Article
Mechanics
Ben Steinfurth, Julien Weiss
Summary: The experimental study investigated the interaction between starting jets and a steady cross-flow, finding different flow structures when compressed air is injected into a rectangular outlet. The results can aid in the selection of appropriate actuation parameters in active mixing and separation control.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Physics, Fluids & Plasmas
Girish K. Jankee, Bharathram Ganapathisubramani
Summary: In flow control, using an array of synthetic jet actuators is more practical than a single actuator. Through a parametric study, it was found that twin jets operated at a specific phase difference and spacing can be more efficient for flow entrainment and momentum distribution.
PHYSICAL REVIEW FLUIDS
(2021)
Article
Mechanics
Michael N. Stavropoulos, Matteo Mancinelli, Peter Jordan, Vincent Jaunet, Joel Weightman, Daniel M. Edgington-Mitchell, Petronio A. S. Nogueira
Summary: Spatial linear stability analysis is used to study the axisymmetric screech tones generated by twin converging round nozzles. Different waves supported by the flow at different conditions are identified using vortex-sheet and finite-thickness models. The frequency-wavenumber regions at which the upstream-propagating guided jet modes are neutrally stable vary with solution symmetry, jet separation, S, and the velocity profile. Screech-frequency predictions from both models agree well with experimental data, but the predictions from the finite-thickness model match the measured screech tones better than the vortex sheet. The present results suggest that the feedback loop generating these screech tones is similar to that observed for single-jet resonance.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Nuclear Science & Technology
Peng Wang, Peiyao Qi, Dongdong Yuan, Xiaoxuan Zhang, Sichao Tan, Dongyang Li
Summary: This research applied 2D Particle Image Velocimetry to study the behavior of nine parallel plane jets in a plate-type fuel assembly under non-blocking and blocking conditions. Analysis revealed the spreading of vortices and the characteristic frequency evolution caused by blockages.
ANNALS OF NUCLEAR ENERGY
(2022)
Article
Physics, Multidisciplinary
KrishnaKumar Rajnath Yadav, Akshoy Ranjan Paul, Anuj Jain
Summary: The study investigated the effects of single-offset and dual-offset twin air-intakes at various inlet Reynolds numbers using synthetic jets. Results showed that slotted synthetic jets can significantly reduce flow separation and enhance static pressure recovery. Furthermore, the single-offset twin air-intake exhibited less total pressure loss compared to the dual-offset one for all Reynolds numbers.
EUROPEAN PHYSICAL JOURNAL PLUS
(2021)
Article
Physics, Fluids & Plasmas
Marc Isele, Kay Hofmann, Artur Erbe, Paul Leiderer, Peter Nielaba
Summary: We investigate the lane formation in nonequilibrium systems of colloidal particles moving in parallel that are driven by gravity. By using particle types with different diameters but equal mass density, a difference in driving force acting on the colloids can be achieved. We find that the larger particles push the smaller particles to the walls, resulting in exclusively small particle lanes at the walls. Additionally, we analyze the mechanisms by which the lanes form and identify system parameter values that foster lane formation.
Article
Mechanics
Giuseppe Anaclerio, Tommaso Capurso, Marco Torresi
Summary: Green hydrogen is expected to play a key role in achieving a carbon-neutral society, especially in the transportation sector. This study investigates the gas-dynamic and mixing characteristics of hydrogen jets exiting from non-axisymmetric cross-sections, aiming to provide guidelines for designing advanced hydrogen injectors for internal combustion engines. The results reveal differences in shock wave systems and gas-dynamic mechanisms among different cross-sections, as well as non-uniformity in radial expansion and axial penetration of the jets.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Cheolgyun Jung, Minho Song, Daegyoum Kim
Summary: This study investigates the formation of a starting jet through a novel eversion process using a vortex generator model. By varying geometric and kinematic parameters, such as the length and bending rigidity of the everting sheets, the study examines their effects on the deformation of the sheets and the formation of the jet. The interaction between the starting jet and the everting sheets enables a faster jet with an improved hydrodynamic impulse to be developed within a shorter stroke time.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Shirin Patil, Srikrishna Sahu
Summary: The paper reports on spray characterization in a novel twin-jet airblast injector, focusing on the effect of injector air swirl on droplet characteristics and dispersion behavior. The addition of air swirl significantly affects spray topology and droplet size downstream of the injector exit, leading to improved atomization quality and high spray dispersion. The results provide insight into the physics behind the improved atomization due to air swirl and demonstrate the injector's ability to achieve atomization quality and high spray dispersion over a wide operating range.
