent wake. The results show that an increase in swirl strength leads to an increase in the growth and decay rate constants of the wake, while changes in wake strength have little impact on these rates.
Article
Mechanics
Fengrui Zhang, Yulia T. Peet
Summary: In this study, wake flow past an axisymmetric body of revolution at a diameter-based Reynolds number of 5000 is investigated through direct numerical simulation. Three dominant coherent motions are identified in the wake: vortex shedding motion, bubble pumping motion, and very-low-frequency motion. The vortex shedding pattern follows a reflectional symmetry breaking mode and exhibits a helical spiraling pattern. The bubble pumping motion is confined to the recirculation region and is a result of Gortler instability. The very-low-frequency motion is related to a stochastic destabilisation of a steady symmetric mode and appears as a slow, precessional motion of the wake barycentre.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Environmental Sciences
Yuxin Deng, Min Zhang, Wangqiang Jiang, Letian Wang
Summary: This study introduces a new method for evaluating the electromagnetic scattering coefficient and imaging characteristics of turbulent wakes in the near field, generated using the large-eddy simulation method while controlling different values of net momenta. The results demonstrate that the net momentum transferred to the background flow field determines the development of the turbulent wake, explaining the formation mechanism of turbulence.
Article
Physics, Fluids & Plasmas
Taihang Zhu, Jonathan F. Morrison
Summary: The turbulent axisymmetric bluff body wake is studied using large eddy simulation, with a focus on the effect of pulsed jet forcing. Spectral proper orthogonal decomposition (SPOD) analysis successfully identifies the dominant modes of the wake flow and the impact of pulsed jet forcing.
PHYSICAL REVIEW FLUIDS
(2021)
Article
Mechanics
Khashayar F. Kohan, Susan J. Gaskin
Summary: This study investigates the effect of a zero-mean-flow turbulent ambient on the geometry of the turbulent/turbulent interface (TTI) of an axisymmetric jet and compares it with the traditional turbulent/non-turbulent interface (TNTI). The results show that the ambient turbulence enhances radial transport of concentration and scalar fluctuations within the jet, resulting in steeper mean and root-mean-square scalar conditional jumps across the TTI layer compared with those of the TNTI. The presence of ambient turbulence also stretches and corrugates the interface surface area.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Green & Sustainable Science & Technology
Ashwin Vinod, Cong Han, Arindam Banerjee
Summary: Tidal stream turbines in high-energy tidal sites are affected by turbulent non-homogeneous flow environments, particularly the shear effects caused by turbulent inflow that reduce the power coefficient. The study results show that sheared turbulent inflows lead to increased torque and thrust fluctuations in the turbine model, asymmetry in the near-wake, and gradual effects on wake turbulence and velocity deficit.
Article
Physics, Fluids & Plasmas
Weijun Yin, Shancong Tao, Koji Nagata, Yasumasa Ito, Yasuhiko Sakai, Yi Zhou
Summary: This study numerically analyzes the spatial distribution and organization of coherent structures in a self-similar axisymmetric turbulent wake using data from a previous simulation. The study finds that the radial positions of the turbulent/non-turbulent (T/NT) interface exhibit a self-similar form normalized by the wake width delta at different downstream locations. The Liutex method is used to identify the vortex core center and compute the direction of the vortex axis, revealing preferences and self-similarities in various parameters.
PHYSICAL REVIEW FLUIDS
(2023)
Article
Physics, Fluids & Plasmas
K. S. Kankanwadi, O. R. H. Buxton
Summary: The effect of freestream turbulence on the spreading of the near wake of a circular cylinder is investigated using particle image velocimetry data. It is found that freestream turbulence enhances the entrainment rate into the wake and also enhances wake meandering. The influence of wake meandering is isolated by eliminating the von Karman vortex street, which shows that freestream turbulence suppresses the entrainment rate when large-scale vortices are not present in the wake. Furthermore, the presence of freestream turbulence occasionally leads to a transient elimination of vortex shedding.
