Hydroelectric power plants for small rivers

Comparative analysis of methods of obtaining electricity from a renewable energy source is carried out. Various designs and op-tions for small hydroelectric power plants have been proposed. Positive and negative factors of structures under consideration and their impact on the environment are analyzed. The main characteristics of the flow (speed, head) for the choice of the optimal variant of hydroelectric power plant have been determined. Three variants of impellers for free-flow hydroelectric power plants are proposed with a comparison of the efficien-cy of each variant. An analysis was carried out and an impeller based on a Darrieus rotor was selected for further research. Simulation was performed in the Flow Simulation program. The initial data for the design of Darrieus rotor operating in a liquid were the diameter and width of the impeller. The calculations involved a rotor with straight and swirling blades. The swirling blades rotor is self-starting. In the course of the calcula-tion, the speed of the liquid flow approaching the rotor and the rotor speed were changed. As a result of cal-culation, the value of the positive moment for self-starting was determined, which occurs at an incident flow velocity of at least 1.3 m/s.

The deceleration of small charged bodies in a rarefied plasma

The purpose of this work is to create a method for determining the aerodynamic characteristics of fine particles in a highly rarefied plasma. The created method is based on the theorem on the change in momentum imparted to the body. The “body+surrounding plasma” system was considered to be closed; therefore, the change in the momentum of the body is equal in the impulse of the incident flow and is opposite to it in direction. The change in the pulse flux is calculated using the statistical method. To compare the results and approbation of the calculation method, the deceleration forces of a spherical body in a flow of neutral gas were determined. Next, we calculated the drag coefficient from the side of the charged plasma component. The calculation results are presented in the graphs.

Application of the time-frequency technique for analysis of velocity fluctuations in the wake of a teardrop profile in the presence of a localized flow inhomogeneity

Experimental simulation of the inhomogeneity of the incident flow localized in time and space on a bluff tear-drop airfoil is carried out. It is shown that in the region outside the aerodynamic wake of the tear-drop airfoil, the presence of inhomogeneity leads to an increase in the amplitudes of velocity fluctuations in a wide frequency range. In the region inside the wake, the presence of inhomogeneity leads to the suppression of velocity fluctuations at the frequency of vortex shedding by a factor of 2–3 in amplitude. The intensification of fluctuations at frequencies above the main one was also noted, and there was no effect on fluctuations at lower frequencies.

Hydrodynamic study of the flow developed around a bare hull ship in static drift motion

The present study gives a Computational Fluid Dynamics (CFD) based insight into the three-dimensional incident flow developed around a very large crude carrier ship during static drift motion. The research proposes a set of virtual Planar Motion Mechanism (PMM) tests of “static drift” type conducted for a number of seven drift angles in the range of -9o to +9o . The emergence and development of vortical structures along the 1:58 KRISO Very Large Crude Carrier 2 (KVLCC2) tanker model are examined and explained, the influence of the considered drift angles being highlighted.

Suppression of galloping oscillations by injecting a high-frequency excitation

Galloping is an aeroelastic instability which incites oscillatory motion of elastic structures when subjected to an incident flow. Because galloping is often detrimental to the integrity of the structure, many research studies have focused on investigating methodologies to suppress these oscillations. These include using passive energy sinks, altering the surface characteristics of the structure, actively changing the shape of the boundary layer through momentum injection and using feedback control algorithms. In this paper, we demonstrate that the critical flow speed at which galloping is activated can be substantially increased by subjecting the galloping structure to a high-frequency non-resonant base excitation. The average effect of the high-frequency excitation is to produce additional linear damping in the slow response which serves to suppress the galloping instability. We study this approach theoretically and demonstrate its effectiveness using experimental tests performed on a galloping cantilevered structure. It is demonstrated that the galloping speed can be tripled in some experimental cases. This article is part of the theme issue ‘Vibrational and stochastic resonance in driven nonlinear systems (part 2)’.

Влияние локального нагрева набегающего потока на уровень звукового удара от тонкого тела, находящегося в аэродинамической тени за диском

Calculations are performed for a sonic boom generated by two bodies (a disk and a thin body of revolution) in the case of local heating of the incident air flow. The bodies are in a heat trail behind the heating region. The thin body is in an aerodynamic shadow behind the disk. The Mach number of the cold air flow is 2. The calculations are carried out using the combined method of "phantom bodies". It is concluded on the basis of the calculations that the level of a sonic boom can be effectively suppressed by simultaneously using the heating of the incident flow and the aerodynamic shadow behind the disk.

Метод управления аэродинамическим сопротивлением цилиндра с газопроницаемыми пористыми вставками путем регулирования донного давления

The results of an experimental and numerical study of a supersonic (M = 7) flow around a hollow cylinder with gas-permeable porous inserts located along the flow are presented. The possibility of controlling the aerodynamic drag of the model by passing a part of the incident flow into the bottom area through gas-permeable porous inserts is shown. The flow rate of air directed to the bottom region to control the resistance was controlled by heating the porous inserts with an electric glow discharge.

Numerical modelling of the oscillatory flow effect around submarine pipeliness

This work describes the dynamics of an underwater pipeline subjected to an incident flow composed of a uniform flow and a sinusoidal component. The motion equations of the pipeline and the fluid flow around the pipeline are solved simultaneously with a numerical model that considers in-line oscillations (one degree of freedom) and a second numerical model that additionally includes cross flow (two degrees of freedom). The amplitude response and drag forces on the pipe are compared for both models considering parameters such as the difference between the excitation and natural frequencies of pipelines and the relative value between the sinusoidal and uniform components of the incident flow. Important differences in numerical predictions of both models are observed when the excitation frequency is greater than the natural frequency of the system and when the amplitude of the oscillatory component of the incident flow is greater than the amplitude of the uniform flow.

Influence of the Composition of the Hybrid Filler on the Atomic Oxygen Erosion Resistance of Polyimide Nanocomposites

The structure and properties of nanocomposites based on organosoluble polyimide (PI) and branched functional metallosiloxane oligomers with different types of central metal atoms (Al, Cr, Fe, Zr, Hf and Nb) were investigated. Under the same weight content of the filler, the geometric parameters of the nanoparticles and thermal properties of the nanocomposites did not exhibit a direct relationship with the ability of the materials to withstand the incident flow of oxygen plasma. The atomic oxygenerosion resistance of the filled PI films was influenced by the composition of the hybrid fillerand the type of metal atom in the hybrid filler in the base metallosiloxane oligomer. To determine the effectiveness of the nanoparticles as protective elements of the polymer surface, the nanocomposite erosion yields pertaining to the concentration of the crosslinked organo–inorganic polymer forming the dispersed phase were determined and expressed in mmol per gram PI. The filler concentration in the polymer, expressed in these units, allows for comparison of the efficiency of different nanosize fillers for use in fabricating space survivable coatings. This can be important in the pursuit of new precursors, fillers for fabricating space survivable polymer composites.