This paper discusses the numerical investigation of the wall roughness effect on the supercritical water flow susceptible to heat transfer deterioration (HTD). The simulation was carried in the vertical circular pipe using the SST k-omega turbulence model for different sets of heat flux (220kW/m2 & 1810kW/m2) and mass flow rate (0.0106kg/s &0.022kg/s) at a maximum pressure of 25.3MPa. The presence of roughness was incorporated as a uniform sand-grain roughness on the heated wall. As a result, HTD recuperated gradually as the roughness height (Ks) was increased. The mitigation of HTD is a direct consequence of the increase in turbulent kinetic energy (TKE). In contrast, the delay in the onset of HTD is due to the decrease in the dominant forces (buoyancy or acceleration effects) responsible for HTD occurrence. An equivalent thermal resistance model was proposed to elucidate the same. Additionally, the heat transfer coefficient reduces (HTDn) near the outlet at higher roughness values where HTD has completely recovered. This is attributed to the high specific heat value around the pseudocritical temperature. In the end, the efficacy of the roughness was analyzed using two methods: entropy generation and thermal performance factor. Both techniques suggest that the use of rough pipe is beneficial. However, the first method recommends using a Ks value greater than the critical roughness height (Ksc): as the total entropy generation was found to peak at Ksc because of the thermal conductivity variation with temperature. The study revealed high sensitivity of maximum wall temperature and HTD onset to roughness presence. In addition, contrary to usual HTD, a new type of heat transfer impairment (HTDn) can occur without any loss of TKE.
A theoretical model is proposed to explain the roughness characteristics of an ice surface grown from a gravity and wind-driven supercooled water film flowing over an inclined plane. The effects of the water supply rate, plane slope and air stream velocity on the spacing and height of ice surface roughness are investigated from a new type of morphological instability of the ice-water interface. The proposed macro-scale morphological instability under a supercooled water film is quite different from the micro-scale one which results in dendritic growth. It was found that ice surface roughness s…
The correct description of the surface water dynamics in the model of shallow water requires accounting for friction. To simulate a channel flow in the Chezy model the constant Manning roughness coefficient is frequently used. The Manning coefficient n M is an integral parameter which accounts for a large number of physical factors determining the flow braking. We used computational simulations in a shallow water model to determine the relationship between the Manning coefficient and the parameters of small-scale perturbations of a bottom in a long channel. Comparing the transverse water veloc…
In this paper, we study the flow physics underlying the recently developed remote sensing capability of detecting oceanic microplastics, which is based on the measurable surface roughness reduction induced by the presence of microplastics on the ocean surface. In particular, we are interested in whether this roughness reduction is caused by the microplastics as floating particles, or by the surfactants which follow similar transport paths as microplastics. For this purpose, we experimentally test the effects of floating particles and surfactants on surface roughness, quantified by the mean squ…
The current resurgence in the phase diagram study beyond the critical point has questioned the conventional belief of supercritical fluid as a single phase with varying properties. On the same line, a novel two-phase approach has been proposed to study the supercritical flow with heat transfer deterioration (HTD) phenomena. The Volume of Fluid (VOF) multiphase model has been used to analyze the flow, and the simulation result reasonably predicts the wall temperature peaks. Moreover, the velocity and turbulent kinetic energy profiles for different axial locations explain the occurrence of HTD, …
We make time resolved velocity measurements of steel spheres in free fall through liquid using a continuous ultrasound technique. We explore two different ways to induce large changes in drag on the spheres: 1) a small quantity of viscoelastic polymer added to water and 2) altering the surface of the sphere. Low concentration polymer solutions and/or a pattern of grooves in the sphere surface induce an early drag crisis, which may reduce drag by more than 50 percent compared to smooth spheres in pure water. On the other hand, random surface roughness and/or high concentration polymer solutions…
