Analytical simulation of influential parameters affecting grooved wet clutches performance underdisengagement condition

Innovating new approaches and effective methods to improve the efficiency of mechanical systems in terms of energy losses and environmental effects serve as an attractive domain for researchers and industries. Wet clutches are widely used in power transmission systems in automotive and other tribological mechanisms. The wet clutch has two functional modes; under the engaged state, in which two disks come into contact to each other, and under disengagement the plates are located at a very short distance from each other, and oil flows between them. In disengaged state, the differential speed of driving and driven units causes oil shearing within the clearance which leads to transmission of certain amount of drag torque from the driving to the output shaft. This transferred drag torque is distinguished as power loss in form of heat. The governing physical relation based on continuity equation and Navier–Stokes equations reveals that in a certain rotational velocity, the pressure gradient at the outer radius of the clutch becomes null, and, in this circumstance, aeration occurs that is known as critical rotation speed. Experimental findings provide evidence that geometry manipulation and considering grooves over the frictional disk, reduces the critical rotational speed. But there is a shortage of physical analytical relations to predict the pressure gradient in grooved wet clutches. Therefore, this article is aimed to introduce analytical model to evaluate grooved wet clutches performance in terms of drag torque and critical rotational speed under single-phase flow condition.

Effect of Rotation on Leakage and Windage Heating in Labyrinth Seals With Honeycomb Lands

One of the basic assumptions of the traditional labyrinth seal leakage calculation is that rotation has minimal or no effect on seal leakage. With the advancement of gas turbine technology, to achieve high performance, seals are run at tight clearances and very high rotational speeds. Due to tight clearances and high speeds, the temperature rise across the seal can be very significant in reducing the seal flow due to the Raleigh line effect. The influence of rotation on the flow dynamics inside the seal region has not previously been studied in detail. In this study the effect of rotation is studied for smooth and honeycomb cells at various seal clearances and rotational speeds. The main objective of this study is to understand the influence of rotation on seal leakage. However, the effect of rotation on swirl and windage heating is also investigated. For this study, the author leveraged the validated 3D computational fluid dynamics methodology for a stationary and rotating labyrinth from previous studies. However, before performing studies on rotation, the numerical modeling approach is benchmarked against experimental data on rotation with smooth stator lands by Waschka et al. The numerical predictions show good agreement with the experimental data. As the rotational speed increases, seal discharge coefficient remains constant until a critical rotational speed is reached. This critical speed is shown to depend non-dimensionally on the ratio of Taylor number to Reynolds number (Ta/Re). As Ta/Re increases above 0.1, seal discharge coefficient can reduce by up to 25% depending on the seal clearance, fin tip speed, and honeycomb cell size.

Nonlinear Reduced Dynamic Model of Turbofan Engine for Investigation of Engine Structural Frame Vibrations After Fan Blade Out Event

This paper proposes an approach to construct a nonlinear dynamic model of a whole turbofan engine using the static condensation technique. Nonlinear dynamic behavior of the engine is described by a matrix differential equation, where the right side of the equation represents unbalance load and contact loads between the blades and casings, low-pressure (LP) shaft and high-pressure shaft. Elements of the matrices are calculated by static condensation of three-dimensional finite element models of rotors, casings, engine mounts, and wing attachment system. On the basis of the proposed approach, a model of the entire engine was constructed. The model considered contact interactions as well as effects associated with both instantaneous application of the unbalance load and the passage of the LP rotor through the critical rotational speed during the deceleration phase. The model has a modular structure that allows for the easy replacement of individual components and analysis of the various engine structural frame options. The results of engine structural frame load calculations after a fan blade-out event and during deceleration of the rotors to windmill mode are presented in this paper. In addition, the influence of the flexibility of fan supports, blade wheel nonlinear radial stiffness, and slowdown rates of rotors on load magnitudes are analyzed.

Vibration characteristics of filament wound composite tubes applied to the intermediate shaft in ship propulsion system

In this study, the CFRP shafts made up of T700-SC multilayered composites have been designed to replace the steel shaft of a ship. An important design variable to be considered when designing composite material intermediate shafts is the natural frequency for resonance avoidance at critical rotational speed and torsional strength for axial load. In order to satisfy these, strength and modal analysis were performed. In order to minimize the deformation of the shape due to the residual stress after mandrel removal, it was laminated by axial symmetry. The fibers orientation angle has a great influence on the natural frequency of the drive shaft. The carbon fiber should be closely oriented at [Formula: see text] to improve the modulus of elasticity in the direction of length of the intermediate shaft and to increase the natural frequency. Also, the optimum fiber orientation for maximum torsional strength should be close to [Formula: see text]. The stacking pattern and the stacking order were finally decided considering the results of the finite element analysis (FEA).

