Theoretical and experimental investigations of low Mach number turbulent cavity flows

Theoretical and experimental investigations are conducted for rectangular cavities of varying sizes in low Mach number turbulent flows. Emphasis is put on the characterization of the generation of self-sustained oscillations in order to develop methods of active control applied to the aeroacoustics of cavity flows. A linearized stability analysis for low Mach number flows is proposed in which the interface of the cavity is modeled by a vorticity layer. Subsequently, the cavity flow is investigated experimentally in a subsonic wind tunnel, using pressure measurements and a phase-locked particle image velocimetry system. Experimental results indicate that the oscillation process is governed by convective waves, with no definite influence of convected vortical structures. The good agreement between the experimental data and the predictions given by the model allows the identification of the oscillations of the cavity interface via the parameters issued from the theoretical analysis.List of symbols c speed of sound, m/s - f frequency, Hz - G Greens function - h displacement of the vorticity layer, m - K_R Rayleigh conductivity of the aperture, m - k₀ acoustic wavenumber, rad/m - k,n, Rossiter formula parameters - M Mach number of the freestream - pressure, Pa - Q volume flux, m³/s - Re_L Reynolds number Re_L=UL/ - Re_x1 Reynolds number Re_x1=Ux₁/ - Re Reynolds number Re=U/ - S frequency based Strouhal number - T period, s - t time, s - U,U,U^± freestream velocity, m/s - v velocity, m/s - W,L,D model cavity dimensions, m - w,l,d analytical cavity dimensions, m - x,y Cartesian coordinates, m - boundary-layer thickness, m - vorticity thickness, m - * boundary-layer displacement thickness, m - ,^± velocity potential, m²/s - acoustic wavelength, m - kinematic viscosity, m²/s - boundary-layer momentum thickness, m - ₀ density, kg/m³ - pulsation based Strouhal number - angular frequency, rad/s - vorticity, s ^–1 - , non-dimensional coordinates x₁,y₁ - non-dimensional displacement h     

Numerical and experimental investigations of micromechanical processes during wire sawing

In the following paper the mechanisms of the slurry-based wire sawing process at micro level are studied by numerical simulations. For the simulation a new approach in simulating the wire sawing process is presented. A discrete element method (DEM) with polyhedral particles is used to simulate the movement of the abrasive particles as well as the wire during the process. The results are verified by direct observations of the sawing channel of an experimental setup. The presented numerical model is applied for a detailed study of the influence of different process parameters.     

Theoretical and experimental investigations of wall adaptation control in wind tunnel and hybrid wind tunnel testing

The hybrid wind tunnel principle is an economical alternative to classical wind tunnels. Wall adaptation tests are reported which are performed in a small scale arrangement duplicating original kinematic relations. A new method for controlling the quality of wall adaptation is presented which is based on the pressure distribution at the rigid wall. This procedure may also be applied for wall adaptation in conventional wind tunnel technique.The experimental investigations reported here have been carried out by the following students in the course of undergraduate work: Ch. Bauer, C. Schultes, Th. Reimer and U. Walter. I am very grateful for their great care accomplished contributions.     

Theoretical and experimental investigations on the formation of air core in a swirl spray atomizing nozzle

