Flow Drag Force Research Articles

Experimental investigation on the characteristics of seepage failure of landslide dams with strongly permeable zones

Landslide dams are formed by river blockages caused by landslides or other slope instability bodies. They exhibit loose structure, poor stability and strong permeability. Large water head caused by water-level increase can trigger seepage deformation of soil and influence the stability of landslide dams, possibly leading to dam breach and catastrophic damage. Various landslide dam structures also result in differences in seepage characteristics. In this study, multiple physical model tests for seepage failure of landslide dams with strongly permeable zones were designed. The influence of the location and gradation of the strongly permeable zones on the seepage of landslide dams was studied. The characteristics and modes of seepage failure of landslide dams with strongly permeable zones were analysed. The experimental results showed that the cyclic evolution failure of piping and downstream slope collapse was an essential failure mode for the seepage-induced failure of landslide dams with strongly permeable zones. Compared with the strongly permeable zone at the bottom of a landslide dam, the piping caused by seepage evidently promoted the slope erosion of the dam with the strongly permeable zone in the middle. As the permeability coefficient of strongly permeable zones increased, piping was faster and easier to form, and piping failure, slope erosion, and slope collapse were more severe. The seepage failure of landslide dams mainly included the emergence of seepage water, piping, slope erosion, and downstream slope collapse. Piping was caused by the erosion and migration of some fine particles of soil in seepage channels in the dam. When the flow drag force could overcome the resistance force among the soil particles, some fine particles and even large particles on the downstream slope surface were continuously eroded. This study provides new insights into the evolution process and breach mechanisms for the seepage-induced failure of landslide dams with strongly permeable zones.

Flow across a circular cylinder in an inclined channel stabilized by buoyancy

In this study, flow across a circular cylinder confined in an inclined channel is considered, with account taken of mixed convection. Cases with opposing or aiding buoyancy that is not in alignment with the incoming flow are considered, and it is found that the flow around and in the wake of the cylinder is affected. The effects of inclination and buoyancy on the flow and heat transfer patterns are investigated, with a focus on the stabilization and destabilization of flow by these two factors. Simulation results are analyzed with regard to the flow field, lift and drag forces, heat transfer, the deviation of separation and through-flow in the channel, and the temperatures on the channel walls. The flow is more strongly destabilized by an opposing buoyancy, but can be fully stabilized by an aiding buoyancy in an inclined channel. The drag on the cylinder is minimized around a critical Richardson number Ricr. The inclination of the channel has significant effects on the local heat transfer on the cylinder and on the characteristics of the through-flow. The pattern of the wake flow, i.e., whether it is steady or unsteady, affects the heating of the channel walls.

Free-surface channel flow around a square cylinder

The free-surface channel flow around a square cylinder is analysed, over a wide range of blocking ratios, using three-dimensional simulations. The state of the flow is characterised in terms of the Froude number upstream and downstream of the square cylinder. The simulations confirm the presence of the subcritical and choked states, and provide new insight into the supercritical state and band-gap through an analysis of how the momentum flux varies with Froude number along the channel. The influence of the blocking ratio on the flow state and drag force is analysed and shows the significant rise of drag in the choked regime.

Decomposition of the drag force in steady and oscillatory flow through a hexagonal sphere pack

We investigate steady and oscillatory flow through a hexagonal close-packed arrangement of spheres in the framework of the volume-averaged momentum equation. We quantify the friction and pressure drag based on a direct numerical simulation dataset. Using the pressure decomposition of Graham (J. Fluid Mech., vol. 881, 2019), the pressure drag can be further split up into an accelerative, a viscous and a convective contribution. For the accelerative pressure, a closed-form expression can be given in terms of the potential flow solution. We investigate the contributions of the different drag components to the volume-averaged momentum budget and their Reynolds number scaling. For steady flow, we find that the friction and viscous pressure drag are proportional to $Re$ at low Reynolds numbers and scale with $Re^{1.4}$ for high Reynolds numbers. This is close to the steady laminar boundary layer scaling. For the convective pressure drag, we find a cubic scaling at low and a quadratic scaling at high Reynolds numbers. The Reynolds stresses have a minor contribution to the momentum budget. For oscillatory flow at low and medium Womersley numbers, the amplitudes of the drag components are similar to the steady cases at the same Reynolds number. At high Womersley numbers, the drag components behave quite differently and the friction and viscous pressure drag are relatively insignificant. The drag components are not in phase with the forcing and the superficial velocity; the phase lag increases with the Womersley number. This suggests that new models beyond the current quasisteady approaches need to be developed.

