Исследование реакции поверхности жидкости на импульсное воздействие наклонной газовой струи при малых числах Рэйнольдса

A mathematical description of the motion of a cavity on the liquid surface under an oblique action of a gas jet is obtained using the well-known expressions for the movement of a gas bubble in a liquid. The boundary of the viscous drag force domination over the form drag force is determined. The impingement of the gas jet on the liquid surface is considered as a dynamic object of the automatic control theory. It is found that the dynamic properties of the two-phase system "gas jet - liquid" are described by the integrator equations. Using a specially designed setup, the transient response of the "gas jet - liquid" system were experimentally obtained for the aerodynamic action at angles of 20º and 50º to the surfaces of liquids with the viscosities of 0.71 and 26.1 Pa•s (Reynolds number Re < 2). The research results are necessary for the analysis of the non-contact aerodynamic method of liquid viscosity measurements.

Effect of Speed and Boot Opening on Aerodynamics, Fuel Consumption, and CO2 Emission of Minibus

Overspeeding and overloading contribute to road accidents. In developing countries, overloading is often indicated by open boot due to commercial transporters’ motivation to carry an excess load to boost revenue. Therefore, there is a need to provide measures to control or eliminate the practice of overspeeding and overloading. This study aims to conduct a parametric study to determine the effect of vehicle speed and boot opening on the aerodynamics of airflow around a typical minibus, fuel consumption, and CO2 emission, and recommend optimum boot opening. Computational Fluid Dynamics is employed using the FLUENT™ program. Results show the existence of a wavy pattern for drag coefficient, fuel consumption, and CO2 emission concerning boot opening. Furthermore, two boot opening regions exist: and . The first region exhibits low prediction error (maximum of 7.25%) and better fit of regression model to FLUENT™ data. The first region also has lower susceptibility to exhibit handling instability. Therefore, boot opening around is recommended as the optimum boot opening, to ensure minimum fuel consumption and CO2 emissions, improve handling and safety. The developed regression models could inform regulatory bodies’ formulation and implementation of policies to mitigate road accidents. Keywords—Boot Opening, CO2 emission, Fuel Consumption, Pressure drag, Total Drag, Minibus, Viscous Drag

Evaluating Phase Blockages and Mobility Changes During Pressure Transient Analysis

Pressure transient analysis (PTA) is a cogent methodology to evaluate dynamics of hydrocarbon reservoirs. Numerous analytical and numerical models have been developed to model various types of wellbore, reservoir, and boundary responses. However, the near-wellbore region remains to be perplexing in pressure transient analysis. In this paper we investigate the pressure transient behavior of phase blocking and mobility variations caused by fluid phase interactions or properties, such as viscous drag forces and surface tension at the near-wellbore region and their impact on pressure transient evaluation. We have used real field examples to scrutinize relative effects of mobility variations in pressure transients. The impact of capillary number (Nc) acting on the near-wellbore region and its influence on pressure transient behavior and skin alteration were examined in detail. Several real field examples honoring actual reservoir rock special core analysis (SCAL) and fluid pressure/volume/temperature (PVT) properties have been studied. Actual field data discussed in this paper for PTA were captured during drill stem testing (DST) operations from various hydrocarbon reservoirs in the Berkine Basin of Algeria. PVT laboratory-measurement-based fluid properties were used in conjunction with tuned equation of state (EOS) models to ensure consistency between wells and reservoirs. Pressure transient analysis of a gas condensate reservoir system can depict various mobility regions, especially while flowing below dew point pressure. In some cases, three-distinct-mobility regions can be identified as: a far-field zone with initial gas and condensate saturation; a mid-field zone with increased condensate saturation and lower gas relative permeability; and a near-wellbore zone with high Nc which increases gas relative permeability and mobility. These three-distinct-mobility regions form due to condensate dropping out and fluid interactions in the near wellbore. We demonstrate, with real-life field examples of the near-wellbore region, how the relative effects of viscous drag forces and surface tension forces acting across the liquid and gas interface can enable the reference fluid phase to regain its mobility. We further investigate the evaluation of skin factor in such circumstances and show how the existence of phase blocking and velocity stripping can cause over-estimation or under-estimation of skin factor. We present a novel set of real field examples and relations between various zones in hydrocarbon reservoirs to avoid snags of misleading pressure transient interpretations and how composite models can be accurately used to represent complex cases. Field examples from Algerian hydrocarbon reservoirs are depicted. The findings could be easily applied for similar reservoirs in other parts of the globe to identify and model such intricate systems.

