Article
Acoustics
Chung-Hao Ma, Manuj Awasthi, Danielle Moreau, Con Doolan
Summary: This paper presents a combined experimental and numerical study on the aeroacoustics of low Mach number turbulent flow over a forward-backward facing step (FBS). The study investigates the influence of step length and aspect ratio on wall pressure fluctuations and noise production. The results show that the largest wall pressure fluctuations occur slightly downstream of the step leading edge and turbulence interactions contribute to the wall pressure fluctuations in the on-step reattachment region. Aeroacoustic beamforming results show that the dominant noise source is located at the step leading edge.
JOURNAL OF SOUND AND VIBRATION
(2023)
Article
Thermodynamics
Abd Rahim Abu Talib, Ali Kareem Hilo
Summary: The study found that combining a corrugated wall with a BFS channel can significantly enhance heat transfer, but also increases friction. The channel with a 4mm amplitude height and 20mm wavelength performed the best at 5000 Re, reaching a performance evaluation criterion factor of 1.33.
CASE STUDIES IN THERMAL ENGINEERING
(2021)
Article
Mechanics
Q. Luo, G. Dolcetti, T. Stoesser, S. Tait
Summary: The water surface response to turbulent flow over a backward-facing step is investigated using high-resolution large-eddy simulation (LES). The LES method is validated using experimental data and the analysis reveals the interplay between turbulence structures and the dynamics of the water surface. The water surface deformation is mainly influenced by gravity waves and turbulence-driven forced waves. The study highlights the importance of decomposing water surface fluctuations to understand the underlying flow structure dynamics.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Thermodynamics
Paul Pouech, Florent Duchaine, Thierry Poinsot
Summary: The study focuses on ignition in subsonic, high-speed flows of premixed methane/air mixture, evaluating the Minimum Ignition Energy (MIE) and studying ignition by a spark placed in the recirculation zone. DNS is used to measure flame stabilization energy and propose criteria for ignition success, showing that flame stretch on the flame elements leaving the recirculation zone plays a major role.
COMBUSTION AND FLAME
(2021)
Article
Thermodynamics
J. Morita, H. Mamori, T. Miyazaki
Summary: Direct numerical simulations were conducted to investigate the incompressible turbulent flow over a backward-facing step. The application of a traveling wave-like body force control on the top surface of the step was used to control the separation flow. The results showed that both stationary wave cases and traveling wave cases could decrease the reattachment length, but in different patterns. The oscillation of the separation bubble in the traveling wave cases was dominated by the period of the traveling wave. The switch between negative and positive body forces played a key role in the release of the separation bubble.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2022)
Article
Chemistry, Multidisciplinary
Bostjan Zajec, Marko Matkovic, Nejc Kosanic, Jure Oder, Blaz Mikuz, Jan Kren, Iztok Tiselj
Summary: This paper investigates the comparison of two very accurate approaches, PIV and DNS, in 3D turbulent flow experiments, aiming to reveal the similarities and differences between the two methods in the same cross-section geometry.
APPLIED SCIENCES-BASEL
(2021)
Article
Mechanics
Danny Dunbar, Dominic A. A. van der A, Pietro Scandura, Tom O'Donoghue
Summary: The hydrodynamics of turbulent oscillatory flow over a gravel-based irregular rough wall is studied using experimental measurements and numerical simulation. Four different flow shapes are investigated, and the results show good agreement with previous studies. Evidence of Prandtl's secondary flows and turbulence structures are observed. Non-Gaussian turbulence statistics are observed near the wall. The results provide valuable insights into the characteristics of turbulent oscillatory flow over a rough wall.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Shabnam Mohammadshahi, Hadi Samsam-Khayani, Zhiwen Deng, Kyung Chun Kim
Summary: This study investigated the velocity distribution and flow dynamics of oscillating jets in confined and non-confined channels, finding that the oscillation frequency is independent of the external domain, while the spreading angle is affected by Reynolds number and AR, leading to the formation of vortices in the confined external domain.
EUROPEAN JOURNAL OF MECHANICS B-FLUIDS
(2021)
Article
Computer Science, Interdisciplinary Applications
Sarvesh Kumar, Amitesh Kumar
Summary: In this study, the influence of sidewalls on a three-dimensional turbulent wall jet is investigated using experimental and numerical approaches. The results show that the sidewalls significantly affect the temperature and velocity distribution, and generate turbulent heat flux and Reynolds stress. The numerical results are in good agreement with the experimental results, indicating that the sidewall configuration leads to an increase in the decay of maximum streamwise velocity and a decrease in the decay of centerline temperature.
COMPUTERS & FLUIDS
(2022)
Article
Thermodynamics
Di Yang, Bin Sun, Tiankai Xu, Binbin Liu, Hongwei Li
Summary: Nanofluids play a significant role in reducing the temperature of the bottom surface downstream of microchannels, with higher volume fractions leading to increased heat transfer coefficients. Increasing the step height enhances heat transfer efficiency, although it also results in higher flow resistance.