Nonlinear dynamics of novel flight-style autonomous underwater vehicle with bow wings, Part I: ASE and CFD based estimations of hydrodynamic coefficients, Part II: Nonlinear dynamic modeling and experimental validations

Accurate dynamic modeling is essential for precise prediction of six degrees-of-freedom (6-DOF) motion and model-based controller design of an autonomous underwater vehicle (AUV). The accuracy of dynamic model of an AUV largely depends upon the precise estimation of hydrodynamic coefficients. Accordingly, to establish the dynamic model based on ASE-estimated hydrodynamic coefficients of the novel flight-style AUV and experimental validations, the study is presented in two parts (Part I: ASE and CFD based estimations of hydrodynamic coefficients and Part II: Nonlinear dynamic modeling and experimental validations).Part I: In this part complete set of nonlinear hydrodynamic coefficients including, added mass, drag, and lift forces and moment coefficients are estimated using ASE technique, which is specifically developed to accurately comprehend the novel AUV design including, AUV hull, fixed wings, control fins, and appendages. Additionally, an improved ASE approach is also proposed to estimate cross flow drag force coefficients. In proposed improved ASE technique, (Cdc) in mathematical formulation is taken from the experimental results of 3D flow past over circular cylinder instead of 2D, as followed previously to estimate the nonlinear cross-flow drag force and moment coefficients (Yvv,Zww,Mww,Nvv,Yrr,Zqq,Mqq&Nrr). The proposed ASE technique is verified and validated in two stages: first, by comparing the ASE-estimated results with CFD-based estimations, and second, by investigating the 6-DOF motion response of the AUV. When compared ASE-estimations with the CFD results for the cross-flow drag force and moment coefficients, the proposed ASE technique has shown a significant improvement (approximately 20%) over the previously employed ASE method. The ASE-estimated results are validated through 6-DOF motion response of AUV during free-running underwater experiments, provided in ‘Part II’. Overall, the proposed ASE technique is considered more effective, direct, and less costly in terms of time and computational efforts, compared to CFD-based or experimental-based estimations of hydrodynamic coefficients of AUVs, particularly torpedo-shaped AUVs.Part II: This part presents a nonlinear dynamic model for a newly designed torpedo-shaped flight-style AUV having complex bow and stern fixed wings and control fins configuration. The model includes precise mathematical formulations to accurately represent the physics of the AUV and underwater environment in terms of hydrodynamic derivatives such as added mass, drag, and lift forces and moment coefficients. These coefficients have been estimated using an ASE method provided in ‘Part I’. The 6-DOF motion response of the AUV has been simulated in both horizontal and vertical planes which includes, zigzag yaw, circle, zigzag pitch, and spiral maneuvers. The lift generated by the bow and stern control fins has been investigated both separately and collectively, especially during complex spiral ascending maneuvers. Moreover, improved ASE technique for cross flow drag coefficients has also been validated through 6-DOF free-running underwater experiments of AUV and insights on impact of cross flow drag coefficients on 6-DOF motion response of AUV has also been provided. Overall, the comparison between the simulated AUV motion and free-running underwater experiments demonstrated consistency, thereby validating the accuracy of the nonlinear dynamic modeling, ASE-based hydrodynamic coefficient predictions, and effectiveness of the newly designed flight-style AUV for underwater operations.

