Showing papers on "Open-channel flow published in 2020"

Hydrodynamic and thermal analysis of water, ethylene glycol and water-ethylene glycol as base fluids dispersed by aluminum oxide nano-sized solid particles

Abstract: The purpose of this paper is to carry out a hydrodynamic and thermal analysis of turbulent forced-convection flows of pure water, pure ethylene glycol and water-ethylene glycol mixture, as base fluids dispersed by Al2O3 nano-sized solid particles, through a constant temperature-surfaced rectangular cross-section channel with detached and attached obstacles, using a computational fluid dynamics (CFD) technique. Effects of various base fluids and different Al2O3 nano-sized solid particle solid volume fractions with Reynolds numbers ranging from 5,000 to 50,000 were analyzed. The contour plots of dynamic pressure, stream-function, velocity-magnitude, axial velocity, transverse velocity, turbulent intensity, turbulent kinetic energy, turbulent viscosity and temperature fields, the axial velocity profiles, the local and average Nusselt numbers, as well as the local and average coefficients of skin friction, were obtained and investigated numerically.,The fluid flow and temperature fields were simulated using the Commercial CFD Software FLUENT. The same package included a preprocessor GAMBIT which was used to create the mesh needed for the solver. The RANS equations, along with the standard k-epsilon turbulence model and the energy equation were used to control the channel flow model. All the equations were discretized by the finite volume method using a two-dimensional formulation, using the semi-implicit method for pressure-linked equations pressure-velocity coupling algorithm. With regard to the flow characteristics, the interpolation QUICK scheme was applied, and a second-order upwind scheme was used for the pressure terms. The under-relaxation was changed between the values 0.3 and 1.0 to control the update of the computed variables at each iteration. Moreover, various grid systems were tested to analyze the effect of the grid size on the numerical solution. Then, the solutions are said to be converging when the normalized residuals are smaller than 10-12 and 10-9 for the energy equation and the other variables, respectively. The equations were iterated by the solver till it reached the needed residuals or when it stabilized at a fixed value.,The result analysis showed that the pure ethylene glycol with Al2O3 nanoparticles showed a significant heat transfer enhancement, in terms of local and average Nusselt numbers, compared with other pure or mixed fluid-based nanofluids, with low-pressure losses in terms of local and average skin friction coefficients.,The present research ended up at interesting results which constitute a valuable contribution to the improvement of the knowledge basis of professional work through research related to turbulent flow forced-convection within channels supplied with obstacles, and especially inside heat exchangers and solar flat plate collectors.

Heat transfer analysis of channel flow of MHD Jeffrey fluid subject to generalized boundary conditions

Abstract: Free convective, unsteady flow of Jeffrey liquid under the influence of magnetic field between two hot upright parallel plates fixed in porous medium is investigated in this paper. First plate is moving with time-dependent velocity $$U_of(t)$$ in its own plane while other is fixed. Mathematical model is developed using law of conservation of momentum, Fourier’s law of heat transfer. Equations for temperature and velocity fields are reduced to dimensionless form by applying suitable dimensionless variables. The Laplace transform method is used to find exact solutions of temperature and velocity. Finally, we have presented the effects of material and flow parameters and illustrated graphically. As a result, through this study, we found that coefficient of heat transfer shows dual behavior for small and large time. Also, the obtained results are reduced to the recently published work.