PHYSICAL REVIEW FLUIDS
(2023)
Article
Mechanics
Chunyue Zhu, Yujia Tian, Preben Buchhave, Clara M. M. Velte
Summary: This work explores the self-similarity of a free axisymmetric jet in air, specifically in the fully developed region of the jet. Accurate measurements of statistical functions of the axial velocity component are obtained using a laser Doppler anemometer, and these measurements are compared to predictions from a simple jet model. The implications for further study of self-similarity in free jets are discussed.
Article
Mechanics
R. H. Hernandez
Summary: The objective of this work is to present a coherent detection method to determine the relationships between pressure fluctuations and wake velocity in the case of turbulent flow past a cylinder. Experimental results and pressure-velocity statistics are reported, showing the mutual influence between wall pressure and wake velocity fluctuations, as well as the correlation between large scale turbulent vortex shedding and surface pressure fluctuations.
Article
Engineering, Marine
Jagadeshwar Kandula, P. Usha Sri, P. Ravinder Reddy, S. K. Gugulothu
Summary: The primary objective of this research is to study the cavitating effects of fluid flow past different axisymmetric cavitator in the upper sub-critical flow regime. Both experiments and numerical simulations show that an increase in velocity can result in an increase in cavity length and diameter.
SHIPS AND OFFSHORE STRUCTURES
(2022)
Article
Chemistry, Analytical
Hongjiang Cui, Guanxin Chen, Ying Guan, Huimin Zhao
Summary: Due to aerodynamic resistance, aerodynamic noise, and other problems, the development of traditional high-speed electric multiple units (EMUs) on the open line has been restricted, and the construction of a vacuum pipeline high-speed train system has emerged as a new solution. This paper analyzes the turbulent characteristics of the near wake region of EMU in vacuum pipes using the Improved Detached Eddy Simulation (IDDES), establishing the relationship between turbulent boundary layer, wake, and aerodynamic drag energy consumption. The results show the presence of a strong vortex in the wake near the tail, with symmetrical distribution and gradual growth in the downstream propagation. This study provides guidance for the aerodynamic shape optimization design of the vacuum EMU train in the future, contributing to passenger comfort improvement and energy consumption reduction.
Article
Engineering, Marine
M. Dhalwala, A. Bayram, P. Oshkai, A. Korobenko
Summary: This study examines the performance and near-wake characteristics of a full-scale vertical-axis hydrokinetic turbine under different flow conditions. The results show that the turbine's performance is slightly reduced under turbulent inflow, with significant fluctuations in the instantaneous power coefficient. However, turbulent inflow significantly improves wake recovery, which is important for design considerations.
Article
Mechanics
Jiangang Chen, Oliver R. H. Buxton
Summary: This study examines the spatial evolution of the geometrical features of the turbulent/turbulent interface (TTI) in a cylinder wake. Comparisons are made to a turbulent/non-turbulent interface (TNTI) by exposing the wake to various turbulent backgrounds. It is found that the TTI spreads faster towards the ambient flow than the TNTI, and a transition region of the interfaces' spreading is observed. Moreover, the positions of both the TNTI and TTI exhibit non-Gaussian probability density functions (PDFs) in the near wake due to the influence of large-scale coherent motions.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Thermodynamics
Gokturk M. Ozkan, Husnu Egitmen
Summary: The study investigates the flow characteristics and turbulent structures around a NACA0012 airfoil at different Reynolds numbers and angles of attack. The results show significant changes in flow structures with increasing Reynolds number, and these changes have a significant impact on the drag polar of the NACA0012 airfoil.
EXPERIMENTAL THERMAL AND FLUID SCIENCE
(2022)
Article
Engineering, Mechanical
E. Saredi, A. Sciacchitano, F. Scarano
Summary: This study proposes a novel approach for detecting outliers in PIV measurements by comparing the ratio between local advection and turbulent kinetic energy (TKE) production, and shows that it outperforms the state-of-the-art method in terms of accuracy.