Heat and Mass Transfer On MHD Flow Problems with Hall and Ion Slip Effects On Exponentially Accelerated Plate

We in this paper intended to investigate heat and mass transfer for MHD free convective flow for exponentially accelerated plate. The effects of Ion slip and Hall are studied considering variable temperatures, concentration, and angle of inclination. We applied finite element analysis for solving governing equations. Flow velocity, concentration and temperature’s graphical profiles are examined for non-dimensional parameters. Flow reversal is prevented due to magnetic field, is observed. Velocity experiences retarding effect due to angle of inclination, this helps in acknowledging drag force in seepage flow.

Numerical study of unsteady tangent hyperbolic fuzzy hybrid nanofluid over an exponentially stretching surface

The significance of fuzzy volume percentage on the unsteady flow of MHD tangent hyperbolic fuzzy hybrid nanofluid towards an exponentially stretched surface is scrutinized. The heat transport mechanism is classified by Joule heating, nonlinear thermal radiation, boundary slippage, and convective circumstances. Ethylene glycol (EG) as a host fluid along with the nanomaterial’s Cu and {text{Al}}_{{2}} {text{O}}_{{3}} are used for heat transfer analysis is also considered in this investigation. The nonlinear governing PDEs are meant to be converted into ODEs employing appropriate renovations. Then, a built-in MATLAB program bvp4c is employed to acquire the outcome of the given problem. The variation of flow rate, thermal heat, drag force and Nusselt number and their influence on fluid flow with heat transfer have been scrutinized through graphs. An increase in thermal radiation, power law index and nanoparticle volume friction heightens the heat transmission rate. Skin friction is diminished by swelling the power-law index, Weissenberg number, and ratio parameters, whereas it is increased by enhancing the magnetic parameter. The heat transfer rate upsurges with an increase in Weissenberg number and nanoparticle volume fraction. Also, the nanoparticle volume percentage is expressed as a triangular fuzzy number (TFN). The triangular membership function (MF) and TFN are regulated by the chi - {text{cut}} parameter, which has a range of 0 to 1. In comparison to nanofluids, hybrid nanofluids have a higher heat transmission rate, according to the fuzzy analysis. This investigation has applications in the areas of paper manufacturing, metal sheet cooling and crystal growth.

Application of PIV for Virtual Mass Coefficient Measurement

The particle image velocimetry (PIV) technique is employed for the measurement of the virtual mass of a submerged object, an important parameter in the two-fluid model, particularly so for reactor thermal-hydraulic and safety analyses. Instead of carrying out the measurement through traditional transient processes that mix steady-state drag, virtual mass force, and Basset force, a new PIV approach is developed for steady-state flows through the integration of the fluid kinetic energy around the object. The Basset force, an inseparable transient force in viscous flows, is eliminated in the new approach, making virtual mass quantification possible. This new method has been applied to the virtual mass measurement of a solid cylinder, and although the measurement uncertainty from the flow’s random fluctuations is substantial, the results are very encouraging. The results suggest that the existence of drag force in viscous flow affects the virtual mass, as the flow field is different from the ideal potential flow. When the measurement method was applied to the quantification of air bubbles, no reliable data were obtained due to complications from bubble lateral motions and deformation. Further study is needed for the PIV method to be employed for bubble virtual mass force measurements under steady-state flow conditions.

Large eddy simulation of supersonic flow in ducts with complex cross-sections

Large Eddy Simulation (LES) has been employed for the investigation of supersonic flow characteristics in five ducts with varying cross-sectional geometries. The numerical results reveal that flow channel configurations exert a considerable influence on the mainstream flow and the near-wall flow behavior. In contrast to straight ducts, square-to-circular and rectangular-to-circular ducts exhibit thicker boundary layers and a greater presence of vortex structures. Given the same inlet area, rectangular-to-circular ducts lead to higher flow drag force and total pressure loss than square-to-circular ducts. Characterized by the substantial flow separation and shock waves, the “S-shaped duct shows significant vertically-asymmetric characteristics.