APPLIED THERMAL ENGINEERING
(2021)
Article
Engineering, Aerospace
Wen-Chung Wu, Ankit Kumar
Summary: In this study, the flow characteristics of nanofluid over a backward facing step at low Reynolds number were numerically investigated, and the heat transfer was analyzed. The results showed that the use of nanofluid increased the heat transfer coefficient and Nusselt number, while decreasing the coefficient of skin friction and outlet temperature.
Article
Engineering, Aerospace
Yaozhi Zhou, Zun Cai, Qinglian Li, Chenyang Li, Mingbo Sun, Shaotian Gong
Summary: This study experimentally investigated the effects of the backward-facing step and injection schemes on the spray characteristics of a liquid jet in a tandem backward-facing step cavity for the first time. High-speed photography and Schlieren techniques were used to accurately capture the instantaneous structures of the spray and wave structures of the air-flow field. The study revealed complex wave structures in the tandem backward-facing step cavity and found that the injection scheme near the upstream inlet had a higher penetration depth but lower spray distribution for the short cavity, while the injection scheme near the cavity had more spray distribution. For the long cavity, both the injection scheme near the upstream inlet and near the sharp corner of the backward-facing step had better spray distribution. The optimized injection scheme for the long backward-facing step cavity-based combustor is the upstream wall transverse injection, which improves both penetration and spray distribution.
AEROSPACE SCIENCE AND TECHNOLOGY
(2023)
Article
Engineering, Multidisciplinary
Mohamad Klazly, Gabriella Bognar
Summary: This study numerically investigates laminar flow in a micro-sized backward-facing step channel for water-based nanofluids. The impact of temperature differences between the inlet and the downward wall temperatures is also studied. The results show that increasing the concentration of nanoparticles can enhance the velocity and shear stress, as well as improve the heat transfer rate. However, a high volume fraction of nanoparticles decreases the performance efficiency.
ALEXANDRIA ENGINEERING JOURNAL
(2022)
Article
Thermodynamics
Rouhollah Moosavi, Reza Moltafet, Cheng-Xian Lin, Po-Ya Abel Chuang
Summary: The study focuses on the unsteady flow and natural convection heat transfer of fractional Maxwell viscoelastic fluid over sudden expansion geometry, showing that the fractional derivative parameters and physical parameters have significant effects on Nusselt number, friction coefficient, velocity, and temperature.
THERMAL SCIENCE AND ENGINEERING PROGRESS
(2021)
Article
Engineering, Mechanical
Dandan Yang, Sida He, Lian Shen, Xianwu Luo
Summary: In this study, large eddy simulation coupled with immersed boundary method was used to simulate a backward facing step flow, showing slightly over-prediction in reattachment compared to DNS results. However, second-order statistics were in good agreement with reference data, verifying the accuracy of the method.
PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART C-JOURNAL OF MECHANICAL ENGINEERING SCIENCE
(2021)
Article
Thermodynamics
Navid Freidoonimehr, Azadeh Jafari, Maziar Arjomandi
Summary: In this study, a high-fidelity flow visualisation technique is used to investigate the resemblance between a turbulent boundary layer generated by different tripping devices in a lab environment and a naturally developed canonical turbulent boundary layer. The study finds that the blockage created by trips is the main factor affecting the turbulence statistics at a certain downstream distance.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2024)
Article
Thermodynamics
Yuning Wang, Alberto Solera-Rico, Carlos Sanmiguel Vila, Ricardo Vinuesa
Summary: This study proposes a method that combines 6-VAEs for modal decomposition and transformer neural networks for temporal-dynamics prediction in the latent space to develop reduced-order models (ROMs) for turbulent flows. The method achieves high reconstruction accuracy and accurate prediction of temporal dynamics.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2024)
Article
Thermodynamics
L. Laguarda, S. Hickel, F. F. J. Schrijer, B. W. van Oudheusden
Summary: Wall-resolved large-eddy simulations were used to investigate the Reynolds number effects in supersonic turbulent boundary layers at Mach 2.0. The study covered a wide range of friction Reynolds numbers and identified trends in various statistics and scaling laws. The size and topology of turbulent structures in the boundary layer were examined, with a focus on the outer-layer motions at high Reynolds numbers. The study also assessed the influence of outer-layer structures on near-wall turbulence and the sensitivity of uniform momentum regions to compressibility.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2024)
Article
Thermodynamics
A. Doehring, T. Kaller, S. J. Schmidt, N. A. Adams
Summary: In this study, well-resolved large-eddy simulations were used to investigate turbulent duct flows with a square cross section. The influence of a modified wall shear stress on the secondary flow was analyzed by artificially modifying the wall shear stress at one of the four walls. The results showed that the modification led to an asymmetrical distribution of the secondary flow source terms, affecting the momentum distribution. Furthermore, the anisotropy of the Reynolds stress tensor, which induces the secondary flow vortices, was significantly affected by the wall shear stress modulation.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2024)