Theoretical and experimental studies have been made to investigate the variations of air core diameter, the most important hydrodynamic picture inside a swirl nozzle, with the pertinent guiding parameters like injection condition expressed as the Reynolds number at inlet to the nozzle and the geometrical dimensions of the nozzle, namely, the length and diameter of the swirl chamber, angle of spin chamber and the orifice diameter. The theoretical relations have been established through an approximated analytical solution of the hydrodynamics of flow of a viscous incompressible fluid in a swirl nozzle. A series of experiments have been carried out to support and compare the theoretical results. Finally, it has been recognized that for any nozzle, the air core diameter becomes a direct function of Reynolds number Re _i at inlet to the nozzle only at its lower range and then remains constant. Amongst the nozzle geometrics, the ratio of orifice to swirl chamber diameter D ₂/D ₁ has got the most predominant effect on the air core diameter. An increase in the ratio of orifice to swirl chamber diameter D ₂/D ₁, and in the spin chamber angle 2 and a decrease in the swirl chamber length to diameter ratio L ₁/D ₁ increase the ratio of air core to orifice diameter and vice versa.Nomenclature A _E Area of tangential inlet ports of the nozzle - A ₂ Area of the orifice - a Air core radius - D ₁ Swirl chamber diameter - D ₂ Orifice diameter - d ₂ Air core diameter - E A nondimensional parameter defined by equation (14) - E _R A nondimensional parameter defined by equation (33) - L ₁ Length of the swirl chamber - P Static pressure - P _b Back pressure of the nozzle - Q Volume flow rate - R Radius vector or the longitudinal co-ordinate with respect to spherical co-ordinate system (figure 3) - R ₁ Radius of the swirl chamber - R ₂ Radius of the orifice - Re _i Reynolds number at inlet to the nozzle - R _z Radius of the nozzle at any section - r Radial distance from the nozzle axis - U Longitudinal component of velocity with respect to spherical co-ordinate system (figure 3) - V Component of velocity in the axial plane perpendicular to R as defined in (figure 3) - V _r Radial velocity component - V _z Axial velocity component - V _Ø Tangential velocity component - Average tangential velocity at inlet to the nozzle - w Component of velocity perpendicular to axial plane with respect to the spherical co-ordinate as defined in figure 3 - z Distance along the nozzle axis from its inlet plane - Half of the spin chamber angle - Boundary layer thickness - ₂ Boundary layer thickness at the orifice - Angle which a radius vector according to the system of spherical coordinates (figure 3) makes with the nozzle axis - Dynamic viscosity - Kinematic viscosity - Density - Ø Running co-ordinate in the azimuthal direction with respect to the cylindrical polar co-ordinate system as shown in figure 3 - Circulation constant     

Improved experimental tracking techniques for validating discrete element method simulations of tumbling mills

We report on further developments in the three-dimensional tracking of a particle deep within the tumbling ball charge of an experimental mill. The experimental X-ray program employing the use of bi-planar X-ray angiography now includes the tracking of a typical 6 mm bulk charge particle in three dimensions with a spatial resolution that is accurate to within 0.15 mm. The improved experimental tracking techniques presented were developed for the purpose of generating accurate three-dimensional particle trajectory data against which to validate a numerical method for the simulation of discrete media, namely the discrete element method (DEM). These improvements are complimented with techniques for comparing charge profiles between numerical DEM simulations and three-dimensional experimental trajectory data.     

Theoretical analysis and experimental study of Coriolis mass flow sensor sensitivity

The measuring tube is the core sensitive unit of the Coriolis mass flow sensor. Its design parameters directly influence natural frequency and sensitivity, such as shape and structure dimensions. In this study, we obtained under concentrated force the equivalent elastic coefficient of the measuring tube by adopting static analysis and calculating static deflection curves, including the respective U-shape, slightly curved, and straight tubes. We then obtained the resonant frequency from the second-order vibration equation. Additionally, the maximum sensitivity and position coordinates were obtained by calculating the torsional displacement curve of the measuring tube under the distribution of Coriolis force during a rated flow. Sensor models with different measuring tube shapes were designed by applying this theoretical analysis. Calibration tests for sensors were performed using a static gravimetric method. Theoretical analysis and test results show that the resonant frequency and sensitivity of the sensors calculated by applying static mechanical analysis and Coriolis distributing force align with the experimental results, thereby proving the validity of the theoretical method. Furthermore, the proposed method simultaneously obtained the relation curve of the measuring tube structure dimensions and natural frequency and sensitivity. It therefore provides theoretical evidence for the sensor design and detector installation position.     

Theoretical and numerical investigations on confined plasticity in micropillars

Multiscale dislocation dynamic simulations are systematically carried out to reveal the dislocation mechanism controlling the confined plasticity in coated micropillar. It is found that the operation of single arm source (SAS) controls the plasticity in coated micropillar and a modified operation stress equation of SAS is built based on the simulation results. The back stress induced by the coating contributes most to the operation stress and is found to linearly depend on the ‘trapped dislocation’ density. This linear relation is verified by comparing with the solution of the current higher-order crystal plasticity theory and is used to determine the material parameters in the continuum back stress model. Furthermore, based on the linear back stress model and considering the stochastic distribution of SAS, a theoretical model is established to predict the upper and lower bound of stress–strain curve in the coated micropillars, which agrees well with that obtained in the dislocation dynamic simulation.     