Rearrangement of secondary flow over spanwise heterogeneous roughness

Abstract: Turbulent flow over a surface with streamwise-elongated rough and smooth stripes is studied by means of direct numerical simulation (DNS) in a periodic plane open channel with fully resolved roughness. The goal is to understand how the mean height of roughness affects the characteristics of the secondary flow formed above a spanwise heterogeneous rough surface. To this end, while the statistical properties of roughness texture as well as the width and spacing of the rough stripes are kept constant, the elevation of the smooth stripes is systematically varied in different simulation cases. Utilizing this variation, three configurations – representing protruding, recessed and an intermediate type of roughness – are analysed. In all cases, secondary flows are present and the skin friction coefficients calculated for all the heterogeneous rough surfaces are meaningfully larger than what would result from the area-weighted average of those of homogeneous smooth and rough surfaces. This drag increase appears to be linked to the strength of the secondary flow. The rotational direction of the secondary motion is shown to depend on the relative surface elevation. The present results suggest that this rearrangement of the secondary flow is linked to the spatial distribution of the spanwise-wall-normal Reynolds stress component, which carries opposing signs for protruding and recessed roughness.

Numerical and perturbation solutions of third-grade fluid in a porous channel: Boundary and thermal slip effects

Abstract: The steady flow of a third-grade fluid due to pressure gradient is considered between parallel plane walls which are kept at different temperatures. The space between the plane walls is assumed to be a porous medium of constant permeability. The viscosity of the fluid is taken as constant as well as a function of temperature. It is further assumed that the fluid may slip at the wall surfaces. The consequence of this assumption results in non-linear boundary conditions at the plane walls. The temperature field is also supposed to satisfy thermal slip condition at the walls. The governing equations are modelled under these assumptions and the approximate solution is obtained using the perturbation theory. The skin friction coefficient is a decreasing function of slip parameters in the case of temperature-dependent viscosity models while no variation is noted for the case of constant viscosity via boundary slip parameter. The heat transfer rate increases with the boundary slip parameter and decreases with the thermal slip parameter. The validity of the approximated solution is checked by calculating the numerical solution as well. The absolute error is calculated and listed in tabular form in the case of constant and temperature-dependent viscosity via boundary and thermal slip parameters. The influence of various emerging parameters on flow velocity and temperature profile is discussed through graphs.

Experimental Study of the Nonlinear Flow Characteristics of Fluid in 3D Rough-Walled Fractures During Shear Process

Abstract: To understand the influence of shear on the hydraulic properties of rock fractures, shear-flow tests were carried out on rock fractures with different surface roughnesses. Each rough-walled fracture was replicated in four specimens, which were sheared at different displacements under normal stresses that varied from 0.5 to 2.0 MPa. At each shear displacement, a series of hydraulic tests with different hydraulic gradients were performed, and the nonlinear flow regimes of the fluid within the fractures were investigated. The results show that Forchheimer’s law can well describe the nonlinear relationship between the flow rate and the hydraulic gradient in rough-walled fractures. Both the linear coefficient and nonlinear coefficient decrease during shearing but increase as the normal stress increases. The critical hydraulic gradient increases with an increase in the shear displacement and normal stress. With an increase in the joint roughness coefficient, the critical hydraulic gradient decreases. The normalized transmissivity exhibits a strong correlation with the Reynolds number. As the shear displacement increases, the fitted curves of the normalized transmissivity versus the Reynolds number shift upward but the curves shift downward with an increase in normal stress. Additionally, the Forchheimer coefficient decreases with an increase in the shear displacement but increases with an increase in the applied normal stress. Visualization tests show that the number of flow paths is large when the shear displacement is small due to various distributions of the contact areas and that the flow of dyed water over the entire fracture decreases. As the shear displacement increases, the flow resistance decreases due to the shear dilation-induced increase in the aperture, and the advantage channel flow is distinct in the fracture. The contact ratio rapidly decreases as the shear displacement increases from 1 to 3 mm and then slightly varies with a continuously increasing maximum shear displacement of 9 mm.

Oblique stripe solutions of channel flow

Abstract: With decreasing Reynolds number, Re, turbulence in channel flow becomes spatio-temporally intermittent and self-organises into solitary stripes oblique to the mean flow direction. We report here the existence of localised nonlinear travelling wave solutions of the Navier–Stokes equations possessing this obliqueness property. Such solutions are identified numerically using edge tracking coupled with arclength continuation. All solutions emerge in saddle-node bifurcations at values of Re lower than the non-localised solutions. Relative periodic orbit solutions bifurcating from branches of travelling waves have also been computed. A complete parametric study is performed, including their stability, the investigation of their large-scale flow, and the robustness to changes of the numerical domain.