Article
Mechanics
M. Mosavati, R. Balachandar, R. M. Barron
Summary: This study focuses on the behavior of self-oscillating twin jets in a narrow cavity, with computational fluid dynamics simulations revealing significant effects of nozzle spacing on oscillation frequency and turbulence characteristics. Comparison between round and square twin jets showed minimal impact of nozzle shape on jet decay, while twin oscillating jets were found to produce higher turbulence intensity over a wider area, potentially beneficial for cooling hot devices in industrial applications.
Article
Physics, Fluids & Plasmas
N. Offeddu, W. Han, C. Theiler, T. Golfinopoulos, J. L. Terry, E. Marmar, C. Wuthrich, C. K. Tsui, H. de Oliveira, B. P. Duval, D. Galassi, D. S. Oliveira, D. Mancini
Summary: In this work, the poloidal and parallel properties of turbulent filaments in tokamak configurations were characterized using scrape-off layer diagnostics. The results showed an increase in filament velocity and size with increasing core density. The findings were consistent with the two-region model and also provided insight into the parallel filament extension.
Article
Engineering, Marine
Minh N. Doan, Takuya Kawata, Shinnosuke Obi
Summary: This study conducted monoscopic particle image velocimetry measurements of the near-wake of two cross-flow hydrokinetic turbines in six different counter-rotating configurations and found a correlation between flow field structures and power output. The effects of each parameter of the counter-rotating configurations were discussed, providing guidelines for setting up multiple devices in a power farm.
JOURNAL OF MARINE SCIENCE AND ENGINEERING
(2021)
Article
Engineering, Chemical
Stephen Barilovits, Saad A. Khan, Eunkyoung Shim
Summary: This study experimentally investigated the fiber and web formation process of an array of annular meltblown spinnerets. It was found that smaller fibers in cooler air streams require shorter die-collector distances to form bonded fabrics, and the polymer spinning temperature is largely determined by air temperature. The study also showed that processing conditions related to fiber diameter distribution, with median diameters ranging from less than 1 μm to almost 14 μm.
INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH
(2021)
Article
Engineering, Mechanical
Hongxin Wang, Degang Xu, Linwen Li, Kaiwen Zhou, Xin Wen, Hui Tang
Summary: This paper presents a numerical study on the mixing process and near-wall impact of in-line twin synthetic jets (SJs) in a flat-plate laminar boundary layer. It is found that the early stage injection mainly contributes to the formation of the hairpin legs and the injection near the maximum blowing contributes to the formation of the hairpin head. The upstream actuator emitted hairpin vortex has better coherence than the downstream actuator emitted vortex. The findings provide valuable information for the applications of synthetic jets in heat transfer, mixing control, and flow control in a crossflow.
Article
Chemistry, Physical
Meng Yue, Jingwang Yan, Huamin Zhang, Qiong Zheng, Xianfeng Li
Summary: The study suggests that flow channel design can improve the performance of trapezoid flow batteries by reducing polarization and capacity loss. Furthermore, the impact of parameters such as channel depth and electrode porosity on flow patterns is discussed, highlighting the importance of further geometrical optimization.
JOURNAL OF POWER SOURCES
(2021)
Article
Engineering, Aerospace
Felix Gstrein, Bin Zang, Yannick D. Mayer, Mahdi Azarpeyvand
Summary: This experimental study investigates the effect of biologically inspired finlets on reducing the trailing-edge noise of a NACA 0012 airfoil. The study shows that at a specific Reynolds number, the finlets can effectively reduce the trailing-edge noise, and the optimal finlet height to boundary-layer thickness ratio for achieving the highest noise reduction is discussed. The study also reveals the flow dynamics through the finlet-treated area and examines the impact of finlets on static pressure and dynamic pressure fluctuations. The research findings provide valuable insights for potential optimization of finlets.