Research on the Coupled Water–Soil SPH Algorithm Improvement and Application Based on Two-phase Mixture Theory

An improved water–soil coupling algorithm was proposed based on the two-phase mixture theory within the framework of smoothed particle hydrodynamics (SPH). In this algorithm, the buoyant density was considered in saturated soil and the stress of two phases was completely exfoliated with the Terzaghi’s effective stress principle. Then the interaction between water and soil was only constituted by viscous drag force. The proposed algorithm was validated by several numerical tests to effectively solve a series of numerical problems caused by the truncation of the kernel approximation on the interface between submerged soil and water, and it can also be a feasible measure to simulate underwater soil excavation problems without drainage and underwater landside problems. Meanwhile, combined with frictional sliding contact algorithm, the interaction between water/soil and structure which was considered as rigid can be effectively modeled, and the calculated contact forces acting on the structure are more accurate. Furthermore, this improved algorithm can be applied to deal with large deformation problems involving complex water–soil–structure interaction in hydraulic and geotechnical engineering such as underwater excavation, shield dig, caisson sinking and other practical engineering problems. It is also significant to engineering design and the improvement of construction level.

The Landslide Velocity

Proper knowledge of velocity is required in accurately determining the enormous destructive energy carried by a landslide. We present the first, simple and physics-based general analytical landslide velocity model that simultaneously incorporates the internal deformation (non-linear advection) and externally applied forces, consisting of the net driving force and the viscous resistant. From the physical point of view, the model stands as a novel class of non-linear advective – dissipative system where classical Voellmy and inviscid Burgers' equation are specifications of this general model. We show that the non-linear advection and external forcing fundamentally regulate the state of motion and deformation, which substantially enhances our understanding of the velocity of a coherently deforming landslide. Since analytical solutions provide the fastest, the most cost-effective and the best rigorous answer to the problem, we construct several new and general exact analytical solutions. These solutions cover the wider spectrum of landslide velocity and directly reduce to the mass point motion. New solutions bridge the existing gap between the negligibly deforming and geometrically massively deforming landslides through their internal deformations. This provides a novel, rapid and consistent method for efficient coupling of different types of mass transports. The mechanism of landslide advection, stretching and approaching to the steady-state has been explained. We reveal the fact that shifting, up-lifting and stretching of the velocity field stem from the forcing and non-linear advection. The intrinsic mechanism of our solution describes the fascinating breaking wave and emergence of landslide folding. This happens collectively as the solution system simultaneously introduces downslope propagation of the domain, velocity up-lift and non-linear advection. We disclose the fact that the domain translation and stretching solely depends on the net driving force, and along with advection, the viscous drag fully controls the shock wave generation, wave breaking, folding, and also the velocity magnitude. This demonstrates that landslide dynamics are architectured by advection and reigned by the system forcing. The analytically obtained velocities are close to observed values in natural events. These solutions constitute a new foundation of landslide velocity in solving technical problems. This provides the practitioners with the key information in instantly and accurately estimating the impact force that is very important in delineating hazard zones and for the mitigation of landslide hazards.

Numerical Study of Effect of Sawtooth Riblets on Low-Reynolds-Number Airfoil Flow Characteristic and Aerodynamic Performance