Symmetric mhd channel flow of nonlocal fractional model of btf containing hybrid nanoparticles

Abstract: A nonlocal fractional model of Brinkman type fluid (BTF) containing a hybrid nanostructure was examined. The magnetohydrodynamic (MHD) flow of the hybrid nanofluid was studied using the fractional calculus approach. Hybridized silver (Ag) and Titanium dioxide (TiO2) nanoparticles were dissolved in base fluid water (H2O) to form a hybrid nanofluid. The MHD free convection flow of the nanofluid (Ag-TiO2-H2O) was considered in a microchannel (flow with a bounded domain). The BTF model was generalized using a nonlocal Caputo-Fabrizio fractional operator (CFFO) without a singular kernel of order α with effective thermophysical properties. The governing equations of the model were subjected to physical initial and boundary conditions. The exact solutions for the nonlocal fractional model without a singular kernel were developed via the fractional Laplace transform technique. The fractional solutions were reduced to local solutions by limiting α → 1 . To understand the rheological behavior of the fluid, the obtained solutions were numerically computed and plotted on various graphs. Finally, the influence of pertinent parameters was physically studied. It was found that the solutions were general, reliable, realistic and fixable. For the fractional parameter, the velocity and temperature profiles showed a decreasing trend for a constant time. By setting the values of the fractional parameter, excellent agreement between the theoretical and experimental results could be attained.

Resolvent-based optimal estimation of transitional and turbulent flows

Abstract: We extend the resolvent-based estimation approach recently introduced by Towne etal. (J. Fluid Mech., vol. 883, 2020, A17) to obtain optimal, non-causal estimates of time-varying flow quantities from low-rank measurements. We derive optimal transfer functions between the measurements and certain nonlinear terms that act as a forcing on the linearised Navier–Stokes equations, and show that the resulting transfer function to the flow state is equivalent to a multiple-input, multiple-output Wiener filter if the colour of the forcing statistics is known. A matrix-free implementation is developed based on integration of the direct and adjoint linearised Navier–Stokes operators, enabling application to the large systems encountered for transitional and turbulent flows without the need for a priori model reduction. Using a linearised Ginzburg–Landau problem, we show that the non-casual resolvent-based method outperforms a casual Kalman filter for general sensor configurations and recovers the Kalman filter transfer function in specific cases, leading to causal estimates at a significantly reduced computational cost. Additionally, our method is shown to be more accurate and robust than popular approaches based on truncation of the resolvent operator to its leading modes. The applicability of the method to transitional and turbulent flows is demonstrated via application to a (linearised) transitional boundary layer and a (nonlinear) turbulent channel flow. Errors on the order of 2 % are achieved for the boundary layer, and the channel flow case highlights the need to account for the forcing colour to achieve accurate flow estimates. In practice, our method can be used as a post-processing tool to reconstruct unmeasured quantities from limited experimental data, and, in cases where the transfer function can be accurately truncated to its causal components, as a low-cost estimator for flow control.

Effect of array submergence on flow and coherent structures through and around a circular array of rigid vertical cylinders

