Slip in adhesion tests of a Kaolin clay

Adhesion tests were performed on concentrated suspensions of Kaolin clay. At low concentrations samples formed conical deposits on both the top and bottom plates with the central region narrowing to a filament before undergoing breakup. In contrast high concentration samples deformed as a cylinder before apparently fracturing into two pieces. As the concentration of the samples was increased the samples underwent quite different forms of slip which it is shown can be deduced from their respective force distance curves. The type of slip behaviour for a given concentration of clay could be modified with changes to surface roughness, the initial compressive load prior to an experiment and with the separation velocity of the plates. The different slip characteristics appear to arise from the concentration dependent way in which particles interact with the rough surface topography. Graphic Abstract

Prediction of Crosswind Separation Velocity for Fan and Nacelle Systems Using Body Force Models: Part 2: Comparison of Crosswind Separation Velocity with and without Detailed Fan Stage Geometry

Modern aircraft engines must accommodate inflow distortions entering the engines as a consequence of modifying the size, shape, and placement of the engines and/or nacelle to increase propulsive efficiency and reduce aircraft weight and drag. It is important to be able to predict the interactions between the external flow and the fan early in the design process. This is challenging due to computational cost and limited access to detailed fan/engine geometry. In this, the second part of a two part paper, we apply the fan gas path and body force model design process from Part 1 to the problem of predicting flow separation over an engine nacelle lip caused by crosswind. The inputs to the design process are based on NASA Stage 67. A body force model using the detailed Stage 67 geometry is also used to enable assessment of the accuracy of the design process based approach. In uniform flow, the model produced by the design process recreates the spanwise loading distribution of Rotor 67 with a 7% RMS error. Both models are then employed to predict crosswind separation velocity. The two approaches are found to agree in their prediction of the crosswind separation velocity to within 5%.

Blockage correction for pier scour experiments

Commonly used bridge pier scour prediction equations have often employed the quantities of relative coarseness, flow shallowness, and flow intensity to yield a design value for maximum relative scour depth at equilibrium conditions. Predictive methods based on these quantities tend to over-predict scour. Moreover, these equations tend to yield different scour estimates for the same flow conditions. The equations, mostly derived from laboratory estimates of scour, have not considered the influence of the flume sidewall proximity. New experiments are conducted to specifically identify the role of channel blockage on scour. Evaluation of results indicates that the influence of blockage ratio on scour can be described using the value of mean flow velocity along the separating streamline and the ratio of the separation velocity to the critical velocity in the form of new parameter kc. A new scour prediction method is developed and presented.

Efficiency and Critical Velocity Analysis of Gravitational Separator Through CFD Simulation

Oil and gas producing rates have increased rapidly with the development of shale oil and fracturing technology. Besides, advances in horizontal wells have increased the slugging issue, especially in complex geometry wells. Therefore, Artificial lift systems, especially rod-pumps and electrical submersible pumps, always suffer from associated gas and require an economical way to avoid problems like gas lock, gas pound, gas interference and slugging. Among all kinds of the downhole separator, and the gravitational separator are the most economical devices, which can handle severe slugging problems. The rule of thumb liquid maximum downward velocity for the gravitational separator is 0.6 in/s [13, 14]. However, the criterion needs to be improved by considering pressure, temperature and fluid properties. This article first uses CFD simulations to validate the critical liquid velocity and then obtains pressure field, velocity profile, gas distribution and sensitivity factors under complicated field situations. The results could be used to develop an empirical or even a mechanistic efficiency prediction model in the future. In this paper, 2-D simulation is first utilized to study the critical separation velocity and effective parameters. Comparing with Stokes’ law, the simulation shows density, and surface tension have a strong effect of critical separation velocity, while viscosity has lower influence. Then extended 2-D simulations are conducted on different inner tube to annulus connection geometry, which shows a strong effect on separation efficiency. Later on, 3-D CFD simulations are generated based on a newly designed separator by TUALP and an existing design from the Don-Nan separator. Simulations are used to validate 2-D conclusion and illustrate the improvement of the new design.

Effects of Separation Strategy on Deployment of Multitethered Chain-Type Satellite System

This paper investigates the effects of separation strategy and parameters related to deployment on the dynamic behavior of multitethered chain-type satellite system. The system, including several satellites connected by tethers which are considered as massless and straight, is modeled as an extension of a two-body dumbbell tethered system. The dynamic equations of system in absence of perturbations and external disturbances are derived using Newtonian Method. To observe the effect of deployment rate on the motion of system, a parametric analysis of the deployment of a three-body tethered system with different deployment rates is carried out. Moreover, a four-body tethered system is used to investigate the effect of separation strategies on the dynamic behavior of system during the deployment phase. The numerical results suggest that the system with simultaneous separation costs less time to complete the deployment. If the ratio of deployment rates is in consistence with that of their desired lengths, the tethers deployed simultaneously would have a synchronous motion. It is also observed that the system employing separation bolt has a better performance than the system separated by spring mechanism since the larger separation velocity which is not along local vertical may cause a rotation.