EXPERIMENTS IN FLUIDS
(2022)
Article
Mechanics
Wouter G. van Veen, Johan L. van Leeuwen, Bas W. van Oudheusden, Florian T. Muijres
Summary: To generate aerodynamic forces for flight, insects move their wings back and forth at high frequencies. Existing models for aerodynamic forces often simplify the effects of wing-stroke rate and acceleration, which may not capture the complex unsteady aerodynamics. In this study, computational-fluid-dynamics simulations were used to explore the relationship between aerodynamic forces, flow dynamics, wing-stroke rate, wing-stroke acceleration, and wing-planform geometry. A novel unsteady aerodynamic force model was developed and calibrated, which includes improved versions of translational-force and added-mass force models, as well as a third component reflecting the delay in bound-circulation build-up during wing acceleration. The study shows that this effect can be modeled as a stroke-acceleration-dependent correction on the translational-force model. The new model was subsequently applied to realistic wing-beat kinematics of hovering Dipteran insects, demonstrating the substantial contribution of stroke-acceleration-related aerodynamic forces to lift and drag production.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Engineering, Multidisciplinary
M. van Nesselrooij, O. W. G. van Campenhout, B. W. van Oudheusden, F. F. J. Schrijer, L. L. M. Veldhuis
Summary: A wind tunnel drag measurement system has been developed in this study to accurately measure small changes in aerodynamic drag over a flat surface. Experimental tests show that the system achieves high accuracy in different wind tunnels and matches the results from related literature. The flexible structure of this system enables it to be used in most wind tunnels, accelerating the research and development of turbulent drag reduction concepts.
MEASUREMENT SCIENCE AND TECHNOLOGY
(2022)
Article
Engineering, Aerospace
Alessandro D'Aguanno, Ferdinand F. J. Schrijer, Bas W. W. van Oudheusden
Summary: This study experimentally investigates the effects of sweep angle and finite wing on transonic buffet. The results show that buffet oscillations are stronger for airfoil than for finite-span wings. The buffet behavior and oil flow visualizations demonstrate a large difference between airfoil and unswept wing. Spectral analysis reveals that the classical 2-D buffet peak is substantially attenuated in swept wings, while additional contributions appear in a higher frequency range. The PIV results also show a periodical occurrence of a secondary supersonic area downstream of the main shock wave structure for the 30 deg swept wing.
Article
Thermodynamics
Alessandro D'Aguanno, Ferdinand F. J. Schrijer, Bas W. van Oudheusden
Summary: This experimental study investigates the potential of using an upward deflection trailing edge flap (UTEF) to control transonic buffet. Different geometries and dimensions of UTEFs were studied and the results showed that the straight 2% chord UTEF configuration was the most effective in reducing buffet oscillations, while serrated UTEF configuration was found to be ineffective.
FLOW TURBULENCE AND COMBUSTION
(2023)
Article
Engineering, Mechanical
A. D'Aguanno, P. Quesada Allerhand, F. F. J. Schrijer, B. W. van Oudheusden
Summary: In this experimental study, the panel flutter induced by an impinging oblique shockwave at a freestream Mach number of 2 was investigated using planar particle image velocimetry (PIV) and stereographic digital image correlation (DIC). High-speed cameras were used to obtain a time-resolved description of the panel motion and shockwave-boundary layer interaction (SWBLI). The results showed that panel oscillations occurred with a maximum amplitude of ten times the panel thickness, and the dominant frequencies matched the main spectral content of the reflected shockwave position.
EXPERIMENTS IN FLUIDS
(2023)
Article
Engineering, Civil
Constantin Jux, Andrea Sciacchitano, Fulvio Scarano
Summary: The aerodynamic characteristics of a modern road cycling wheel in crosswind were investigated using force- and planar PIV measurements in the TU Delft Open Jet Facility. The performance of a 62 mm deep rim with three tire profiles and yaw angles up to 24 degrees was evaluated. It was found that the rim-tire section of the wheel behaved similar to an airfoil, resulting in a reduction of aerodynamic resistance with increasing yaw angle. This reduction was limited by the stall angle of the tire-rim profile, which was found to depend on the tire's surface structure. Higher stall angles and lower resistance were achieved when the tire profile triggered laminar-to-turbulent boundary layer transition.