回转窑多粒径颗粒流动与偏析的DEM模拟与实验研究

为明晰回转窑内颗粒的运动行为及偏析机理,以绿豆、黄豆和黑豆为颗粒介质,依次对3种装填顺序下的颗粒流动过程进行离散元模拟与实验研究,以颗粒质量分数和平均粒度为判据,对颗粒偏析进行评价。结果表明,回转窑内颗粒流动区可分为自由滚落区、渗流呆滞区以及窑壁携带区,自由滚落区颗粒流速最大,而渗流呆滞区流速最小。窑内颗粒沿轴向输运过程发生径向偏析,形成夹层结构,小颗粒受渗流作用在渗流呆滞区中心形成内核,大粒径和中等粒径颗粒集中在自由滚落区和窑壁携带区。窑内颗粒力链分布不均匀,强力链分布于近窑壁区,弱力链分布于自由滚落区和渗流呆滞区,且渗流呆滞区力链细而密集。当窑头附近不同粒径颗粒存在轴向速度差时,颗粒在轴向发生掺混,并产生径向偏析。     

空间异型双曲面钢屋盖缺陷稳定性分析及试验研究

南通体育会展中心钢屋盖为空间异型双曲面,结构高跨比和矢跨比均较小,稳定性分析是其设计中的一个关键问题。本文在体育馆缩尺模型试验基础上,对其钢屋盖结构进行了几何非线性和双非线性稳定分析,分别采用实测缺陷法、一致缺陷模态法、改进随机缺陷法考虑结点位置偏差缺陷的影响。结果表明：实测缺陷法双非线性分析结果是评估体育馆屋盖结构实际安全性的重要依据;一致模态法的临界荷载概率可靠度较低。通过改进随机缺陷法,对该屋盖结构的稳定性能有了比较全面的认识,并定量分析了设计临界荷载和一致模态法分析的临界荷载的可靠性。     

Analytical,numerical and experimental investigations of architectural sandwich panels

Architectural sandwich panels with thin-walled cold-formed steel facings and rigid foamed insulating core are becoming more and more popular as enclosures for system buildings. In this paper, the structural behavior, including flexural stresses/deflections, flexural wrinkling, axial stability, thermal stresses and vibration, is presented, summarizing more than a decade of research. Methods used are analytical (boundaryvalued approaches), numerical (finite-strip, finite-layer, finite prism approaches) and experimental (full-scale testings). Key equations are formulated, and results by different methods are compared.     

Numerical and experimental investigations of a rotating nonlinear energy sink

In this work, passive nonlinear targeted energy transfer (TET) is addressed by numerically and experimentally investigating a lightweight rotating nonlinear energy sink (NES) which is coupled to a primary two-degree-of-freedom linear oscillator through an essentially nonlinear (i.e., non-linearizable) inertial nonlinearity. It is found that the rotating NES passively absorbs and rapidly dissipates a considerable portion of impulse energy initially induced in the primary oscillator. The parameters of the rotating NES are optimized numerically for optimal performance under intermediate and strong loads. The fundamental mechanism for effective TET to the NES is the excitation of its rotational nonlinear mode, since its oscillatory mode dissipates far less energy. This involves a highly energetic and intense resonance capture of the transient nonlinear dynamics at the lowest modal frequency of the primary system; this is studied in detail by constructing an appropriate frequency–energy plot. A series of experimental tests is then performed to validate the theoretical predictions. Based on the obtained numerical and experimental results, the performance of the rotating NES is found to be comparable to other current translational NES designs; however, the proposed rotating device is less complicated and more compact than current types of NESs.     

Theoretical and experimental investigations of the flow of a viscous fluid near the line of intersection of a cylindrical surface and a flat surface

Flow along a corner was investigated at large Reynolds numbers in, for example, [1–3]. The present author [4] considered flow in the neighborhood of a corner formed by the intersection of a plane and a concave cylindrical surface, the main attention being devoted to the formation of the three-dimensional boundary layer on the plane near the corner. It was shown that the curvature of one of the intersecting surfaces changes the flow pattern qualitatively. In the present paper, we report an investigation of the formation of the flow on a concave cylindrical surface near such a corner and consider how the flow is rearranged in the neighborhood of a corner in, for example, a channel of rectangular cross section that has an initial straight section and then a bend with a discontinuity of the curvature of the line of intersection of the concave and flat sides of the channel. The results are given of some experimental investigations of flow near the line of intersection of a flat wall and a curved (concave and convex) wall at a bend in a rectangular channel.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 1, pp. 64–68, January–February, 1983.I thank G. M. Bam-Zelikovich for constant interest in the work and A. I. Ruban for a number of extremely helpful comments.     