Abstract: Flow past a submerged array of rigid cylinders is more complex compared to the limiting case of an emerged array because part of the flow approaching the array is advected over it and the mean-flow three-dimensionality is increased inside and around the array. For sufficiently high submergence, the flow moving over the top of the array generates a vertical separated shear layer (SSL) and modifies the structure of the wake flow. The case of a circular array of diameter D containing solid cylinders of diameter d (=0.03D) and height hp placed in a flat-bed open channel of depth h = 0.56D is investigated. Detached eddy simulations that resolve the flow past the individual cylinders are conducted at a Reynolds number ReD = 37 500 for two solid volume fractions (SVF) of the array region (SVF = Nd2/D2 = 0.09 and SVF = 0.23 corresponding to aD = 3.9 and 9.6, where N is the number of cylinders in the array and aD is the nondimensional frontal area per unit volume for the array) and several values of the relative height of the cylinders (hp/h = 0.25, 0.5, 0.75, and 1). Results are also compared with the limiting case of a solid cylinder (SVF = 1). The strong weakening of the antisymmetric vortex-shedding mode observed for submerged cases with hp/h ≤ 0.75 is related to the flow component advected over the array and the formation of a U-shaped vortex behind the array, which impedes the interactions of the two lateral (horizontal) SSLs forming on the sides of the array. For sufficiently high SVFs and high array submergence, the U-shaped vortex penetrates inside the array, which means that fluid and particles from the near wake can enter the array region. The decrease in hp/h reduces the coherence of the horseshoe vortex forming in front of the array, the length of the steady wake region, and the Strouhal number associated with the antisymmetric shedding mode. Simulation results show that billow vortices have a much reduced capacity to entrain and carry sediments in the wake of the array even for relatively low array submergences (e.g., for hp/h = 0.75) compared to hp/h = 1. The decrease in the mean streamwise drag coefficient for the cylinders in the array, C¯d, with the decrease in hp/h, is nearly linear for hp/h > 0.25. The rate of decay of C¯d with the decrease in hp/h increases with the SVF. Using the simulation results, the paper also discusses how changes in the flow structure triggered by increased array submergence affect nutrient and sediment transport inside and around vegetated patches in natural erodible channels.

Self-sustained elastoinertial Tollmien─Schlichting waves

Abstract: Direct simulations of two-dimensional plane channel flow of a viscoelastic fluid at Reynolds number at which the nonlinear solution family comes into existence is just above this transition. Finally, evidence indicates that this branch is connected through an unstable solution branch to two-dimensional elastoinertial turbulence (EIT). These results suggest that, in the parameter range considered here, the bypass transition leading to EIT is mediated by nonlinear amplification and self-sustenance of perturbations that excite the TS mode.

Attached eddy model revisited using a minimal quasi-linear approximation

Abstract: Townsend’s model of attached eddies for boundary layers is revisited within a quasi-linear approximation. The velocity field is decomposed into a mean profile and fluctuations. While the mean is obtained from the nonlinear equations, the fluctuations are modelled by replacing the nonlinear self-interaction terms with an eddy-viscosity-based turbulent diffusion and stochastic forcing. Under this particular approximation, the resulting fluctuation equations remain linear, enabling solutions to be superposed, the same theoretical idea used in the original attached eddy model. By leveraging this feature, the stochastic forcing is determined self-consistently by solving an optimisation problem which minimises the difference between the Reynolds shear stresses from the mean and fluctuation equations, subject to a constraint that the averaged Reynolds shear-stress spectrum is sufficiently smooth in the spatial wavenumber space. The proposed quasi-linear approximation is subsequently applied to channel flow for Reynolds number , and the supporting evidence is presented using the existing DNS data.

On the scaling of large-scale structures in smooth-bed turbulent open-channel flows