EXPLORING THE DYNAMICS OF AN EXOTHERMIC CHEMICAL REACTION CONTROLLED BY ARRHENIUS KINETICS WITH HALL EFFECT IN A MICROCHANNEL

The consequences of chemically reactive fluids have provoked many researchers due to their potential to enhance the behavior of heat. Hence, this article discussed a theoretical investigation to explore the actions of Arrhenius chemical reaction and Hall current on hydro-magnetic free convection of a viscous fluid flowing along an upstanding micro-channel. Subject to the required boundary conditions, the governing coupled equations representing the flow pattern in non-dimensional form were solved using the homotopy perturbation method (HPM). Line graphs are also used to generate expressions for energy, momentum, volume flow rate, drag force, and Nusselt number in both primary and secondary flow directions as a function of regulating parameters like chemical reaction, Hall current, rarefaction, and wall ambient temperature difference ratio. It is worthy of note that the fluid temperature and the fluid flow are substantially propelled by the viscous heating term in the Arrhenius chemical reaction of the system for growing values of the wall ambient temperature difference ratio parameter. Additionally, it is noticeable that volume flow rate performance is seen as a growing influence of viscous heating and rarefaction parameters. The findings of this study can be applied to a wide range of electrically controlled devices, thermal and petro chemical engineering, and the serviceability of industrial products.

Power Elliptic Bodies of Minimum Resistance in the Gas Flow

For power elliptical body, the drag force in the high-speed rarefied gas flow is calculated based on several local models. The solution of the variational problem determines the degree of minimum resistance in the generatrix of the body, depending on coefficient of the ellipticity and different elongation in a wide range of Reynolds numbers.

Transient simulation of melt flow, clogging, and clog fragmentation inside SEN during steel continuous casting

Clogging of submerged entry nozzle (SEN) during continuous casting of steel is an undesirable phenomenon leading to different problems like flow blockage, slag entrainment, nonuniform solidification, etc. A transient numerical model for nozzle clogging based on an Eulerian-Lagrangian approach was developed and it covers the main steps of clogging: (a) formation of the first oxide layer by chemical reactions on the steel-refractory interface; (b) motion of non-metallic inclusions (NMIs) due to the turbulent melt flow towards the SEN wall; (c) interactions between the melt, the NMI, and the wall; (d) formation and growth of the clog by the deposition of NMIs on the clog front and the flow-clog interactions; and (e) detachment/fragmentation of a part of clog due to the flow drag force. Clogging in an industrial scale SEN was simulated. The simulated clog front was compared with real as-clogged SENs. The modeling results have successfully explained the SEN clogging induced transient flow phenomenon in the mold region, i.e. the transition from the stable to an unstable and non-symmetrical flow.

Thin film flow of the ternary hybrid nanofluid over a rotating disk under the influence of magnetic field due to nonlinear convection

This study focuses on the comprehensive analysis of thermal characterization of the ternary hybrid nanofluid flow within a continuously extending disk. The characteristics of time-dependent magnetohydrodynamics tri-hybrid nanofluids consisting Molybdenum disulfide (MoS2), Silicon dioxide (SiO2), Multi-Walled Carbon Nanotubes (MWCNT), Water (H2O), hybrid (MWCNT + MoS2/H2O) and nanofluid (MWCNT/H2O) movement are analyzed for the thermal applications. With the help of ohmic heating, quadratic convection, and a magnetic field the heat transmission mechanism and fluid dynamics are investigated.The significance of the study describe that tri-hybrid nanofluid has a higher energy transport rate than the traditional fluid at the surface of the disk.The transformed coupled and nonlinear ordinary differential equations are solved analytically using Homotopy Analysis Method (HAM). The impact of some important physical parameters on the fluid flow profile, temperature fields, drag force, and rate of heat transmission is depicted using plots. The outcomes are validated by previous studies and a good degree of consistency is revealed.

