A discussion on deformation of solids by the impact of liquids, and its relation to rain damage in aircraft and missiles, to blade erosion in steam turbines, and to cavitation erosion - Rain erosion properties of materials

1966 ◽  
Vol 260 (1110) ◽  
pp. 168-181 ◽  
Keyword(s):  
High Speed ◽  
Cavitation Erosion ◽  
High Speed Photography ◽  
Steam Turbines ◽  
Quantitative Measurements ◽  
Wide Range ◽  
Erosion Properties ◽  
Properties Of Materials ◽  
The Impact ◽  
Rain Erosion

A rotating arm apparatus capable of circumferential speeds up to 475 m/s (Mach 1.4) has been used to make quantitative measurements of the velocity and angle dependence of ram erosion for a wide range of materials. It has been possible to relate the mechanical properties of some materials with their rain erosion resistance. The behaviour of the drops during impact has been studied by high speed photography.

A discussion on deformation of solids by the impact of liquids, and its relation to rain damage in aircraft and missiles, to blade erosion in steam turbines, and to cavitation erosion - Damage to solids caused by cavitation

1966 ◽  
Vol 260 (1110) ◽  
pp. 245-255 ◽  
Keyword(s):  
Mechanical Properties ◽  
Cavitation Erosion ◽  
Cavitation Resistance ◽  
Steam Turbines ◽  
Single Event ◽  
Cavitation Damage ◽  
Erosion Damage ◽  
Highly Sensitive ◽  
Wide Range ◽  
The Impact

This paper describes the early stages of cavitation damage observed in cavitating venturi tunnels. The cavitating fluids were water and mercury, and a wide range of specimen materials were used. The damage was found to consist of single-event symmetical craters and irregular fatigue-type failures. The degree of damage was highly sensitive to minor flow perturbations, and this is discussed. The effect of stress level in the specimen before testing, and relations between cavitation resistance and the mechanical properties of the materials are considered.

A discussion on deformation of solids by the impact of liquids, and its relation to rain damage in aircraft and missiles, to blade erosion in steam turbines, and to cavitation erosion - High speed liquid impact

1966 ◽  
Vol 260 (1110) ◽  
pp. 79-85 ◽  
Keyword(s):  
High Speed ◽  
Cavitation Erosion ◽  
High Strain ◽  
Strain Rates ◽  
Steam Turbines ◽  
High Speeds ◽  
Liquid Impact ◽  
Deformation Patterns ◽  
The Impact ◽  
Very High

A study has been made of the deformation at high strain rates of solids under the impact of liquids. A method is described for projecting a short liquid jet against a solid surface at speeds up to 1200 m/s. The flow of the liquid and the deformation of the solid during impact have been examined by high speed photographic methods. An attempt has been made to measure the magnitude and duration of the load by means of a piezoelectric pressure transducer. There is evidence that the liquid behaves initially on impact in a compressible manner. Part of the deformation of the solid is due to this compressible behaviour and part to the erosive shearing action of the liquid flowing at very high speeds out across the surface. The mode of deformation in brittle and in plastically deforming materials has been investigated. The deformation patterns produced are shown to be characteristic of liquid impact. The predominating mechanism of deformation depends on the mechanical properties of the solid and on the velocity of impact.

A discussion on deformation of solids by the impact of liquids, and its relation to rain damage in aircraft and missiles, to blade erosion in steam turbines, and to cavitation erosion - Practical aspects of rain erosion of aircraft and missiles

1966 ◽  
Vol 260 (1110) ◽  
pp. 161-167 ◽  
Keyword(s):  
High Speed ◽  
Protective Coatings ◽  
Material Surface ◽  
Steam Turbines ◽  
Functional Requirements ◽  
Design Problems ◽  
Factors Affecting ◽  
Practical Applications ◽  
The Impact ◽  
Rain Erosion