Riblets with an appropriate size can effectively restrain turbulent boundary layer thickness and reduce viscous drag, but the effects of riblets strongly depend on the appearance of the fabric that is to be applied and its operating conditions. In this study, in order to improve the aerodynamic performance of a low-pressure fan by using riblet technology, sawtooth riblets on NACA4412 airfoil are examined at the low Reynolds number of 1 × 105, and the airfoil is operated at angles of attack (AOAs) ranging from approximately 0° to 12°. The numerical simulation is carried out by employing the SST k–ω turbulence model through the Ansys Fluent, and the effects of the riblets’ length and height on aerodynamic performance and flow characteristics of the airfoil are investigated. The results indicate that the amount of drag reduction varies greatly with riblet length and height and the AOA of airfoil flow. By contrast, the riblets are detrimental to the airfoil in some cases. The most effective riblet length is found to be a length of 0.8 chord, which increases the lift and reduces the drag under whole AOA conditions, and the maximum improvements in both are 17.46% and 15.04%, respectively. The most effective height for the riblet with the length of 0.5 chord is 0.6 mm. This also improves the aerodynamic performance and achieves a change rate of 12.67% and 14.8% in the lift and drag coefficients, respectively. In addition, the riblets facilitate a greater improvement in airfoil at larger AOAs. The flow fields demonstrate that the riblets with a drag reduction effect form “the antifriction-bearing” structure near the airfoil surface and effectively restrain the trailing separation vortex. The ultimate cause of the riblet drag reduction effect is the velocity gradient at the bottom of the boundary layers being increased by the riblets, which results in a decrease in boundary thickness and energy loss.

On the Magnetoelectric Performance of Multiferroic Particulate Composite Materials

In the current work, quantitative analysis of magnetoelectric particulate composite material system explicated the main mechanisms responsible for the below-optimal performance of this class of materials. We considered compliant particulate composite materials, with constituents relevant to technological and scientific interest, leading to 0-3 Terfenol-D/PVDF-TrFE composite samples. To this objective, thick Terfenol-D/PVDF-TrFE films (10-15 µm) were fabricated and analyzed for chemical, mechanical, and magnetic properties to demonstrate their suitability for energy applications in harsh environmental conditions. The vigorous experimental characterization of the composite exemplified the multifunctional properties, quantifying the interrelationship between the composition and performance. We observed that the addition of magnetic particles to the electroactive copolymer matrix resulted in improvement in the mechanical and electrical properties since the particles acted as pinning sites, hindering the deformation of the chains and enhancing polarization. The effective modulus model was amended to account for the crystallization-induced change in material stiffness. We also measured and computed the magnetic particles motion to explicate the detrimental effect of mobility and migration on the overall magnetoelectric coupling performance of the composite. Thereby, we derived an analytical model based on the magnetic force due to the co-presence of alternating and constant magnetic fields, and the viscous drag force due to the viscoelastic properties of the electroactive copolymer matrix. We demonstrated that the mobility of the particles plays a crucial role in the short and long term performance of magnetoelectric coupling in multiferroic particulate composites, uncovering the underpinnings of the dichotomy in performance between experimentally measured and analytically predicted coupling coefficients., thus, allowing for the proposal of new approaches to realize the scientific potential of magnetoelectric particulate composites in energy applications.

Simulations on the rheology of dry magneto-rheological fluid under various working modes

This work studied the rheological properties and magnetorheological (MR) mechanism of dry magnetorheological fluid (MRF) under various working modes. A novel simulation method combining the discrete element method and computational fluid dynamics was developed, in which the bilateral coupling between particles and the flow field of the matrix (air) was considered. The microstructures and mechanical properties in the redispersion process, shear mode, and valve mode were systematically simulated for the first time. The results indicated that dry MRF presented superior redispersion property and response time (several μs) than liquid-based MRFs. In shear mode, the magnetic dipolar force and friction force dominated the evolution of microstructures. In valve mode, the magnetic dipolar force and viscous drag force of air became the main interactions. Magnetic particles aggregated into sturdy chain structures and hindered the airflow. The MR effect in valve mode was the pressure gradient of the matrix, which increased up to 1.08×105 Pa/m with the increasing particle volume fractions and decreased under a large inflow velocity. The best MR effect in valve mode was achieved under a magnetic field of B=63 mT. Simulations revealed the influence of dimensionless Mn and Re number on the MR effect. The pressure gradient of the matrix was controlled by the external field and can be utilized to design a dry MRF valve for precious and transient vibration control. Simulated dimensionless shear stress in shear mode agreed well with experiments. This work will promote the development and applications of novel high-performance MRFs.