Abstract: This paper investigates the existence and scaling of the so-called large-scale and very-large-scale motions (LSMs and VLSMs) in non-uniform turbulent open-channel flows developing over a smooth bed in a laboratory flume. A laser Doppler anemometry system was employed to measure vertical profiles of longitudinal and bed-normal velocity statistics over a wide range of hydraulic conditions. Pre-multiplied spectra of the longitudinal velocity fluctuations revealed the existence of two peaks occurring at wavelengths consistent with those associated with LSMs and VLSMs as detected in the past literature pertaining to wall turbulence. However, contrary to so-called canonical wall flows (i.e. flat-plate boundary layers, pipe and closed-channel flows), the LSM and VLSM peaks observed in the open-channel flows investigated herein are detectable over a much larger extent of the wall-normal coordinate. Furthermore, the VLSM peak appears at von Karman numbers $Re_{\unicode[STIX]{x1D70F}}$ as low as 725, whereas in other wall flows much higher values are normally required. Finally, as conjectured by a recent study on uniform rough-bed open-channel flows, the present paper confirms that LSM wavelengths scale nicely with the flow depth, whereas the channel aspect ratio (i.e. the ratio between channel width and flow depth) is the non-dimensional parameter controlling the scaling of VLSM wavelengths. The intensity and wavelengths of the VLSM peaks were also observed to depend on the spanwise coordinate. This result suggests that VLSMs might be dynamically linked to secondary currents, as these are also known to vary in strength and size across the channel width.

A first coherent structure in elasto-inertial turbulence

Abstract: Two dimensional channel flow simulations of FENE-P fluid in the elasto-inertial turbulence regime reveal distinct regimes ranging from chaos to a steady travelling wave which takes the form of an arrowhead structure. This coherent structure provides new insights in the polymer/flow interactions driving EIT, which are observed in a set of controlled numerical experiments and the study of transfer between elastic and turbulent kinetic energy.

Two-point stress-strain rate correlation structure and non-local eddy viscosity in turbulent flows

Abstract: By analyzing the Karman-Howarth equation for filtered velocity fields in turbulent flows, we show that the two-point correlation between filtered strain-rate and subfilter stress tensors plays a central role in the evolution of filtered-velocity correlation functions. Two-point correlations-based {\it statistical priori tests} thus enable rigorous and physically meaningful studies of turbulence models. Using data from direct numerical simulations of isotropic and channel flow turbulence we show that local eddy viscosity models fail to exhibit the long tails observed in the real subfilter stress-strain rate correlation functions. Stronger non-local correlations may be achieved by defining the eddy-viscosity model based on fractional gradients of order $0<\alpha<1$ rather than the classical gradient corresponding to $\alpha=1$. Analyses of such correlation functions are presented for various orders of the fractional gradient operators. It is found that in isotropic turbulence fractional derivative order $\alpha \sim 0.5$ yields best results, while for channel flow $\alpha \sim 0.2$ yields better results for the correlations in the streamwise direction, even well into the core channel region. In the spanwise direction, channel flow results show significantly more local interactions. The overall results confirm strong non-locality in the interactions between subfilter stresses and resolved-scale fluid deformation rates, but with non-trivial directional dependencies in non-isotropic flows.

Peristaltic channel flow and heat transfer of Carreau magneto hybrid nanofluid in the presence of homogeneous/heterogeneous reactions.

Abstract: The purpose of present work is to explore the features of homogeneous–heterogeneous reactions in peristalsis flow of Carreau magneto hybrid nanofluid with copper and silver nanoparticles in a symmetric channel. The velocity slip condition and thermal radiation effect is also taken in the simplified model. Thermodynamic optimization aspect is discussed through the entropy generation analysis. The proposed mathematical systems are modified by using a lubrication approach and solved by a homotopy-based package-BVPh 2.0. The impacts of different involved parameters on flow characteristics, thermal characteristics, chemically reactive concentration and entropy generation are scrutinized through analytic results. It reveals that the fluid velocity decreases with the increasing values of the Weissenberg and the Hartman numbers. Characteristics of the Brinkman and the thermal radiation numbers are quite reverse for the heat transfer rate. In addition, entropy generation decreases with thermal radiation and Weissenberg number. The main outcome signifies that hybrid nanofluid is better thermal conductor as compared to the conventional nanofluid.

