Article
Mechanics
Davide Modesti, Srikanth Sathyanarayana, Francesco Salvadore, Matteo Bernardini
Summary: This study investigates the characteristics of supersonic turbulent channel flow over cubical roughness elements through direct numerical simulation. The results show that the Mach number has a significant impact on the mean velocity profile, while the thermal field is substantially affected by the roughness.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Thermodynamics
Umberto Ciri, John Michael B. Tubije, Miguel A. Guzman-Hernandez, Sylvia Rodriguez-Abudo, Stefano Leonardi
Summary: Numerical simulations were conducted to study turbulent oscillatory flow over a bed of fixed spherical particles. The effects of particle size and Reynolds number on the flow were investigated. Results showed that the flow behavior over the rough bed differed from the classical Stokes' solution for laminar boundary layers. Turbulence was observed during deceleration phases, with a logarithmic layer in the velocity profile, and canonical distribution of Reynolds shear stress and turbulent kinetic energy production. Anisotropy maps showed similar distributions to unidirectional wall-bounded flows when the flow was fully developed.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2023)
Article
Mechanics
Rong Ma, Karim Alame, Krishnan Mahesh
Summary: The numerical simulation reveals that the influence of a rough bottom wall on flow mainly manifests in the roll-up of the shear layer in the wall-normal direction. There is a strong correlation between the height of random short wave roughness and wall shear stress, depending on the local roughness topography.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
M. Gul, B. Ganapathisubramani
Summary: This study investigates the flow characteristics of a turbulent boundary layer over different sand-grain roughness created by different sandpapers. The results show self-similarity in flow properties within a certain range, regardless of transitional or fully rough conditions. Despite differences in turbulence profiles, large-scale structures across all locations remain independent of roughness parameters.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Mostafa Aghaei-Jouybari, Junlin Yuan, Zhaorui Li, Giles J. Brereton, Farhad A. Jaberi
Summary: Direct numerical simulations were used to investigate the effects of roughness on supersonic turbulent channel flows. Results show that the turbulence is strongly influenced by the roughness topography and the associated shock patterns. Two-dimensional (2-D) roughness generates strong oblique shock waves, while three-dimensional (3-D) roughness results in weaker shocklets. The impingement of shocks on the wall leads to localized augmentations of turbulence shear production. The entropy generation and temperature values are higher in 2-D roughness cases compared to 3-D ones. The effects of roughness extend beyond the near-wall layer due to the presence of shocks.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Engineering, Multidisciplinary
Witold Elsner, Artur Drozdz, Ewa Szymanek, Artur Tyliszczak, Pawel Niegodajew
Summary: The effects of surface roughness and pressure gradient on turbulent boundary layer development were investigated in this study. The results showed that higher amplitude of the 2D wavy surface increased turbulence production and led to earlier separation of the TBL. In contrast, the 3D topography resulted in a greater streamwise velocity deficit, lower growth of velocity fluctuations, and smaller and less energetic structures downstream of the corrugation compared to the 2D case.
APPLIED MATHEMATICAL MODELLING
(2022)
Article
Engineering, Civil
Danny Dunbar, Dominic A. van der A, Tom O'Donoghue, Pietro Scandura
Summary: A novel empirical model for the streamwise velocity in oscillatory boundary layer flow in the rough turbulent regime is presented. The model is based on simple expressions that require only the free-stream velocity time-series and the equivalent sand-grain roughness length of the bed. The model assumes a frequency-independent attenuation and phase lead for all flow harmonics, and these expressions are obtained from previous experimental studies. Only the oscillating component of the flow is considered, and steady streaming is neglected. The model predicts kinematic errors that are typically two orders of magnitude smaller than the maximum oscillatory velocity in the free-stream, making it suitable for engineering applications.
COASTAL ENGINEERING
(2023)
Article
Mechanics
Ioannis K. Kaminaris, Elias Balaras, Michael P. Schultz, Ralph J. Volino
Summary: This study investigates the evolution of turbulent boundary layers over truncated cones in both staggered and random configurations using direct numerical simulations. The computational results are validated using experimental measurements and show a good agreement. The presence of secondary flows in the cross-stream plane is observed in both staggered and random arrangements, with the momentum pathways approaching the edge of the boundary layer in random arrangements. The correlation between the momentum pathways and the leading edge of the roughness is clear, while the correlation to the local topography is weak.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Thermodynamics
M. Farzaneh, N. Zgheib, S. A. Sherif, S. Balachandar
Summary: We used a turbulence-informed physics-based model to study frost buildup on a flat plate under turbulent flow conditions. By varying the plate temperature, free-stream temperature, and humidity ratio, we found that the Nusselt and Sherwood numbers are independent of these parameters and proposed a method to estimate the temporal evolution of the frost layer. Additionally, a sensitivity analysis on frost layer density, thermal conductivity, and Schmidt number was conducted.
INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER
(2022)
Article
Mechanics
Junji Huang, Lian Duan, Meelan M. Choudhari
Summary: This study investigates the spatial evolution of flat-plate zero-pressure-gradient turbulent boundary layers over long streamwise domains at high Mach numbers and cold-wall conditions using direct numerical simulations. The study monitors the settlement of turbulence statistics into a fully developed equilibrium state and characterizes the streamwise evolution of various important variables.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Y. Kuwata
Summary: This study investigates the turbulent heat transfer over a rough surface using direct numerical simulations. The effects of different parameters on the heat transfer process are discussed. By analyzing the spatial and time-averaged momentum and energy equations, the mechanisms behind the influence of friction Reynolds number and relative roughness on turbulent heat transfer are revealed.
Article
Thermodynamics
Vidya Vishwanathan, Daniel J. Fritsch, K. Todd Lowe, William J. Devenport
Summary: Experimental investigations were conducted on non-equilibrium, turbulent boundary layers over rough and smooth surfaces. The primary effect of roughness was to increase the magnitude of the outer layer and skin friction parameters. Flows over both wall conditions exhibited history effects in the integrated boundary layer parameters, which indicates characteristic dependencies on the streamwise flow evolution. Indirect skin friction methods for non-equilibrium rough wall flows were sensitive to the regression fits of the empirical data, which were used in the absence of direct measurements. The effective sandgrain roughness parameter, ks, remained independent of pressure gradient flow history, within the uncertainty of empirical methods used for skin friction determination. Varying levels of wall-similarity were observed in the smooth and rough wall Reynolds stress profiles.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2023)
Article
Engineering, Aerospace
Giacomo Della Posta, Marco Fratini, Francesco Salvadore, Matteo Bernardini
Summary: This study presents direct numerical simulations of a turbulent boundary layer on a microramp to investigate the impact of Mach number on the flow. The study finds that the flow topology changes significantly due to compressibility effects and the typical wake features are not linearly scaled with the geometry dimensions but depend on the incoming flow conditions. Furthermore, the study explores the spectral content in time and space of the wake, with Kelvin-Helmholtz instability dominating along the shear layer. The shedding onset is postponed and exhibits a lower peak frequency that evolves in space for larger Mach numbers.
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
Himani Garg, Lei Wang, Guillaume Sahut, Christer Fureby
Summary: In the last decade, progress in Additive Manufacturing (AM) has allowed for the development of optimized heat exchangers for more sustainable products. However, the rough surfaces created by AM techniques differ from those used in prior research, posing challenges in using current wall models in numerical simulations. To address this, a high-fidelity Large Eddy Simulation (LES) database was built to develop and assess novel wall models for AM. The study focused on turbulent flow in rough pipes built from AM surfaces and revealed the impact of roughness parameters on turbulence.
Article
Mechanics
Guangchen Shen, Junlin Yuan, Mantha S. Phanikumar
JOURNAL OF FLUID MECHANICS
(2020)
Article
Physics, Fluids & Plasmas
Zvi Hantsis, Ugo Piomelli
PHYSICAL REVIEW FLUIDS
(2020)
Article
Mechanics
S. Pargal, J. Yuan, G. Brereton
Summary: This paper investigates the transition process in turbulent channel flow using small-span direct numerical simulation, and applies it to flow with riblets. Comparisons with full-span cases on a smooth wall show that the small-span simulation captures the essential dynamics satisfactorily. In the case of riblet flow, riblets do not fundamentally affect the flow dynamics but delay the retransition process due to milder streak meandering.
JOURNAL OF TURBULENCE
(2021)
Article
Mechanics
Gianmarco D'Alessandro, Zvi Hantsis, Cristian Marchioli, Ugo Piomelli
Summary: This study investigates the accuracy of bed-load transport models when combined with high-resolution Navier-Stokes solvers. It discusses the impact of different stress distributions on the transport model prediction, and finds that for small Shields parameters, coarser methods may yield more accurate predictions, while short-time averaging of fluid forces on sediments can improve prediction accuracy.
INTERNATIONAL JOURNAL OF MULTIPHASE FLOW
(2021)
Article
Mechanics
Sai C. Mangavelli, Junlin Yuan, Giles J. Brereton
Summary: The dynamic effects of roughness geometry on the response of half-height turbulent channel flow to impulse acceleration were investigated using direct numerical simulations. The thickness of the roughness sublayer remains almost constant on rough walls, with ensemble-average flows staying close to equilibrium inside. Turbulence rapidly develops within the sublayer, leading to substantial changes in the Reynolds stress balance.
