On the Role of Higher-Order Evanescent Modes in End-Offset Inlet and End-Centered Outlet Elliptical Flow-Reversal Chamber Mufflers

This paper deals with the role of the higher-order evanescent modes generated at the area discontinuities in the acoustic attenuation characteristics of an elliptical end-chamber muffler with an end-offset inlet and end-centered outlet. It has been observed that with an increase in length, the muffler undergoes a transition from being acoustically short to acoustically long. Short end chambers and long end chambers are characterized by transverse plane waves and axial plane waves, respectively, in the low-frequency range. The nondimensional frequency limit k(0)(D-1/2) or k(0)R(0) as well as the chamber length to inlet/outlet pipe diameter ratio, i.e., L/d(0), up to which the muffler behaves like a short chamber and the corresponding limit beyond which the muffler is acoustically long are determined. The limits between which neither the transverse plane-wave model nor the conventional axial plane-wave model gives a satisfactory prediction have also been determined, the region being called the intermediate range. The end-correction expression for this muffler configuration in the acoustically long limit has been obtained using 3-D FEA carried on commercial software, covering most of the dimension range used in the design exercise. Development of a method of combining the transverse plane wave model with the axial plane wave model using the impedance Z] matrix is another noteworthy contribution of this work.

High-temperature kinetics of the reaction between CN and hydrocarbons using a novel high-enthalpy flow tube

More than 70 molecules of varied nature have been identified in the envelopes of carbon-rich stars through their spectral fingerprints in the microwave or far infrared regions. Many of them are carbon chain molecules and radicals, and a significant number are unique to the circumstellar medium. The determination of relevant laboratory kinetics data is critical to keep up with the development of the high spectral and spatial resolution observations and of the refinement of chemical models. Neutralneutral reactions of the CN radical with unsaturated hydrocarbons could be a dominant route in the formation of cyanopolyynes, even at low temperatures and deserve a detailed laboratory investigation. The approach we have developed aims to bridge the temperature gap between resistively heated flow tubes and shock tubes. The present kinetic measurements are obtained using a new reactor combining a high-enthalpy source with a flow tube and a pulsed laser photolysislaser-induced fluorescence system to probe the undergoing chemical reactions. The high-enthalpy flow tube has been used to measure the rate constant of the reaction of the CN radical with propane (C3H8), propene (C3H6), allene (C3H4), 1,3-butadiene (1,3-C4H6), and 1-butyne (C4H6) over a temperature range extending from 300 to 1200 K. All studied reactions of CN with unsaturated hydrocarbons are rapid, with rate coefficients greater than 10-10 cm3 center dot molecule-1 center dot s-1 and exhibit slight negative temperature dependence above room temperature. (c) 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 753766, 2012

Microstructural Evolution of A356 Al Alloy During Flow Along a Cooling Slope

Cooling slope (CS) has been used in this study to prepare semi-solid slurry of A356 Al alloy, keeping in view of slurry generation on demand for Rheo-pressure die casting process. Understanding the physics of microstructure evolution during cooling slope slurry formation is important to satisfy the need of semi-sold slurry with desired shape, size and morphology of primary Al phase. Mixture of spherical and rosette shaped primary Al phase has been observed in the samples collected during melt flow through the slope as well as in the cast (mould) samples compared to that of dendritic shape, observed in case of conventionally cast A356 alloy. The liquid melt has been poured into the slope at 650 A degrees C temperature and during flow it falls below the liquidus temperature of the said alloy, which facilitates crystallization of alpha-Al crystals on the cooling slope wall. Crystal separation due to melt flow is found responsible for nearly spherical morphology of the primary Al phase.