Interval analysis method and convex models for impulsive response of structures with uncertain-but-bounded external loads

Two non-probabilistic, set-theoretical methods for determining the maximum and minimum impulsive responses of structures to uncertain-but-bounded impulses are presented. They are, respectively, based on the theories of interval mathematics and convex models. The uncertain-but-bounded impulses are assumed to be a convex set, hyper-rectangle or ellipsoid. For the two non-probabilistic methods, less prior information is required about the uncertain nature of impulses than the probabilistic model. Comparisons between the interval analysis method and the convex model, which are developed as an anti-optimization problem of finding the least favorable impulsive response and the most favorable impulsive response, are made through mathematical analyses and numerical calculations. The results of this study indicate that under the condition of the interval vector being determined from an ellipsoid containing the uncertain impulses, the width of the impulsive responses predicted by the interval analysis method is larger than that by the convex model; under the condition of the ellipsoid being determined from an interval vector containing the uncertain impulses, the width of the interval impulsive responses obtained by the interval analysis method is smaller than that by the convex model.The project supported by the National Outstanding Youth Science Foundation of China (10425208), the National Natural Science Foundation of China and Institute of Engineering Physics of China (10376002) The English text was polished by Keren Wang.     

Numerical and experimental investigations of bistable beam snapping using distributed Laplace force

We report a study of an elastic buckled beam undergoing a contactless magnetic actuation of Laplace type. The beam model is based on the elastica beam theory including the beam extensibility. The Laplace force is produced by an electric current travelling along the beam placed in a magnetic induction. The magnitude of the electric current is the control parameter and by increasing the electric current the beam switches from one stable state to the other one for a given beam end-shortening. The main purpose of the study is to investigate the bistable response, more precisely, the diagram of the electric current as function of the midpoint vertical displacement of the beam according to the magnet location along the elastic beam. The model equations are established and they are numerically solved using an algorithm developed for nonlinear boundary value problem. A second part of the study is devoted to experimental validation of the model and comparisons with the results extracted from the numerical solutions to the model equations. Especially, the comparisons ascertain with good accuracy the approach of the proposed bista-ble beam model. In addition, the influence of the model parameters on the bistable response is clearly identified.

     

Theoretical and numerical investigations of TAP experiments: new approaches for variable pressure conditions

Temporal analysis of products (“TAP”, see Gleaves et al. in Catal Rev Sci Eng 30:49, 1988) is a valuable tool for characterisation of porous catalytic structures. Established TAP-modelling requires a spatially constant diffusion coefficient and neglect convective flows, which is only valid in Knudsen diffusion regime. A new theoretical model is developed for estimating the number of molecules per pulse to stay in Knudsen diffusion regime under any conditions and at any time. Moreover a new methodology for generating a full three-dimensional geometrical representation of beds is presented and used for numerical simulations. In computational fluid dynamics software (ANSYS CFX^® version 14) a transient diffusive transport equation with time-dependent inlet boundary conditions is solved. Three different pellet diameters were investigated with 1E+18 molecules per pulse, which is higher than the limit from the theoretical calculation (about 1E+15). From this results, the distance from inlet can be calculated where the theoretical pressure limit (Kn = 2) is obtained, i.e., from this point to the end of reactor, Knudsen regime can be assumed.     

Theoretical and experimental vibration analysis of an oblique space frame

This paper has the general objectives of relating analytical and experimental techniques for analysis of indeterminate spatial frames under dynamic loading. The model used has been made as general as possible to explore validity for nonstereotyped configurations. A highly redundant oblique four-bar space frame was selected having a lowest natural frequency of 42.1 cps. Recent success of the finite-element-matrix method and progress in the field of nonlinear optimization provides a rational basis for the synthesis of space frames; however, the validity of the discretization, both for strength-stiffness analysis and dynamic analysis, has not been explored for this type of configuration. The flexibility influence coefficients, the natural frequencies and the steady-state vibration amplitudes were experimentally determined and compared with theoretical values. Influence coefficients had an “error” of between four and 10 percent; the six lowest natural frequencies were in agreement within 15 percent when rotary inertia was considered. Steady-state amplitudes were in good agreement at frequencies not too close to resonance.     

Theoretical and experimental study of an enhanced nonlinear energy sink

Nonlinear Dynamics - Based on theoretical and experimental investigations, this paper proposes a nonlinear energy sink (NES) with piecewise linear springs to enhance vibration suppression effects....