Article
Thermodynamics
X. Liu, B. Zang, M. Azarpeyvand
Summary: The study experimentally confirmed that the use of trailing-edge sawtooth serrations in a tandem aerofoil configuration can effectively reduce wake-aerofoil interaction noise, indicating a reduction of approximately 10 dB at the 'head-on' wake impingement. Detailed near-field measurements further revealed the flow dynamics associated with the noise reduction, highlighting the interaction primarily occurs within the first 30% of the chord close to the leading-edge area.
EXPERIMENTAL THERMAL AND FLUID SCIENCE
(2022)
Article
Engineering, Aerospace
A. Cheawchan, M. A. Mohamed, B. F. Ng, T. H. New
Summary: The flow past a backward facing ramp (BFR) with rectangular vane-type vortex generators (VGs) located upstream has been investigated numerically. The effects of single and multiple VGs with different skew angles on flow separation behavior were studied. The results show that single VGs generate counter-rotating streamwise vortices, while multiple VGs under the same condition intensify this behavior and lead to significant changes in the distribution of wall shear stress. The distortion of the flow separation region by symmetric/asymmetric streamwise vortices is clarified based on velocity component analysis. The trajectories and characteristics of the streamwise vortices support the idea that they behave significantly more non-linearly at a skew angle of 30° and that different types of vortices result in distinct flow separation control characteristics.
AEROSPACE SCIENCE AND TECHNOLOGY
(2022)
Article
Engineering, Aerospace
J. A. Branch, B. Zang, M. Azarpeyvand, D. Jones, E. Jinks, M. Fernandino Westin
Summary: This study investigates the hydrodynamic near-field of a NACA 16-616 aerofoil across various angles-of-attack, distinguishing pre-stall, stall, and post-stall flow regimes. It reveals that the NACA 16-616 aerofoil stalls by an abrupt leading-edge mechanism, with a secondary significant trailing-edge separation mechanism in the pre-stall regime. Both mechanisms have a significant impact on the unsteady surface pressure.
AERONAUTICAL JOURNAL
(2022)
Article
Engineering, Aerospace
X. F. Wei, L. P. Chua, Z. B. Lu, H. D. Lim, R. Mariani, Y. D. Cui, T. H. New
Summary: This study compares the effects of beveled and double-beveled circular nozzles on supersonic jet screech and finds that beveled nozzles can eliminate screech while double-beveled nozzles amplify it, producing highly unstable screech.
JOURNAL OF AEROSPACE ENGINEERING
(2022)
Article
Optics
Jie Wang, Siwen Ye, Shengxian Shi, T. H. New
Summary: A calibration framework is established for an unfocused light-field camera and a robotic arm, and the mapping relationship between a point light source and its corresponding plenoptic disc feature is established. The method calculates the intrinsic and extrinsic parameters of the camera and solves the transformation matrices for eye-to-hand and eye-in-hand configurations. The proposed calibration method enables 3D reconstruction of calibration boards in different poses and discusses calibration uncertainty in detail.
JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION
(2022)
Article
Instruments & Instrumentation
Shengxian Shi, Linlin Sun, Yinsen Luan, Rui Wang, T. H. New
Summary: This letter discusses the design and implementation of a multi-wavelength light-field pyrometer, which utilizes a CMOS sensor to capture six-channel radiation images. By placing a filter array in front of the main lens, discrete wavelength and radiation intensity can be simultaneously recorded. Experimental results demonstrate the extraction of multi-channel radiation images from a raw light-field multispectral image, and the accurate recovery of a 2D temperature distribution using optimization algorithms.
REVIEW OF SCIENTIFIC INSTRUMENTS
(2022)
Article
Engineering, Aerospace
A. Cheawchan, M. A. Mohamed, B. F. Ng, T. H. New
Summary: This study investigates the streamwise vortex structures produced by wishbone vortex generators (VGs) and their interactions with a backward-facing ramp (BFR), with a focus on understanding their impact on BFR flow separation behavior. The results show that wishbone VGs produce weaker streamwise vortices closer to the BFR surface compared to vane-type VGs. Interestingly, the interaction between multiple streamwise vortices produced by the wishbone VG array is more significant, potentially leading to larger reductions in reattachment length and considerable pressure drag reduction levels.