JOURNAL OF WIND ENGINEERING AND INDUSTRIAL AERODYNAMICS
(2023)
Article
Engineering, Aerospace
Alessandro D'Aguanno, Ferry Schrijer, Bas van Oudheusden
Summary: This experimental study investigates the use of shock control bumps (SCBs) for controlling transonic buffet. The effects of SCBs with different spanwise array spacings were examined using schlieren visualization and particle image velocimetry. The study found that a spacing of Delta(ySCB) = 25%c was the most efficient in reducing transonic buffet oscillations and reverse flow.
Article
Engineering, Aerospace
Sumit Tambe, Ferry Schrijer, Arvind Gangoli Rao, Leo Veldhuis
Summary: Boundary-layer instability on a rotating cone induces spiral vortices, which have a significant impact on the onset of laminar-turbulent transition. This study investigates the effect of varying cone angle on boundary-layer instability on rotating cones facing axial inflow. It is found that increasing cone angle stabilizes the boundary layer over rotating cones in axial inflow.
Article
Engineering, Aerospace
Xavier Carrillo Corcoles, Christoph Mertens, Andrea Sciacchitano, Bas W. W. van Oudheusden, Roeland De Breuker, Jurij Sodja
Summary: This study conducted an aeroelastic wind-tunnel experiment to investigate the influence of wing stiffness and hinge release threshold on the gust load alleviation performance of a folding wingtip design. The results showed that the structural properties did not have a significant impact on the peak load alleviation, but the hinge release threshold and timing did. Releasing the hinge at the correct timing significantly reduced peak loads, but also affected the system dynamics, decreasing flutter speed and increasing load oscillations.
JOURNAL OF AIRCRAFT
(2023)
Article
Engineering, Aerospace
Christoph Mertens, Jose L. Costa Fernandez, Jurij Sodja, Andrea Sciacchitano, Bas W. van Oudheusden
Summary: The aeroelastic response of the Delft-Pazy wing to steady and periodic unsteady inflow conditions is experimentally analyzed. The nonintrusive measurements are performed with an integrated optical approach that provides combined measurements of the structural response of the wing and the unsteady flowfield around it. The results show that both structural and aerodynamic responses of the wing depend strongly on the frequency of the gust.
Article
Acoustics
Lourenco Tercio Lima Pereira, Francesco Avallone, Daniele Ragni, Fulvio Scarano
Summary: This work discusses the physics and design impact of noise reduction achieved from serrated trailing-edges. An experimental campaign is carried out on a 2D model using different trailing-edge serrations to build a complete dataset of acoustic measurements. Systematic modifications of a reference sawtooth serration design are made to its scale and geometry. The results obtained provide guidelines for serration design choices and their impact on broadband noise reduction.
Article
Thermodynamics
Julio Carrasco Grau, Olaf W. G. van Campenhout, Friso H. Hartog, Michiel van Nesselrooij, Woutijn J. Baars, Ferdinand F. J. Schrijer
Summary: In this study, direct force measurements were used to replicate experiments from the literature and test new array configurations. A total of 23 different protrusion configurations were investigated in a turbulent boundary layer flow. All configurations increased the drag between 2% and 10%, casting doubt on the proposed drag reduction potential of chevron-shaped protrusions.
FLOW TURBULENCE AND COMBUSTION
(2023)
Article
Green & Sustainable Science & Technology
Daan van der Hoek, Joeri Frederik, Ming Huang, Fulvio Scarano, Carlos Simao Ferreira, Jan-Willem Van Wingerden
Summary: Dynamic induction control (DIC) is an effective method to increase the power output of wind farms. This study investigates the wake of a wind turbine under periodic excitation using a wind tunnel experiment. The results show that DIC increases the available power in the wake, and enhanced wake recovery contributes to the increased energy.
WIND ENERGY SCIENCE
(2022)