Antithrombotic and Flow Drag‐Reducing Material for Blood‐Contacting Medical Devices

AbstractBlood‐contacting medical devices are often associated with shear‐induced and contact activation thrombosis. Superhydrophobic materials have shown promise to reduce flow drag forces, but not contact activation. Here, a strategy of selectively grafting a potent anti‐thrombin compound on the tips of the surface microstructures of a superhydrophobic polytetrafluoroethylene foam, is presented, to concurrently achieve drag reduction and anti‐thrombosis. This work shows that two grafting approaches – Argon plasma or piranha solution treatment – followed by covalent cross‐linking can successfully graft the drug to the outer tips of the foam and provide anti‐thrombotic functionality. By avoiding grafting to the inner regions of the foam, the surface's drag reduction properties can be retained. The functional durability of the grafted surfaces is evaluated by strong water jetting, which demonstrates that the plasma approach can withstand substantial fluid shearing but not the piranha approach, although the plasma approach involves stronger compromise to the drag reduction capabilities. As the proposed selective grafting strategy is applied to a bulk foam, it can be complemented with a previously proposed strategy of supplying air pressure to the foam pores to bolster resistance to fluid impalement and plastron dissolution, allowing the material to be used in medical devices with high fluid pressures.

Optimization of air inlet features of an active indirect mode solar dryer: A response surface approach

The effect of air flowing into an in an active indirect mode solar dryer was studied. The study aimed at optimizing the airflow features of a solar dryer of active indirect feature using Response Surface Methodology (RSM). The factors of the experiment included the product slice thickness of the experimental product and the air vent of the dryer. The two factors were considered at five levels and a total of 13 experimental runs derived. The air vent was based on the following shape orientations: square, rectangular, circular, and triangular. The thickness of the product was considered at five levels of 4, 8, 12, 16 and 20 mm. The responses from the experimental set up were the air flow rate and drag force, which were determined using established equations. The optimum values for the air flow rate and drag force were 0.0275 m3/s and 0.0476N, respectively. The corresponding optimal conditions which gave the optimum responses were 100 cm2 - square inlet and product slice thickness of 20 mm for air flow rate and 80 cm2 -rectangular inlet and product slice thickness of 20 mm for drag force, respectively. The models for predicting the responses were adequate, with r-square values 0.9463 and 0.9376 and desirabilities of 99.2 and 95.0% for air flow rate and drag force respectively. The experiment was repeated using the optimal conditions to validate the optimum responses. The variation between the predicted and experimental data was less than 8%.

Winglets effect on the aerodynamics of aircraft wing; computational studies

Aircraft drag reduction has been of interest to aerospace industry for long time. Therefore, in the past decade different flow control techniques have been used such as active and passive flow control techniques. Winglet design has been explored in the past both experimentally and computationally. Experimental studies pose significant challenges due to the wing-span and costly equipment and facilities. Therefore, this study concerns the computational studies of winglet design using the large-eddy simulation approach. The results show that the winglet design reduces the flow separation and drag force, while the pressure and lift force increases.

Numerical study on the effect of airflow on powder mixing in a container blender

Powder mixing is critical in many industries. Despite the wide variety of available mixers, the container blender is favored in industries due to easy manufacturing and convenient operation. As fine powders are frequently encountered in practical mixing, the presence of air during mixing may significantly impact the process. However, a scientific understanding of air–particle interactions in powder mixing has not been established so far. From a physical view, the air drag force on particles might be significant when the gas velocity is high and the particles are fine. Therefore, this novel study numerically investigates the effects of particle size and air presence on powder mixing under typical conditions, such that the relationship between particle–fluid dynamics and mixing performance is clarified for the first time. In the calculation, our advanced computational fluid dynamics–discrete element method, namely, the flexible Eulerian–Lagrangian method with an implicit algorithm, is utilized. To examine the effect of particle size on powder mixing, the coarse-grained discrete element method is employed for fine particle systems. Through the advanced numerical framework, the effect of airflow on powder mixing can be discussed in depth. The numerical results show that airflow accelerates the mixing of fine particles under the investigated rotation speeds. Based on the calculation results of the particle kinetics and fluid velocity distribution, it is clarified that the accelerated mixing results from the fine particle movement under air entrainment. How the movement of fine particles is developed is also elucidated by the continuously circulating gas flow and fluid drag force. Thus, this study provides a new understanding of the effects of airflow on powder mixing, which has not been scientifically clarified in previous studies.