JOURNAL OF AEROSPACE ENGINEERING
(2023)
Article
Mechanics
Felix Gstrein, Bin Zang, Mahdi Azarpeyvand
Summary: This study demonstrates that biologically inspired finlet treatments can effectively reduce trailing-edge noise on flat plates, making them a promising technology for noise suppression in engineering applications. Through detailed experiments and analysis, the researchers investigated the near-field dynamics of the flow field and the noise-reduction mechanism of the finlet surface treatments. They found that the interaction between the finlets and the flow generated "finlet-induced turbulence," which effectively reduced the unsteady wall-pressure fluctuations and resulted in a broadband reduction of trailing-edge noise. The study also confirmed the existence of an optimal distance between the finlets and the trailing-edge for maximum mixing effects.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Optics
Zhou Zhao, Chunhui Yao, Shengxian Shi, T. H. New
Summary: This work presents a forward ray-tracing method based on Gaussian optics principles to determine the spatial resolution of optical field cameras in PIV. It also proposes a universal evaluation criterion suitable for all three LF-PIV configurations, providing guidance on configuring and selecting optical parameters in practical implementations.
JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION
(2023)
Article
Mechanics
Guanjiang Chen, Bin Zang, Mahdi Azarpeyvand
Summary: A numerical investigation is conducted to study the aerodynamic noise of flow past a circular cylinder with different spanwise lengths. The results show good agreements with experimental and literature data. The spanwise length has limited influence on the power spectral density of the near-field velocity and pressure fluctuations, but substantial differences are observed for the spanwise pressure coherence and near-wake structures. The study emphasizes the importance of sufficient spanwise lengths in predicting noise from flow past a cylinder.
Article
Engineering, Aerospace
Mohamed A. Mohamed, Tze H. New, Bing F. Ng
Summary: The study models the injection of Halon 1301 into a helicopter engine nacelle to investigate dispersion behavior and complex flow physics. A 1-D pipe model is used to simulate the nitrogen-pressurized flow of Halon 1301, and ANSYS Fluent is used to model the injection process. The study evaluates the cooling effect of the agent and the flow dynamics in different flight regimes. Rating: 8 out of 10.
PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART G-JOURNAL OF AEROSPACE ENGINEERING
(2023)
Article
Engineering, Aerospace
Tze How New, Zhen Wei Teo, S. Li, Z. A. Ong, Bjoern Nagel
Summary: The flow behavior and aerodynamic performance of a small-scale joined-wing UAV were investigated under different pitch and yaw angles in subsonic flow conditions. Numerical simulations were compared with experimental results obtained through oil flow visualizations and force measurements. The results revealed the formation of symmetric vortex roll-ups near the fuselage under zero-yaw conditions, but no evidence of such vortices was observed under combined pitch and yaw conditions. Instead, asymmetric flow separations occurred over the fuselage's port side, and they became more complex and interacted with the fuselage and wings as the yaw angle increased. The study also documented the contributions of different pitch and yaw angle combinations to lift and drag coefficients, as well as the flight stability of the UAV.
Article
Engineering, Aerospace
Mohamed Arif Mohamed, Zhen Wei Teo, Tze How New, Bing Feng Ng
Summary: The ability to predict engine exhaust characteristics is important for determining the heat signatures on aircraft components. In this study, the predictions of four turbulence models were compared to particle image velocimetry results for a scaled helicopter engine exhaust. All four models were able to capture the general shape of the exhaust, but failed to accurately describe the shift of the predicted plume from the experiments. A visual correlation using principal component analysis showed quantifiable shifts in the predicted plume mean-centers compared to the measurements. The realizable k-ε model performed the best in matching the statistical variance of the plume distribution, while the SST k-ω and Durbin models performed the best in predicting the bivariate distribution of the plume.
PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART G-JOURNAL OF AEROSPACE ENGINEERING
(2023)
Article
Engineering, Aerospace
U. S. Vevek, Bin Zang, T. H. New
Summary: In this study, a new family of rational mapping functions g(RM)(omega;k,m,s) is introduced for seventh-order WENO schemes. It has been demonstrated that the mapped WENO scheme WENO-RM(6,3,2 x 10(3)), which uses the mapping function g(RM)(omega;6,3,2 x 10(3)), outperforms both WENO-M and WENO-IM(2,0.1) at seventh order. The proposed scheme also performs better at a number of one-dimensional inviscid gas flow problems compared to other popular WENO schemes such as the WENO-Z scheme.