Tribological performances of graphite–MoS2 coating at various high temperatures

The tribological performances of the graphite–MoS2 coating deposited on the disc specimen, whose material is GCr15 steel, are experimentally investigated under high temperatures. Effects of graphite content, applied load, rotational speed and test temperature on the coefficient of friction and wear scar width of the coating are evaluated. The graphite–MoS2 coating with 20 wt% graphite addition exhibits the relatively small coefficient of friction and wear scar width at 200 ℃. At or beyond 400 ℃, the coating's lubricating effect is severely deteriorated with the testing time. At 200 ℃, there exists a critical applied load of 10 N and a critical rotational speed of 1250 rpm beyond which the MoS2 coating with 20 wt% graphite content is worn through and brings out a large coefficient of friction. The test results indicate that adding 20 wt% to 33 wt% graphite to MoS2 coating leads to an obvious reduction of the coefficient of friction and wear scar width for the coating at 200 ℃.

MACHINE VISION DETECTION OF THE CIRCULAR SAW VIBRATIONS

Dynamical properties of rotating circular saw blades are crucial for both production quality and personnel safety. This paper presents a novel method for monitoring circular saw vibrations and deviations. A machine vision system uses a camera and a laser line projected on the saw’s surface to estimate vibration range. Changes of the dynamic behaviour of the saw were measured as a function of the rotational speed. The critical rotational speed of the circular saw blade as well as the optimal rotational speed of the saw were detected.

Formulas for Calibration of Rheological Parameters of Bingham Fluid in Couette Rheometer

We propose simple formulas for calibration of rheological parameters of Bingham fluid using a co-axial cylinder rheometer, in which the inner cylinder rotates at a constant speed, and the outer cylinder is stationary. A critical rotational speed exists due to existence of yield stress. If rotation speed exceeds the critical value, all fluid is fully sheared between the concentric cylinders. Plug flow exists only when rotation speed is less than the critical value. The effects of radius ratio and Bingham number are discussed. The rheometer with radius ratio very close to unity is discussed as a limiting case, and the result confirms previous research. Formulas for calibration are derived using Least Squares and perturbation methods for all values of radius ratio, based on measured rotation speed and torque. Two sets of experimental data are used for verification. The validation shows that the formulas derived here yield reasonable and accurate estimates of rheological parameters.

The Shapes of Teeth of Circular Saw Blade and Their Influence on its Critical Rotational Speed

The main problems during cutting with circular saw blade are inaccurate cut, low quality of surface, high level of noise. These adverse effects are related to oscillation of circular saw blade. This oscillation cause adverse effects not only on workpiece but also on tool. In some case the circular saw blade reaches the value of critical rotational speed which leads to its instability and cause the oscillation of blade which may leads to destruction of tool. So the reduction of the amplitude of oscillation is essential for removing the adverse effects. This paper deals about influence of shapes of teeth as a type of modification that has positive effect oncritical rotational speed of circular saw blade. The parameters of studied models of circular saw blade were 42 number of teeth and the height of teeth with slice from sintered carbide was 14 mm. The variable parameter was the ratio between surface of teeth and surface of teeth gap. In this study was used computer software Creo Parametric 1.0 for obtaining natural frequencies of studied models. This software uses in analysis finite element method (FEM). There were done some steps to idealize the models. For calculating static and dynamics natural frequencies of modelswere used modal analysis. The critical rotational speed was calculated from obtained results by Creo Parametric 1.0 and compared on 5 models of tool.

Numerical Study of the Laminar Flow Past a Rotating Square Cylinder at Low Spinning Rates

The fluid dynamic interaction between a uniform free stream flow and the rotation induced flow from a sharp edged body is numerically investigated. A two-dimensional (2D) finite volume based computation is performed in this regard to simulate the laminar fluid flow around a rotating square cylinder in an unconfined medium. Body fitted grid system along with moving boundaries is used to obtain the numerical solution of the incompressible Navier–Stokes equations. The Reynolds number based on the free stream flow is kept in the range 10≤Re≤200 with a dimensionless rotational speed of the cylinder in the range 0≤Ω≤5. At low Re=10, the flow field remains steady irrespective of the rotational speed. For 50≤Re≤200, regular low frequency Kármán vortex shedding (VS) is observed up to a critical rate of rotation (Ωcr). Beyond Ωcr, the global flow shows steady nature, although high frequency oscillations in the aerodynamic coefficients are present. The rotating circular cylinder also shows likewise degeneration of Kármán VS at some critical rotational speed. However, significant differences can be seen at higher rotation. Such fluid dynamic transport around a spinning square in an unconfined free stream flow is reported for the first time.