Testing a theoretical resistance law for overland flow under simulated rainfall with different types of vegetation

Abstract: In this paper a recently theoretically deduced flow resistance equation, based on a power-velocity profile, was tested using data collected for overland flow under simulated rainfall carried out in plots with vegetation. The available data were obtained exploring a wide range of rainfall intensities (from 60 to 181 mm h−1) and slopes (from 3.6 to 39.6%), and with four different types of vegetation. The database, including measurements of flow velocity, water depth, cross sectional flow area, wetted perimeter and bed slope, was divided in four datasets (one for each vegetation type), which allowed the calibration of the relationship between the velocity profile parameter Γ, the slope steepness, the flow Froude number, and the rainfall Reynolds number. The effect of rainfall intensity and different types of vegetation on flow resistance was investigated. The results showed that the theoretically deduced flow resistance equation allowed an accurate estimate of the Darcy-Weisbach friction factor for overland flow under simulated rainfall and in presence of vegetation. The developed analysis also suggested that flow resistance increases with rainfall intensity for laminar overland flow. The available data demonstrated that a quasi-independence between slope and mean velocity occurred. Finally, a single flow resistance equation resulted applicable to all investigated vegetation types and this equation was affected by flow regime represented by flow Reynolds number.

The growth mechanism of turbulent bands in channel flow at low Reynolds numbers

Abstract: In this work, we carried out direct numerical simulations in large channel domains and studied the kinematics and dynamics of fully localised turbulent bands at Reynolds number . Our results show that the downstream end of the band features fast streak generation and travels into the adjacent laminar flow, whereas streaks at the upstream end decay continually and more slowly. This asymmetry is responsible for the transverse growth of the band. We particularly investigated the mechanism of streak generation at the downstream end, which drives the growth of the band. We identified a spanwise inflectional instability associated with the local mean flow near the downstream end, and our results strongly suggest that this instability is responsible for the streak generation and ultimately for the growth of the band. Based on our study, we propose a possible self-sustaining mechanism of fully localised turbulent bands at low Reynolds numbers in channel flow.

Performance comparison of four turbulence models for modeling of secondary flow cells in simple trapezoidal channels

Abstract: Due to the importance of channel flow characteristics in the water conveyance, the study of it is a noteworthy problem for hydraulics experts and much attempts has been accomplished for the modelin...

Lift and drag force on a spherical particle in a viscoelastic shear flow

Abstract: We present a comprehensive 3D numerical study of particles with imposed velocities relative to the local bulk flow (termed “slip velocities”) in a viscoelastic shear flow. We consider the force on a spherical particle sedimenting, a spherical bubble rising, and a spherical neutral squirmer swimming in an imposed viscoelastic shear flow. We demonstrate that any particle moving with a slip velocity in the flow or gradient direction of the shear flow experience a lateral lift force. We calculate and compare the magnitude and direction of the lift force in all situations. At small Deborah (De) and Weissenberg (Wi) numbers, our results show good agreement with an existing perturbation theory for rigid particles (Einarsson and Mehlig, 2017 [1]) and new perturbation theories for drops and for squirmers respectively. Our simulations extend these results to higher De and Wi regimes. Through our simulations, we uncover the physical mechanism of the lateral force on all particles. For rigid particles, we find the lift force arises from an imbalance in polymer stress on either side of the particle, which in turn is due to the imbalance of polymer stretch surrounding the particle. If this lift force is not balanced by an external force, a lateral drift velocity arises. We further consider the implication of this lateral drift for rigid particles hydrodynamically forced in a viscoelastic Poiseuille flow, where particles can migrate either toward the channel center plane or toward the wall, depending on whether the direction of the applied force is in the direction aligned or opposite to the direction of the Poiseuille flow, respectively. We study both the migration of a single particle as well as a suspension of particles in channel flow. Even with the addition of hydrodynamic interactions, we show that particles forced in the direction of the Poiseuille flow migrate towards the channel center.