Stability of developing film flow down an inclined surface

Film flows on inclined surfaces are often assumed to be of constant thickness, which ensures that the velocity profile is half-Poiseuille. It is shown here that by shallow water theory, only flows in a portion of Reynolds number-Froude number (Re-Fr) plane can asymptotically attain constant film thickness. In another portion on the plane, the constant thickness solution appears as an unstable fixed point, while in other regions the film thickness seems to asymptote to a positive slope. Our simulations of the Navier-Stokes equations confirm the predictions of shallow water theory at higher Froude numbers, but disagree with them at lower Froude numbers. We show that different regimes of film flow show completely different stability behaviour from that predicted earlier. Supercritical decelerating flows are shown to be always unstable, whereas accelerating flows become unstable below a certain Reynolds number for a given Froude number. Subcritical flows on the other hand are shown to be unstable above a certain Reynolds number. In some range of parameters, two solutions for the base flowexist, and the attached profile is found to be more stable. All flows except those with separation become more stable as they proceed downstream. (C) 2012 American Institute of Physics. http://dx.doi.org/10.1063/1.4758299]

A novel gas flow sensing application using piezoelectric ZnO thin films deposited on Phynox alloy

We report on the novel flow sensing application of piezoelectric ZnO thin film deposited on Phynox alloy sensing element. Characterization of piezoelectric ZnO films deposited on Phynox (Elgiloy) substrate at different RF powers is discussed. ZnO films deposited at RF power of 100W were found to have fine c-axis orientation, possesses excellent surface morphology with lower rms surface roughness of 1.87 nm and maximum d(31) coefficient value 4.7 pm V-1. The thin cantilever strip of Phynox alloy with ZnO film as a sensing layer for flow sensing has been tested for flow rates ranging from 2 to 18 L min(-1). A detailed theoretical analysis of the experimental set-up showing the relationship between output voltage and force at a particular flow rate has been discussed. The sensitivity of now sensing element is similar to 18 mV/(L min(-1)) and typical response time is of the order of 20 m s. The sensing element is calibrated using in-house developed testing set-up. (C) 2012 Elsevier B.V. All rights reserved.

Minimum power consumption for drag reduction on a circular cylinder by tangential surface motion

We investigate the effect of a prescribed tangential velocity on the drag force on a circular cylinder in a spanwise uniform cross flow. Using a combination of theoretical and numerical techniques we make an attempt at determining the optimal tangential velocity profiles which will reduce the drag force acting on the cylindrical body while minimizing the net power consumption characterized through a non-dimensional power loss coefficient (C-PL). A striking conclusion of our analysis is that the tangential velocity associated with the potential flow, which completely suppresses the drag force, is not optimal for both small and large, but finite Reynolds number. When inertial effects are negligible (R e << 1), theoretical analysis based on two-dimensional Oseen equations gives us the optimal tangential velocity profile which leads to energetically efficient drag reduction. Furthermore, in the limit of zero Reynolds number (Re -> 0), minimum power loss is achieved for a tangential velocity profile corresponding to a shear-free perfect slip boundary. At finite Re, results from numerical simulations indicate that perfect slip is not optimum and a further reduction in drag can be achieved for reduced power consumption. A gradual increase in the strength of a tangential velocity which involves only the first reflectionally symmetric mode leads to a monotonic reduction in drag and eventual thrust production. Simulations reveal the existence of an optimal strength for which the power consumption attains a minima. At a Reynolds number of 100, minimum value of the power loss coefficient (C-PL = 0.37) is obtained when the maximum in tangential surface velocity is about one and a half times the free stream uniform velocity corresponding to a percentage drag reduction of approximately 77 %; C-PL = 0.42 and 0.50 for perfect slip and potential flow cases, respectively. Our results suggest that potential flow tangential velocity enables energetically efficient propulsion at all Reynolds numbers but optimal drag reduction only for Re -> infinity. The two-dimensional strategy of reducing drag while minimizing net power consumption is shown to be effective in three dimensions via numerical simulation of flow past an infinite circular cylinder at a Reynolds number of 300. Finally a strategy of reducing drag, suitable for practical implementation and amenable to experimental testing, through piecewise constant tangential velocities distributed along the cylinder periphery is proposed and analysed.