All-weather operational requirements have added considerably to aircraft and missile design problems as the effects of various meteorological hazards, predominantly rain, are aggravated by high speed flight. Typical damage patterns are reproduced and discussed. The problem of rain erosion is reviewed with regard to the functional requirements of the components, the flight plan of the vehicle and the occurrence of rain over the geographical terrain of operation. The factors affecting rain erosion characteristics such as type of material, surface finish, shape of component, speed and rainfall intensity are discussed and empirical data derived. The translation of significant results into practical applications is described with particular reference to supersonic transport aircraft. Details given of equipment for the simulation of rain erosion are concerned principally with the R. A. E. ‘whirling arm’ and rocket runway high speed sled techniques. Correlation of test results from these facilities with those from flight tests are briefly discussed. Degree of erosion of a material is defined in relation to the particular application of the material and details are given of the characteristics of numerous materials, both metals and non-metals. The utilization of these materials for such applications as radomes, transparencies, high temperature materials, de-icing systems are briefly discussed together with methods of extending the rain erosion ‘life’ of materials by design or by use of protective coatings.

Drop Impact Dynamics: Impact Force and Stress Distributions

2021 ◽  
Vol 54 (1) ◽  
Author(s):  
Xiang Cheng ◽  
Ting-Pi Sun ◽  
Leonardo Gordillo
Keyword(s):  
High Speed ◽  
Impact Force ◽  
Drop Impact ◽  
Impact Dynamics ◽  
Annual Review ◽  
Publication Date ◽  
High Speed Photography ◽  
Stress Distributions ◽  
Wide Range ◽  
The Impact

Dynamic variables of drop impact such as force, drag, pressure, and stress distributions are key to understanding a wide range of natural and industrial processes. While the study of drop impact kinematics has been in constant progress for decades thanks to high-speed photography and computational fluid dynamics, research on drop impact dynamics has only peaked in the last 10 years. Here, we review how recent coordinated efforts of experiments, simulations, and theories have led to new insights on drop impact dynamics. Particularly, we consider the temporal evolution of the impact force in the early- and late-impact regimes, as well as spatiotemporal features of the pressure and shear-stress distributions on solid surfaces. We also discuss other factors, including the presence of water layers, air cushioning, and nonspherical drop geometry, and briefly review granular impact cratering by liquid drops as an example demonstrating the distinct consequences of the stress distributions of drop impact. Expected final online publication date for the Annual Review of Fluid Mechanics, Volume 54 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Cavitation erosion by single laser-produced bubbles

1998 ◽  
Vol 361 ◽  
pp. 75-116 ◽  
Author(s):  
A. PHILIPP ◽  
W. LAUTERBORN
Keyword(s):  
Impact Velocity ◽  
High Speed ◽  
Cavitation Erosion ◽  
Bubble Radius ◽  
Solid Boundary ◽  
Material Surface ◽  
High Speed Photography ◽  
Single Laser ◽  
The Moment ◽  
The Impact

In order to elucidate the mechanism of cavitation erosion, the dynamics of a single laser-generated cavitation bubble in water and the resulting surface damage on a flat metal specimen are investigated in detail. The characteristic effects of bubble dynamics, in particular the formation of a high-speed liquid jet and the emission of shock waves at the moment of collapse are recorded with high-speed photography with framing rates of up to one million frames/s. Damage is observed when the bubble is generated at a distance less than twice its maximum radius from a solid boundary (γ=2, where γ=s/Rmax, s is the distance between the boundary and the bubble centre at the moment of formation and Rmax is the maximum bubble radius). The impact of the jet contributes to the damage only at small initial distances (γ[les ]0.7). In this region, the impact velocity rises to 83 m s−1, corresponding to a water hammer pressure of about 0.1 GPa, whereas at γ>1, the impact velocity is smaller than 25 m s−1. The largest erosive force is caused by the collapse of a bubble in direct contact with the boundary, where pressures of up to several GPa act on the material surface. Therefore, it is essential for the damaging effect that bubbles are accelerated towards the boundary during the collapse phases due to Bjerknes forces. The bubble touches the boundary at the moment of second collapse when γ<2 and at the moment of first collapse when γ<1. Indentations on an aluminium specimen are found at the contact locations of the collapsing bubble. In the range γ=1.7 to 2, where the bubble collapses mainly down to a single point, one pit below the bubble centre is observed. At γ[les ]1.7, the bubble shape has become toroidal, induced by the jet flow through the bubble centre. Corresponding to the decay of this bubble torus into multiple tiny bubbles each collapsing separately along the circumference of the torus, the observed damage is circular as well. Bubbles in the ranges γ[les ]0.3 and γ=1.2 to 1.4 caused the greatest damage. The overall diameter of the damaged area is found to scale with the maximum bubble radius. Owing to the possibility of generating thousands of nearly identical bubbles, the cavitation resistance of even hard steel specimens can be tested.