Stability condition of self-organizing staggered particle trains in channel flow

Abstract: The inertial focusing of particles in channel flow of a Newtonian fluid is studied using the lattice Boltzmann method. The effects of Reynolds number (Re) and blockage ratio (k) on the stability condition of self-organizing staggered particle trains are explored. The results show that, for staggered particle pairs, the particles will move close to each other with a damped oscillatory trajectory and form a steady horizontal spacing eventually. For single-line particle pairs, the inter-particle spacing increases continuously to a larger value for further downstream. Two lines of 12 particles will self-organize the staggered particle trains. The formation of stable staggered particle trains is dependent on Re and k. Particles with low k in the staggered particle trains are more likely to be unstable or fluctuate within a certain range when Re is larger than a critical value. As k increases, the critical values of Re corresponding to the inter-particle spacing with a stable value or a certain range of fluctuation are also increased. The mean particle spacing decreases with increasing k and decreasing Re, and the blockage ratio k has a greater effect on the particle spacing than Reynolds number Re.

Assessment of pseudo-plastic and dilatant materials flow in channel driven cavity: application of metallurgical processes

Abstract: Non-Newtonian fluid rheology representing the properties of pseudoplastic and dilatant materials has received overwhelming attention due to extensive applications in industrial and technological sectors like in metallurgical processes, shock absorbing materials, smart structures, and devices with adaptive stiffness, damping, emulsions, suspensions and so forth. Thus, in current communication characteristics of power law fluid elucidating attributes of pseudoplastic and dilatant materials in channel driven cavity is addressed. Finite element method (FEM) is implemented to interpret rheological features of power law fluid by varying flow controlling parameters. Discretization of domain at coarse level is performed by using stable first and second order polynomial (P2−P1) shape functions. Square shaped cylinder is placed at (1, 1.5) above the cavity. Hydrodynamics forces like pressure difference drag and lift variations are measured at outer surface of cylinder. The impact of primitive parameters like power law index (n) and Reynold number on velocity, pressure and viscosity for shear thinning and thickening cases is adorned. It is deduced that pressure difference increased against the variation in power law index. In similar way the impact of drag and lift forces mounts by increasing power law index. Reynold number has delineating impact on drag and lift forces near the obstacle. It is also seen that pressure shows optimized non-linear behavior near the obstacle and becomes linear along the downstream as expected in channel flow. It is divulged that pressure drops more rapidly for increasing magnitude of Reynold number. Velocity of fluid increases when power law fluid flow is behaving as shear thinning fluid in comparison to shear thickening case.

A Review on Hydrodynamics of Free Surface Flows in Emergent Vegetated Channels

Abstract: This review paper addresses the structure of the mean flow and key turbulence quantities in free-surface flows with emergent vegetation. Emergent vegetation in open channel flow affects turbulence, flow patterns, flow resistance, sediment transport, and morphological changes. The last 15 years have witnessed significant advances in field, laboratory, and numerical investigations of turbulent flows within reaches of different types of emergent vegetation, such as rigid stems, flexible stems, with foliage or without foliage, and combinations of these. The influence of stem diameter, volume fraction, frontal area of stems, staggered and non-staggered arrangements of stems, and arrangement of stems in patches on mean flow and turbulence has been quantified in different research contexts using different instrumentation and numerical strategies. In this paper, a summary of key findings on emergent vegetation flows is offered, with particular emphasis on: (1) vertical structure of flow field, (2) velocity distribution, 2nd order moments, and distribution of turbulent kinetic energy (TKE) in horizontal plane, (3) horizontal structures which includes wake and shear flows and, (4) drag effect of emergent vegetation on the flow. It can be concluded that the drag coefficient of an emergent vegetation patch is proportional to the solid volume fraction and average drag of an individual vegetation stem is a linear function of the stem Reynolds number. The distribution of TKE in a horizontal plane demonstrates that the production of TKE is mostly associated with vortex shedding from individual stems. Production and dissipation of TKE are not in equilibrium, resulting in strong fluxes of TKE directed outward the near wake of each stem. In addition to Kelvin–Helmholtz and von Karman vortices, the ejections and sweeps have profound influence on sediment dynamics in the emergent vegetated flows.