Eulerian two-phase flow simulation and experimental validation of semisolid slurry generation process using cooling slope

Experimental and numerical studies of slurry generation using a cooling slope are presented in the paper. The slope having stainless steel body has been designed and constructed to produce semisolid A356 Al alloy slurry. The pouring temperature of molten metal, slope angle of the cooling slope and slope wall temperature were varied during the experiment. A multiphase numerical model, considering liquid metal and air, has been developed to simulate the liquid metal flow along the cooling channel using an Eulerian two-phase flow approach. Solid fraction evolution of the solidifying melt is tracked at different locations of the cooling channel following Schiel's equation. The continuity, momentum and energy equations are solved considering thin wall boundary condition approach. During solidification of the melt, based on the liquid fraction and latent heat of the alloy, temperature of the alloy is modified continuously by introducing a modified temperature recovery method. Numerical simulations has been carried out for semisolid slurry formation by varying the process parameters such as angle of the cooling slope, cooling slope wall temperature and melt superheat temperature, to understand the effect of process variables on cooling slope semisolid slurry generation process such as temperature distribution, velocity distribution and solid fraction of the solidifying melt. Experimental validation performed for some chosen cases reveals good agreement with the numerical simulations.

Numerical Investigation on Laminar Flow Due to Sudden Expansion Using Nanofluids

Laminar two-dimensional sudden expansion flow of different nanofluids is studied numerically. The governing equations are solved using stream function-vorticity method. The effect of volume fraction of the nanoparticles and type of nanoparticles on flow behaviour is examined and found significant impact. The flow response to Reynolds number in the presence of nanoparticles is examined. The presence of nanoparticles decreases the flow bifurcation Reynolds number. The size and the reattachment length of the bottom wall recirculation increase with increasing volume fraction and particle density. The effect of volume fraction and density of nanoparticles on friction factor is reported. The bottom wall recirculation strongly respond to the variation in volume faction and type of particles. However, weak response is observed for top wall recirculation.

Effect of substrate surface roughness on electric current induced flow of liquid metals

Electric current can induce long-range flow of liquid metals over a conducting substrate. This work reports on the effect of the substrate surface roughness on the liquid metal-front velocity during such a flow. Experiments were conducted by passing electric current through liquid gallium placed over similar to 170 nm thick, 500 mu m wide gold and platinum films of varying roughness. The ensuing flow, thus, resembles micro-fluidics behavior in an open-channel. The liquid-front velocity decreased linearly with the substrate surface roughness; this is attributed to the reduction in the effective electric field along the liquid metal-substrate interface with the substrate surface roughness. (C) 2013 American Institute of Physics. http://dx.doi.org/10.1063/1.4790182]

On the dynamic contact angle in simulation of impinging droplets with sharp interface methods

Effects of dynamic contact angle models on the flow dynamics of an impinging droplet in sharp interface simulations are presented in this article. In the considered finite element scheme, the free surface is tracked using the arbitrary Lagrangian-Eulerian approach. The contact angle is incorporated into the model by replacing the curvature with the Laplace-Beltrami operator and integration by parts. Further, the Navier-slip with friction boundary condition is used to avoid stress singularities at the contact line. Our study demonstrates that the contact angle models have almost no influence on the flow dynamics of the non-wetting droplets. In computations of the wetting and partially wetting droplets, different contact angle models induce different flow dynamics, especially during recoiling. It is shown that a large value for the slip number has to be used in computations of the wetting and partially wetting droplets in order to reduce the effects of the contact angle models. Among all models, the equilibrium model is simple and easy to implement. Further, the equilibrium model also incorporates the contact angle hysteresis. Thus, the equilibrium contact angle model is preferred in sharp interface numerical schemes.

A THREE-WHEELED MOBILE ROBOT FOR TRAVERSING UNEVEN TERRAIN WITHOUT SLIP: SIMULATION AND EXPERIMENTS

A wheeled mobile robot (WMR) can move on uneven terrains without slip if the wheels are allowed to tilt laterally. This paper deals with the analysis, design and experimentations with a WMR where the wheels can tilt laterally. The wheels of such a WMR must be equipped with two degrees of freedom suspension mechanism. A prototype three-wheeled mobile robot is fabricated with a two degree-of-freedom suspension mechanism. Simulations show that the three-wheeled mobile robot can traverse uneven terrains with very little slip and experiments with the prototype on a representative uneven terrain confirm that the slip is significantly reduced.