Hydraulic Performance and Jet Breakup Characteristics of the Impact Sprinkler with Circular and Non-circular Nozzles

2019 ◽  
Vol 35 (6) ◽  
pp. 911-924 ◽  
Author(s):  
Yue Jiang ◽  
Hong Li ◽  
Chao Chen ◽  
Lin Hua ◽  
Daming Zhang
Keyword(s):  
High Speed ◽  
Cone Angle ◽  
Hydraulic Performance ◽  
High Speed Photography ◽  
Breakup Process ◽  
Breakup Length ◽  
Jet Breakup ◽  
Circular Jets ◽  
Square Jets ◽  
The Impact

HighlightsThe hydraulic performance of the impact sprinkler with circular and non-circular nozzles were measured.A High-Speed Photography (HSP) technique was employed to extract the jet breakup process of the impact sprinkler.Two index equations of jet characteristic lengths and equivalent diameters of non-circular nozzles were fitted. Abstract. An experiment was carried out to investigate the hydraulic performance of an impact sprinkler by using circular and non-circular nozzles. A High-Speed Photography (HSP) technique was employed to extract the breakup process and flow behavior of low-intermediate pressure water jets issued from the different types of orifices. These orifices were selected by the principle of equal flowrate with the same pressure. Moreover, two characteristic lengths: the jet breakup length and the initial amplitude of surface wave were measured. It was found that the sprinkler with circular nozzles produced the largest radius of throw followed by square nozzles and regular triangular nozzles when the cone angle of nozzle and pressure were unchanged, while the sprinkler with regular triangular nozzle had the best variation trend of water distribution and combination uniformity coefficient. Regular triangular jets exhibited a higher degree in breakup and the shortest breakup length compared with the square jets and the circular jets. The initial amplitudes of surface waves of regular triangular jets were larger than the square jets and the circular jets with the same cone angle. Two index equations of jet characteristic lengths and equivalent diameters of both circular and non-circular orifices were fitted with a relative error of less than 10%, which means the fitting formulas were accurate. Keywords: Breakup length, Fitting formula, Hydraulic performance, Initial amplitude, Non-circular jets.

A discussion on deformation of solids by the impact of liquids, and its relation to rain damage in aircraft and missiles, to blade erosion in steam turbines, and to cavitation erosion - The formation of microjets in liquids under the influence of impact or shock

1966 ◽  
Vol 260 (1110) ◽  
pp. 94-95 ◽  
Keyword(s):  
Cavitation Erosion ◽  
Concave Surface ◽  
Short Film ◽  
Steam Turbines ◽  
Small Cavity ◽  
The Impact

If a small cavity or bubble in a liquid is subject to impact or to shock, tiny Munroe jets may be formed on its concave surface. The velocity of these microjets may be high. A short film illustrating the formation of these small jets in cavities and in coalescing drops was shown.