Flow drag force contributes high bio-treatment efficiency in a circulating fluidized bed reactor: Mechanism of selective separation of functional decayed sludge

The diversity and expression of microbial function of activated sludge are influenced by combined effect of environmental factors and selective separation. The selective separation of sludge greatly depends on the design of reactor. The discharge of decayed microorganisms and the retain of active microorganisms cannot be realized through sedimentation and reflux of the activated sludge in the conventional secondary sedimentation tank. Thus, this study proposed a strategy for in-situ selective separation of activated sludge by means of the circulating flow field. The fluid field in the fluidized bed reactor was found to influence the distribution of activated sludge with different physical properties, biological properties, and functions. The sludge with various particle sizes showed different bio-characteristics. Then, based on the cumulative distribution of mean floc size, three kinds of component sludge with different floc sizes (sludge-a: 10.56–81.42 μm, 28.3 %; sludge-b: 81.42–104.63 μm, 26.1 %; and sludge-c: 104.63–257.94 μm, 45.6 %) were hypothesized to constitute all the sludge in the fluidized bed reactor for simplification of heterogeneous sludge. Finally, computational fluid dynamical and simulation calculations were used to reveal the impact of selective sludge discharge on bio-treatment efficiency. The results indicated that the bio-treatment efficiency could be improved by more than 5.0 % based on the selective discharge of decayed sludge with the same input of energy. This work demonstrated a principle that a fluid field could be used to identify functionally decayed sludge in a fluidized bed reactor for wastewater treatment. The principle could play an important role in identification and separation of microbial function decayed sludge for improving the bio-reaction efficiency, energy utilization rate and stability of reactor.

Local Scour Mechanism of Offshore Wind Power Pile Foundation Based on CFD-DEM

The local scour around offshore pile foundations often seriously affects the normal operation of offshore wind power. The most widely used numerical simulation method in the study of local scour is the Euler two-fluid model (TFM). However, the contact effect between sediment particles is neglected in this model. Thus, the momentum and energy transfer between sediment particles and the fluid is not realistically reflected, which limits its significance in revealing the mesoscopic mechanism of local scour. Therefore, the computational fluid dynamics-discrete element method (CFD-DEM) numerical model was applied in this study, which fully considers the contact between solid particles and momentum transfer between two phases. The model was first verified by experimental data of a local scour test under clear water scour. Then, the mechanism of local scour was further discussed from macro and micro perspectives. The results showed that CFD-DEM could be effectively used to study the local scour around a pile foundation. The local scour was comprehensively affected by flow velocity, gravity, fluid force, drag force, and interaction between particles, etc. Although the maximum average drag force happened in the area about 90° from the direction of incoming flow, the maximum scour depth always occurred at about 45°. Corresponding findings and conclusions can be used for future reference when designing and protecting the offshore wind power pile.

Multiple-Streams Focusing-Based Cell Separation in High Viscoelasticity Flow.

Viscoelastic flow has been widely used in microfluidic particle separation processes, in which particles get focused on the channel center in diluted viscoelastic flow. In this paper, the transition from single-stream focusing to multiple-streams focusing (MSF) in high viscoelastic flow is observed, which is applied for cell separation processes. Particle focusing stream bifurcation is caused by the balance between elastic force and viscoelastic secondary flow drag force. The influence of cell physical properties, such as cell dimension, shape, and deformability, on the formation of multiple-streams focusing is studied in detail. Particle separation is realized utilizing different separation criteria. The size-based separation of red (RBC) and white (WBC) blood cells is demonstrated in which cells get focused in different streams based on their dimension difference. Cells with different deformabilities get stretched in the viscoelastic flow, leading to the change of focusing streams, and this property is harnessed to separate red blood cells infected with the malaria parasite, Plasmodium falciparum. The achieved results promote our understanding of particle movement in the high viscoelastic flow and enable new particle manipulation and separation processes for sample treatment in biofluids.