Calculation of Kill Probability for Kinetic Energy Rod against TBM Warhead

Kinetic energy rod (KE-rod) warheads are one of the most efficient types against tactical ballistic missile (TBM) that exist today, so the kill probability of KE-rod is extremely important. The paper firstly describes the necessity of KE-rod warhead, and then analyzes the separation velocity of KE-rod, the effective kill radius, static dispersal, dynamic kill zone, and the computational model of mathematical expectation for the hit rod number, and then presents the calculation method of kill probability for KE-rod. Finally, the kill probability of the KE-rod is simulated, the results show that the probability decreases rapidly with the increase of distance between the KE-rod warhead and the target, when the distance between the interceptor and target is less than 5 meters, the kill probability is up to 50%.

Simulation of an Explosive Separation Device Used in Aerospace Craft

In order to study the work principle and separation features of an explosive separation device used in aerospace craft, this research establishes a three-dimensional finite element model based on ABAQUS software. Through simulation of separating process, the work principle is made clear, the separation time and maximum separation velocity are respectively 2.4ms and 8.9m/s. Meanwhile, a measurement system is designed for experiment and verifying the simulation results. The tested separation time and maximum separation velocity are respectively 2.8ms and 7.5m/s ,which shows that the proposed finite element model and simulation can provide references for the research and development of explosive separation devices in aerospace crafts, as well, it is also an effective way to analyze and evaluate the feature of explosive separation device.

Study on the Relationships between Offset Ink Tack Value and its Viscosity, the Separation Velocity

In order to find out the variation law of ink stickiness during the printing, the ink tack value under 9 different linear velocities of ink distributing roller was tested, and the relation equations between tack value and the roller linear velocity were built up. At the same time, the plastic viscosities of 8 offset inks and their tack values under 9 separation velocities were also tested. The study results showed that the higher the linear speed was, the larger the tack value was, and it would stay in a relatively high tack value (regarded as infinite tack value). Also, the printing ink having high viscosity may possess low tack value.

Shock-wave surfing

A phenomenon referred to as ‘shock-wave surfing’, in which a body moves in such a way as to follow the shock wave generated by another upstream body, is investigated numerically and analytically. During the surfing process, the downstream body can accumulate a significantly higher lateral velocity than would otherwise be possible. The surfing effect is first investigated for interactions between a sphere and a planar oblique shock. Numerical simulations are performed and a simple analytical model is developed to determine the forces acting on the sphere. A phase-plane description is employed to elucidate features of the system dynamics. The analytical model is then generalised to the more complex situation of aerodynamic interactions between two spheres, and, through comparisons with further computations, is shown to adequately predict the final separation velocity of the surfing sphere in initially touching configurations. Both numerical simulations and a theoretical analysis indicate a strong influence of the sphere radius ratio on the separation process and predict a critical radius ratio that delineates entrainment of the smaller body within the flow region bounded by the larger body's shock from expulsion. Furthermore, it is shown that an earlier scaling law does not accurately describe the separation behaviour. The surfing effect has important implications for meteoroid fragmentation: in particular, a large fraction of the variation in the separation velocity deduced by previous authors from an analysis of terrestrial crater fields can be explained by a combination of surfing and a modest rotation rate of the parent body.

On the generation of a helicopter aerodynamic database

The GOAHEAD (Generation of an Advanced Helicopter Experimental Aerodynamic Database for CFD code validation) consortium was created in the frame of an EU-project in order to create an experimental database for the validation of 3D-CFD and comprehensive aeromechanics methods for the prediction of unsteady viscous flows. This included the rotor dynamics for complete helicopter configurations, i.e. main rotor – fuselage – tail rotor configurations with emphasis on viscous phenomena like flow separation and transition from laminar to turbulent flow. The wind tunnel experiments have been performed during two weeks in the DNW-LLF on a Mach-scaled model of a modern transport helicopter consisting of the main rotor, the fuselage, control surfaces and the tail rotor. For the sake of controlled boundary conditions for later CFD validation, a closed test section has been used. The measurement comprised global forces of the main rotor and the fuselage, steady and unsteady pressures, transition positions, stream lines, position of flow separation, velocity profiles at the test section inlet, velocity fields in the model wake, vortex trajectories and elastic deformations of the main and tail rotor blades.