The results of experiments on the study of stability of the dome of a water bubble rising through a salt solution are presented. The experimental results are obtained using the PLIF method by recording the flow in the plane that coincides with the axis of symmetry of the bubble, The experiments demonstrate the possibility of the development of instability in the vicinity of the pole of the dome of such a bubble in accordance with the previously published results of computational simulation.

The problem of acceleration in a cylindrical channel by a compressed gas (in particular, by the detonation products of a mixture of acetylene and oxygen) of a thin flat striker is related to the problem of a falling sheet of paper", since the movement of the striker in the channel is unstable with respect to the lateral displacement. This can lead to a violation of the symmetry of the flight of the striker, its skew and a sharp decrease in the achieved speed of the striker. The possibility of preserving the orientation of the striker by limiting its lateral displacement by a uniform arrangement on the inner surface of the channel (on the forming surface) of several thin strands of polymer fishing line is experimentally shown.

The technique of experimental investigation of the effect of an accelerated shear flow on the development of the Rayleigh—Taylor (RT) instability at the interface of two fluids at a small Atwood number is developed. Using a counterpart of the laser sheet method (laser induced fluorescence) the data on the structure of the RT mixing zone are obtained and the instability stabilization under the action of an accelerated shear flow is confirmed.

The task of accelerating a thin plane impactor in a cylindrical channel with high-pressure gas (in particular, detonation products of acetylene–oxygen fuel mixture) encounters the well-known problem of “falling paper sheet” since the impactor motion in the channel is also unstable with respect to lateral (radial) displacements. This displacement can lead to breakage of the symmetry of flight, skewness of the impactor, and a sharp decrease in the achieved velocity. It has been experimentally established that the impactor orientation can be retained by limitation of its lateral shifts with the aid of several thin filaments of a polymer thread (fishing line) arranged uniformly on the inner channel surface along the cylinder generatrix.

The interface between two media of different densities (contact boundary) moving with an acceleration directed from the less dense medium to the more dense one is unstable (Rayleigh–Taylor instability) [1, 2]. The initial perturbations of the interface grow indefinitely and, as a result, a medium mixing zone growing with time is formed at the interface. The structure of such a mixing zone at gas–gas and gas–liquid interfaces is discussed on the basis of laboratory experiments on shock tubes of various types. It is concluded that the regions of turbulent and laminar flows are combined in the mixing zone.

The results of experiments researching the stability of the dome of a large water bubble rising in a salt solution are presented. The experiments demonstrate the suppression of the Rayleigh–Taylor instability on the dome of the rising bubble with the Atwood number being A ≪ 1. The intensive development of the Kelvin–Helmholtz instability on the lateral surface of the bubble is observed as it rises. The stability of the dome of the rising bubble is explained by the action of an accelerated shear flow of water over the bubble surface. The results of computational modeling of the problem by the STAR-CCM + program are presented.

As fluid flows through a conventional wind or hydro turbine, it slows from losing energy to extraction from a turbine and spreads out to a wider area. This results in a loss of turbine efficiency. In order to exploit wind or water flow power more effectively, it was suggested to place the turbine inside a system of specially designed airfoils ('a flow booster'). One part of the booster ('a nozzle') improves the turbine performance by speeding up the flow acting on the turbine blades. The other part of the accelerating system ('a diffuser') creates a field of low pressure behind the turbine which helps to draw more mass flow to the turbine and avoid the loss of efficiency due to flow deceleration. The flow booster accumulates the kinetic energy of the flow (e.g. river flow or wind) in a small volume where the smaller turbine can be installed. Another possible application of the booster could be the improvement of wind turbine efficiency during low wind period. The present paper also discusses the possibility of kinetic energy accumulation by the use of several accelerating systems of different sizes-the smaller one can be installed inside the bigger one. It helps to accumulate even more kinetic energy on the turbine blades. We call this method the kinetic energy cumulation. Lab and field experiments and CFD simulations of shrouded turbine demonstrate significant increase in velocity in comparison of those for conventional (bare) turbines.

When approaching a conventional wind turbine, the air flow is slowed down and widened. This results in a loss of turbine efficiency. In order to exploit wind or water flow power as effectively as possible, it was suggested that the turbine should be placed inside a shroud, which consists of 4 wing-shaped surfaces. Two internal air foils improve the turbine performance by speeding up the flow acting on the turbine blades, two external wings create a field of low pressure behind the turbine, thus, helping to draw more mass flow to the turbine and avoid the loss of efficiency due to flow deceleration. The system accumulates kinetic energy of the flow in a small volume where the smaller ( and therefore, cheaper) turbine can be installed. A smaller system can be installed inside the bigger one, which would help to accumulate even more kinetic energy on the turbine. This method implies kinetic energy summation with local flow redistribution. Both experiments and CFD simulations demonstrate a significant increase in velocity and generated mechanical power in comparison to those for a bare turbine.