A discussion on deformation of solids by the impact of liquids, and its relation to rain damage in aircraft and missiles, to blade erosion in steam turbines, and to cavitation erosion - The collapse of cavitation bubbles and the pressures thereby produced against solid boundaries

1966 ◽  
Vol 260 (1110) ◽  
pp. 221-240 ◽  
Keyword(s):  
Cavitation Erosion ◽  
Experimental Information ◽  
Liquid Jets ◽  
Steam Turbines ◽  
Jet Formation ◽  
Cavitation Damage ◽  
Cavity Collapse ◽  
New Ideas ◽  
The Impact ◽  
Shape Changes

Our object is to present a broad review of this subject as a branch of hydrodynamics, referring both to the well known ‘implosion’ mechanism first analysed by Lord Rayleigh and, more particularly, to the recently perceived possibility that effects of equally great violence, such as to damage solid boundaries, may arise through the impact of liquid jets formed by collapsing cavities. In §2 a few practical facts about cavitation damage are recalled by way of background, and then in §3 the significance of available theoretical and experimental information about cavity collapse is discussed. The main exposition of new ideas is in §4, which is a review of the factors contributing to shape changes and eventual jet formation by collapsing cavities. Finally, in §5, some new experimental observations on the unsymmetrical collapse of vapour-filled cavities are presented.

Flow Characteristics of Rectangular Liquid Jets Injected Into Low Subsonic Crossflow

2019 ◽  
Author(s):  
M. Tadjfar ◽  
A. Jaberi ◽  
R. Shokri
Keyword(s):  
High Speed ◽  
Flow Characteristics ◽  
Combustion Efficiency ◽  
Liquid Jets ◽  
High Speed Photography ◽  
Aspect Ratios ◽  
Jet Trajectory ◽  
Wide Range ◽  
Circular Holes ◽  
Subsonic Crossflow

Abstract Perpendicular injection of liquid jets into gaseous crossflow is well-known as an effective way to obtain good mixing between liquid fuel and air crossflow. Mostly, injectors with circular holes were used as the standard method of fuel spraying. However, recently a great attention to injectors with non-circular holes has emerged that aims to improve the quality of fuel mixing and consequently combustion efficiency. In the present work, rectangular injectors with different aspect ratios varying from 1 to 4 were experimentally studied. Using a wind tunnel with maximum air velocity of 42 m/s, tests were performed for a wide range of flow conditions including liquid-to-air momentum ratios of 10, 20, 30 and 40. Backlight shadowgraphy and high speed photography were employed to capture the instantaneous physics of the liquid jets discharged into gaseous crossflow. The flow physics of the rectangular liquid jets were investigated by means of flow visualizations. Different regimes of flow breakup including capillary, arcade, bag and multimode were observed for rectangular jets. Moreover, a new technique was used to calculate the trajectory of the liquid jets. It was shown the nozzle’s shape has no significant effect on jet trajectory. Also, the momentum ratio was found to has a profound effect on jet trajectory.

Free Space Optical Communication System under Different Weather Conditions

2019 ◽  
Vol 0 (0) ◽  
Author(s):  
Mohammad Yawar Wani ◽  
Hitesh Pathak ◽  
Karamjit Kaur ◽  
Anil Kumar
Keyword(s):  
Attenuation Coefficient ◽  
Optical Communication ◽  
Free Space ◽  
Communication Systems ◽  
High Speed ◽  
Free Space Optical Communication ◽  
Free Space Optical ◽  
Wide Range ◽  
Space Optical Communication ◽  
The Impact

AbstractFree space optical communication systems (FSO’s) have surfaced as admired means of communication in the past few years. High speed of operation, low bandwidth requirements and system reliability are the major factors responsible for their wide range of applications. These communication systems use air as a medium of transmission. Since there is no component like fiber or cable, but air is only medium, the variations in atmospheric conditions play a vital role in performance of these networks. The reason behind is that the conditions like presence of humidity, haze, snowfall, rain, dust or smoke changes the attenuation coefficient of medium. The raised attenuation levels results in increased losses and need to be carefully monitored. The present work analyzes the influence of rain on the performance of FSO network in terms of quality of transmission. The paper discusses the impact of rainfall on attenuation coefficient of air. Then impact of this attenuation on network transmission is presented in terms of BER and Q-factor. In order to demonstrate the impact, BER and Q-value is calculated for 10 Gbps FSO link for clear weather and rainfall conditions.

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