Data assimilation has been applied to coastal hydrodynamic models to better estimate system states or parameters by incorporating observed data into the model. Kalman Filter (KF) is one of the most studied data assimilation methods whose application is limited to linear systems. For nonlinear systems such as hydrodynamic models a variation of the KF called Ensemble Kalman Filter (EnKF) is applied to update the system state in the context of Monte Carlo simulation. In this research, a dual EnKF approach is used to simultaneously estimate state (water surface elevation) and parameters (bottom ro…
Interfacial hydrodynamic slippage of water depends on both on surface chemistry and roughness. This study tries to connect the effect of chemical property and the physical structure of the surface on the interfacial slippage of water. By performing molecular dynamics simulations (MDS) of Couette flow of water molecules over a reduced Lennard-Jones (LJ) surface, the velocity profile is obtained and extrapolated to get the slip lengths. The slip lengths are measured for various surface-fluid interactions. These interactions are varied by changing the wettability of the surface (characterized by …
A type of discrete Boltzmann model for simulating shallow water flows is derived by using the Hermite expansion approach. Through analytical analysis, we study the impact of truncating distribution function and discretizing particle velocity space. It is found that the convergence behavior of expansion is nontrivial while the conservation laws are naturally satisfied. Moreover, the balance of source terms and flux terms for steady solutions is not sacrificed. Further numerical validations show that the capability of simulating supercritical flows is enhanced by employing higher order expansion…
Geothermal energy is an infinite energy source for the present human society. Energy extraction from the deep subsurface requires engineering using a working fluid that circulates between well doublet. Due to its thermal properties, CO2 is an ideal option as a heat transfer fluid. By using CO2, working fluid loss is an advantage compared to other working fluids. This study developed a field-scale hydro-thermal model to examine the heat extraction potential from Soultz-sous-Forêts with CO2 as the working fluid. Results are compared for the same scenario with water as the working fluid. A better…
We report Particle Image Velocimetry of the Large Scale Circulation and the viscous boundary layer in turbulent thermal convection. We use two parallelepipedic Rayleigh-B{é}nard cells with a top smooth plate. The first one has a rough bottom plate and the second one has a smooth one so we compare the rough-smooth and the smooth-smooth configurations. The dimensions of the cell allow to consider a bi-dimensional mean flow. Lots of previous heat flux measurements have shown a Nusselt--Rayleigh regime transition corresponding to an increase of the heat flux in presence of roughness which is highe…
The problem of choice of boundary conditions are discussed for the case of numerical integration of the shallow water equations on a substantially irregular relief. In modeling of unsteady surface water flows has a dynamic boundary partitioning liquid and dry bottom. The situation is complicated by the emergence of sub- and supercritical flow regimes for the problems of seasonal floodplain flooding, flash floods, tsunami landfalls. Analysis of the use of various methods of setting conditions for the physical quantities of liquid when the settlement of the boundary shows the advantages of using…
We experimentally investigate the influence of alternating rough and smooth walls on bubbly drag reduction (DR). We apply rough sandpaper bands of width $s$ between $48.4\,mm$ and $148.5\,mm$, and roughness height $k = 695\,μm$, around the smooth inner cylinder (IC) of the Twente Turbulent Taylor-Couette facility. Between sandpaper bands, the IC is left uncovered over similar width $s$, resulting in alternating rough and smooth bands, a constant pattern in axial direction. We measure the DR in water that originates from introducing air bubbles to the fluid at (shear) Reynolds numbers $\textit{…
We performed non-equilibrium Molecular Dynamics simulations of water flow in nano-channels with the aim of discriminating {\it static} from {\it dynamic} contributions of the solid surface to the slip length of the molecular flow. We show that the regularization of the slip length divergence at high shear rates, formerly attributed to the wall dynamics, is controlled instead by its static properties. Surprisingly, we find that atomic displacements at the Angstrom scale are sufficient to remove the divergence of the slip length and realize the no-slip condition. Since surface thermal fluctuatio…