We describe a method for accelerating a thin (~1 mm thick) striker with a diameter of 35 mm in a shock tube channel up to velocities above to ~275 m/s under the pressure of detonation products of acetylene–oxygen fuel mixture. Impact of this striker on a ~1-cm-thick water layer generates a nonstationary decaying shock wave (Taylor wave) with amplitude of ~0.2 GPa on escape from the free surface.

Methods of laboratory modeling of 2D water flows in a rectangular channel are developed. The flow is produced in a vertical tube of a rectangular cross section when water flows through the hole in the bottom of the tube. In the setup, a short-term (up to ∼15 s) laminar water flow with a velocity up to about 18 cm/s is produced. The methods for recording the flow velocity and the type of the flow past models of various shapes are developed

A method for videotaping micro-objects by means of overhead projection is described. This method allows recording microparticles, including rapidly moving ones, whose size is no less than 1 µm.

The instability of the free boundary of a thin (1 mm) water layer under the action of a Taylor wave (80 MPa), which is created by a laser pulse, has been experimentally studied. The experimental results demonstrate the capabilities of the laser Doppler method for the continuous recording of a flying object (PDV method) [O. T. Strand, D. R. Goosman, and C. Martinez, Rev. Sci. Instrum. 77, 0831081 (2006)] for studying this problem.

We discuss the results of experiments that illustrate some features of a turbulent mixing zone (TMZ) structure at a gas–liquid interface (Rayleigh–Taylor instability) and at a gas–gas interface accelerated by shock waves (Richtmyer–Meshkov instability). The important feature is the existence of a heavier substance concentration (density) jump at the interface between the heavy medium and the TMZ. It is found that the existence of this jump is a generic feature of any developed TMZ and is the necessary condition for its continuous development. In the case of a gas–liquid interface, the stable existence of this jump is connected with the stability of the cupola of gas bubbles penetrating into the liquid in a TMZ. The important feature of the development of interface instability accelerated by an unsteady shock is the decaying ability (up to full suppression) of the interface instability in the case when a decaying wave passes through the interface in the direction from light gas to heavy gas.

During the study of a bath-tub vortex formed in water flowing out through the hole in a vessel's bottom, a methodology was developed that enables controlling the change of in-vessel water level by continuous replenishment. The controlled rate of replenishment enables not only compensating for the loss of drained water and maintaining it at a constant level, but also increasing such a level. Enhancement of water level at different times after the formation of the bath-tub vortex leads to the gradual extinction of the vortex until its complete disappearance when a certain critical level of water in the vessel is achieved. A bath-tub vortex shape with a decrease of in-vessel water level and increase differs significantly.

An unusual phenomenon called “whirlpool splitting” by analogy with an axe splitting wood logs was experimentally observed. In this experiment, a metal ruler, set vertically on the bottom of the aquarium on the hole axis during flowing out of water has led to the separation of a whirlpool into two formed on both sides of the rule and existed until the end of draining. The paper describes some results of experiments based on the research of this phenomenon

The results of investigating the possibility of extinguishing of the flames by the steam explosion of hermetically sealed thin-walled capsules filled by water (RF patent No 2295370, 2396602, 2406552, 2401674) are presented. The experiments were performed with a few millimeters size glass capsules: a)spherical (diameter d = 7 mm, wall thickness Δ = 0,23-0,25mm, the volume of water in the capsule of 0.14 ml) and b)cylindrical shape (diameter d = 5 mm , the length of the capsule 45 mm, wall thickness Δ = 0,40,5 mm and the volume of water in the capsule 0.3 ml). The capsules were heated by flame of different types gas burners.

Free fall of an approximately spherical water ball with a volume within 0.1–0.5 l from the state of rest at an altitude of up to ∼5 m was experimentally studied. The deformation of the liquid ball under the action of aerodynamic forces and instabilities leads to its disintegration with the formation of a droplet cloud with rapidly growing dimensions in both longitudinal (vertical) and lateral directions.

This paper addresses features of hydrodynamic instability growth on shock arrival at a free surface of condensed matter with deterministic initial perturbations. Richtmyer-Meshkov instability growth processes with initial two-dimensional (2D) and 3D perturbations are considered. Experimental diagnostics included pulsed radiography and a two-piston shock-tube technique. It is shown experimentally that the growth of perturbations strongly depends on material compression in the shock tube. In the hydrodynamic approximation, when the shock Mach number is M > 1, the growth rate of initial 2D and 3D perturbations is the same. Under weak shock compression conditions (M similar to 1), it may happen that initial 3D perturbations will not grow at all. Our results conflict with theoretical concepts of perturbation growth associated with Richtmyer-Meshkov instability, according to which the growth rate of initial 3D perturbations at the nonlinear stage should always be higher than the growth rate of 2D perturbations for the same a/lambda ratios. A computational physics model of the process of interest was developed based on LEGAK simulations.