JOURNAL OF TURBULENCE
(2021)
Article
Mechanics
G. J. Brereton, M. Aghaei Jouybari, J. Yuan
Summary: The study focused on the Reynolds-averaged modeling of turbulent boundary-layer flow over various rough surfaces based on direct numerical simulations. The most effective approach was found to be modeling the roughness sublayer as a prescribed velocity profile, either at a coarse or fine level. Calculations using sandgrain roughness wall functions and velocity-profile models showed good agreement with simulation data and friction coefficients for a wide range of flow conditions.
Article
Mechanics
Saurabh Pargal, Hao Wu, Junlin Yuan, Stephane Moreau
Summary: By comparing the results of direct numerical simulations of incompressible turbulent boundary layers, it is found that the effect of mild wall curvature on velocity and wall-pressure statistics is masked by the presence of adverse pressure gradients in most of the boundary layer development, except for regions with weak pressure gradients or thick boundary layers where the effect of wall curvature interacts with that of adverse pressure gradients.
Article
Environmental Sciences
Guangchen Shen, Junlin Yuan, Mantha S. Phanikumar
Summary: In this study, direct numerical simulation (DNS) results of hyporheic exchange on a flat river bed with different particle roughness textures are reported. The transit time distributions (TTDs), subsurface flow patterns, and interfacial volumetric fluxes were discussed. The results showed that bed roughness induced deep subsurface flow paths and affected transit times. The study also considered the impact of molecular diffusion on transit times. This work demonstrates the significant hyporheic exchange induced by particle roughness on a macroscopically flat sediment bed.
WATER RESOURCES RESEARCH
(2022)
Article
Mechanics
Francesco Ambrogi, U. Piomelli, D. E. Rival
Summary: This study uses large-eddy simulation to analyze a spatially developing turbulent boundary layer affected by a space- and time-dependent pressure gradient. The study finds that reducing the frequency significantly impacts the flow separation process, with high frequencies resulting in thinner separation bubbles compared to steady conditions and low frequencies triggering growth in the wall-normal direction.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Physics, Fluids & Plasmas
Mostafa Aghaei-Jouybari, Jung -Hee Seo, Junlin Yuan, Rajat Mittal, Charles Meneveau
Summary: The force partitioning method is used to analyze the pressure-induced drag for turbulent flow over rough walls. The study quantifies the contributions of rotation-dominated vortical regions and strain-dominated regions to the pressure drag, and investigates the effects of surface geometry on drag. The results suggest that the phi field, which encodes surface geometry, can be used to parametrize the surface drag.
PHYSICAL REVIEW FLUIDS
(2022)
Article
Mechanics
S. C. Mangavelli, J. Yuan
Summary: This paper discusses the influence of wall roughness on turbulence statistics and structure, and reveals the significant role of form-induced velocity in turbulent pressure fluctuations and structural changes of turbulent eddies.
JOURNAL OF TURBULENCE
(2023)
Article
Mechanics
Mostafa Aghaei-Jouybari, Junlin Yuan, Zhaorui Li, Giles J. Brereton, Farhad A. Jaberi
Summary: Direct numerical simulations were used to investigate the effects of roughness on supersonic turbulent channel flows. Results show that the turbulence is strongly influenced by the roughness topography and the associated shock patterns. Two-dimensional (2-D) roughness generates strong oblique shock waves, while three-dimensional (3-D) roughness results in weaker shocklets. The impingement of shocks on the wall leads to localized augmentations of turbulence shear production. The entropy generation and temperature values are higher in 2-D roughness cases compared to 3-D ones. The effects of roughness extend beyond the near-wall layer due to the presence of shocks.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
A. Caiazzo, S. Pargal, H. Wu, M. Sanjose, J. Yuan, S. Moreau
Summary: This study investigates the wall-pressure and velocity statistics in the turbulent boundary layer on a cambered controlled-diffusion aerofoil. The results show that the presence of strong adverse pressure gradients affects the turbulent flow characteristics significantly, and different normalisations are analyzed to study trailing-edge noise and other statistics. The strong adverse pressure gradient increases the intensity of low-frequency wall-pressure fluctuations, shortens the streamwise coherence of wall-pressure fluctuations in time and space, and reduces the convection velocity.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Physics, Fluids & Plasmas
Ming Teng, Ugo Piomelli
Summary: This study numerically investigates the development of secondary instabilities in a boundary layer over a backward-facing step. The results show that the step height and the imposed freestream-velocity distribution significantly influence the transition process, leading to different transition characteristics in different cases.
Article
Mechanics
Mostafa Aghaei Jouybari, Junlin Yuan, Giles J. Brereton, Michael S. Murillo
Summary: This study investigates the effect of surface roughness on turbulent flow by developing a high-fidelity prediction approach using deep neural network and Gaussian process regression machine learning methods. The predicted equivalent sand-grain height for turbulent flows over various rough surfaces showed high accuracy compared to existing prediction formulas, with surface porosity and roughness slope identified as important factors in drag prediction.
JOURNAL OF FLUID MECHANICS
(2021)