Effect of compressibility on the velocity gradient tensor at free shear flow boundaries

Analyses of the invariants of the velocity gradient ten- sor were performed on flow fields obtained by DNS of compressible plane mixing layers at convective Mach num- bers Mc=0:15 and 1.1. Joint pdfs of the 2nd and 3rd invariants were examined at turbulent/nonturbulent (T/NT) boundaries—defined as surfaces where the local vorticity first exceeds a threshold fraction of the maximum of the mean vorticity. By increasing the threshold from very small lev-els, the boundary points were moved closer into the turbulent region, and the effects on the pdfs of the invariants were ob-served. Generally, T/NT boundaries are in sheet-like regions at both Mach numbers. At the higher Mach number a distinct lobe appears in the joint pdf isolines which has not been ob-served/reported before. A connection to the delayed entrain-ment and reduced growth rate of the higher Mach number flow is proposed.

A Finite Element Method Based Approach for Evaluating the Sensitivity of Faraday-Type Electromagnetic Flow Meter for Liquid Sodium Flow

Faraday-type electromagnetic flow meters are employed for measuring the flow rate of liquid sodium in fast breeder reactors. The calibration of such flow meters, owing to the required elaborative arrangements is rather difficult. On the other hand, theoretical approach requires solution of two coupled electromagnetic partial differential equation with profile of the flow and applied magnetic field as the inputs. This is also quite involved due to the 3D nature of the problem. Alternatively, Galerkin finite element method based numerical solution is suggested in the literature as an attractive option for the required calibration. Based on the same, a computer code in Matlab platform has been developed in this work with both 20 and 27 node brick elements. The boundary conditions are correctly defined and several intermediate validation exercises are carried out. Finally it is shown that the sensitivities predicted by the code for flow meters of four different dimensions agrees well with the results given by analytical expression, thereby providing strong validation. Sensitivity for higher flow rates, for which analytical approach does not exist, is shown to decrease with increase in flow velocity.

Effects of two-wheelers on saturation flow at signalized intersections in developing countries

Two-wheelers (TW) constitute a major proportion of urban traffic in developing countries and therefore their effect on the saturation flow at signalized intersections could be substantial. This paper attempts to study and analyze the effect of two-wheelers on the saturation flow of signalized intersections by collecting data at a few signalized intersections in Bangalore, India. A strong correlation is observed between the measured saturation flow and the proportion of two-wheeler traffic, which suggest that two-wheelers have significant impact and should be considered in the capacity analysis of signalized intersections. In this paper, the effect of two-wheelers on saturation flow rate is incorporated in a previous model by calibrating and introducing a new adjustment factor for two-wheelers. Results show that saturation flow measured using the modified HCM equation is closer to observed saturation flow values.

A soluble-lead redox flow battery with corrugated graphite sheet and reticulated vitreous carbon as positive and negative current collectors

A soluble-lead redox flow battery with corrugated-graphite sheet and reticulated-vitreous carbon as positive and negative current collectors is assembled and performance tested. In the cell, electrolyte comprising of 1 center dot 5 M lead (II) methanesulfonate and 0 center dot 9 M methanesulfonic acid with sodium salt of lignosulfonic acid as additive is circulated through the reaction chamber at a flow rate of 50 ml min (-aEuro parts per thousand 1). During the charge cycle, pure lead (Pb) and lead dioxide (PbO2) from the soluble lead (II) species are electrodeposited onto the surface of the negative and positive current collectors, respectively. Both the electrodeposited materials are characterized by XRD, XPS and SEM. Phase purity of synthesized lead (II) methanesulfonate is unequivocally established by single crystal X-ray diffraction followed by profile refinements using high resolution powder data. During the discharge cycle, electrodeposited Pb and PbO2 are dissolved back into the electrolyte. Since lead ions are produced during oxidation and reduction at the negative and positive plates, respectively there is no risk of crossover during discharge cycle, preventing the possibility of lowering the overall efficiency of the cell. As the cell employs a common electrolyte, the need of employing a membrane is averted. It has been possible to achieve a capacity value of 114 mAh g (-aEuro parts per thousand 1) at a load current-density of 20 mA cm (-aEuro parts per thousand 2) with the cell at a faradaic efficiency of 95%. The cell is tested for 200 cycles with little loss in its capacity and efficiency.