The analytical study of long wave scattering in a canal with a rapidly varying cross-section is presented. It is assumed that waves propagate on a stationary current with a given flow rate. Due to the fixed flow rate, the current speed is different in the different sections of the canal, upstream and downstream. The scattering coefficients (the transmission and reflection coefficients) are calculated for all possible orientations of incident wave with respect to the background current (downstream and upstream propagation) and for all possible regimes of current (subcritical, transcritical, and…
Superhydrophobic surfaces have been shown to produce significant drag reduction in both laminar and turbulent flows by introducing an apparent slip velocity along an air-water interface trapped within the surface roughness. In the experiments presented within this study, we demonstrate the existence of a surface tension gradient associated with the resultant Marangoni flow along an air-water interface that causes the slip velocity and slip length to be significantly reduced. In this study, the slip velocity along a millimeter-sized air-water interface was investigated experimentally. This larg…
A spectrogram of a ship wake is a heat map that visualises the time-dependent frequency spectrum of surface height measurements taken at a single point as the ship travels by. Spectrograms are easy to compute and, if properly interpreted, have the potential to provide crucial information about various properties of the ship in question. Here we use geometrical arguments and analysis of an idealised mathematical model to identify features of spectrograms, concentrating on the effects of a finite-depth channel. Our results depend heavily on whether the flow regime is subcritical or supercritical…
Some effects of surface tension on fully-nonlinear, long, surface water waves are studied by numerical means. The differences between various solitary waves and their interactions in subcritical and supercritical surface tension regimes are presented. Analytical expressions for new peaked travelling wave solutions are presented in the case of critical surface tension. The numerical experiments were performed using a high-accurate finite element method based on smooth cubic splines and the four-stage, classical, explicit Runge-Kutta method of order four.
Direct numerical simulations (DNS) are performed for two wall-bounded flow configurations: laminar Couette flow at $Re=740$ and turbulent channel flow at $Re_τ=180$, where $τ$ is the shear stress at the wall. The top wall is smooth and the bottom wall is a realistically rough superhydrophobic surface (SHS), generated from a three-dimensional surface profile measurement. The air-water interface, which is assumed to be flat, is simulated using the volume-of-fluid (VOF) approach. The laminar Couette flow is studied with varying interface heights $h$ to understand the effect on slip and drag reduc…
In gravel-bed rivers, bedload transport exhibits considerable variability in time and space. Recently, stochastic bedload transport theories have been developed to address the mechanisms and effects of bedload transport fluctuations. Stochastic models involve parameters such as particle diffusivity, entrainment and deposition rates. The lack of hard information on how these parameters vary with flow conditions is a clear impediment to their application to real-world scenarios. In this paper, we determined the closure equations for the above parameters from laboratory experiments. We focused on…
Scientific Machine Learning of Flow Resistance Using Universal Shallow Water Equations with Differentiable Programming
Department of Civil and Environmental Engineering, Pennsylvania State University, University Park, Pennsylvania, USA 16802（宾夕法尼亚州立大学土木与环境工程系，大学公园，宾夕法尼亚州，美国 16802）；Institute of Computational and Data Sciences, Pennsylvania State University, University Park, Pennsylvania, USA 16802（宾夕法尼亚州立大学计算与数据科学研究所，大学公园，宾夕法尼亚州，美国 16802）
The estimation of the maximum wave sunup height is a problem of practical importance. Most of the analytical and numerical studies are limited to a constant slope plain shore and to the classical Nonlinear Shallow Water (NSW) equations. However, in nature the shore is characterized by some roughness. In order to take into account the effects of the bottom rugosity various ad-hoc friction terms are usually used. In this paper we study the effect of the roughness of the bottom on the maximum runup height. A stochastic model is proposed to describe the bottom irregularity and its effect is quanti…
Water flow model on vegetated hillslopes with erosion
“Gheorghe Mihoc-Caius Iacob” Institute of Mathematical Statistics and Applied Mathematics of the ROMANIAN ACADEMY（罗马尼亚科学院“格奥尔基·米霍克-卡尤斯·雅各布”数学统计与应用数学研究所）
SWASHES: a compilation of Shallow Water Analytic Solutions for Hydraulic and Environmental Studies
Université de Nice – Sophia Antipolis（尼斯-索菲亚安提波利斯大学）；Institut Jean le Rond d’Alembert, CNRS & UPMC Université Paris 06（让·勒朗·达朗贝尔研究所，法国国家科学研究中心与巴黎第六大学）；Université d’Orléans（奥尔良大学）；INRA（法国国家农业研究院）；National University of Ireland, Galway（爱尔兰国立高威大学）
