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In this paper, to help reduce the squeal noise produced during the braking of urban railway vehicles, the shape of the disc brake pad was investigated to relieve contact stress. To analyze the disc brake system to identify the source of the squeal noise, a finite element model of the disc brake system was used, including the peripheral brake parts to increase accuracy. A complex eigenvalue analysis was performed to predict squeal noise generation. Verification was carried out using domestic urban railway field test results to confirm the accuracy of the analysis model. A pad shape that relieves contact stress is proposed to reduce squeal noise produced by nonuniform contact between the disc and pad. The results of this study can be utilized for future studies on squeal noise reduction.

This paper presents a CFD analysis of three types of axial-flow magnesium-based automotive cooling fans. The numerical modeling was conducted for geometrically modified fan designs: one with no-beads, the second one with beads at the suction-side of the fan namely reverse-beads fan, and the third one with beads installed at the pressure-side of the fan namely forward-beads fan. The effect of geometric modifications of the fan blades on the volumetric flow rate, fan efficiency, and energy efficiency was investigated using Reynolds-averaged Navier-Stokes (RANS) equations following the multiple reference frame methodology. The fan with no-beads was fabricated using 3D printing technology and tested to measure the flow velocity. Subsequently, the fans with beads along with the no-beads fan designs were numerically analyzed. The volumetric flow rate, fan efficiency, and energy efficiency were quantified as a function of fan rotating speed. The results show that the reverse-beads fan produced a relatively more volumetric flow rate and energy-efficient compared to the forward-beads fan. Moreover, to further improve the performance of the reverse-beads fan, the location and size of the bead structure were varied along the radial direction of the fan blade. The optimized reverse-beads fan significantly improves the fan performance.

The unsteady RANS equations for a two-dimensional hydrofoil were solved using ANSYS Fluent to model and simulate the hydrofoil at a constant Reynolds number, Re, of 2 × 105 and a fixed reduced frequency, f*, of 0.14. The simulations were performed by varying parameters, such as the number of deflectors N, tilt angle of the deflectors β, and vertical spacing of the deflectors J* = J/c, to determine the effect of the upstream deflector’s position on the hydrofoil’s performance. The results demonstrated that the deflector was effective at redirecting the separated flow away from the edges, which was then amplified downstream before colliding with the leading edge of the oscillating hydrofoil to increase power extraction. The performance of the oscillating hydrofoil was highly reliant on all three studied parameters. The hydrofoil with two deflectors (N = 2) displayed marginally superior power extraction capability compared to the hydrofoil with a single deflector (N = 1). Furthermore, the hydrofoil with the rightward inclined deflector at a low tilt angle (−5° ≥ β ≥ −10°) exhibited relatively better power extraction performance than the others. The best deflector design increased the hydrofoil’s cycle-averaged power coefficient by approximately 32% compared to a hydrofoil without a deflector. The vortex structures revealed that the flow evolution and power extraction performance were dependent on the size, robustness, and growth rate of the leading edge vortex (LEV) as well as the timing of LEV separation. The power extraction efficiency of an oscillating hydrofoil increased in the mid downstroke and upstroke due to the formation of a more robust LEV when the hydrofoil–deflector interaction was advantageous, but it dropped in the wing reversal due to the early separation of the LEV when the hydrofoil–deflector interaction was counterproductive.

The thrust production of an oscillating wing in the low Reynolds number regime (75 ≤ Re ≤ 1000) was investigated via threedimensional numerical simulations, primarily focusing on exploring the effects of aspect ratio AR (3 ≤ AR ≤ 10) and heave-pitch phase difference φ (0° ≤ φ ≤ 360°) on thrust production and propulsion efficiency ηp by tracing the tip vortices. The propulsion characteristics were observed to be strongly dependent on φ and Re but weakly dependent on AR. The oscillating wing produces positive thrust + Cx for 67.5° ≤ φ ≤ 135°. The maximum + Cx is produced at φ = 112° due to the flow features namely ‘constructive wake deflection’ and ‘mild flow separation during stroke reversal’. The coherent vortex structures reveal that the horseshoe ring HSR formed in each stroke aids in producing positive thrust via momentum change. The shape and size of the HSR are affected by the AR of wing. The shape of HSR is nearly circular at low AR, whereas it is a rounded rectangle at high AR. The HSR is noticed to transport the flow of high magnitude in uvelocity when Re = 450 and 1000, that will increase the positive thrust.

An understanding of the mechanism of aircore phenomenon during draining is very important. In this study, numerical simulations were conducted for different pressurized and suction pressure water tanks, as well as for different drain port diameters, to explain and validate the proposed aircore mechanism. It was found that increasing the pressure at the top surface of the tank results in suppression of the aircore, whereas an increase in the suction pressure at the drain port outlet enhances the development of the aircore. For different drain port diameters, it was observed that the duration of the aircore during draining decreases with a decrease in the drain port diameter, and that the aircore is suppressed for a very small drain port diameter.

Unmanned rotorcraft represents a new paradigm in agricultural activities. Rotor-blade design to improve lift performance was necessitated because payload-mounted flights suffer from a lack of lift. A prototype of rotor blade, comprising the V2008B airfoil, was assessed on an agricultural rotorcraft. The lift corresponding to the collective pitch angle (CPA) and rotor speed was measured on field and compared with a base-line blade. Measurements demonstrated that the prototype blade could sustain a maximum payload of 589 N, resulting in a total lift of 1256 N. Thus, an increase of 10.5 % in total lift was accomplished, compared with a base-line of 1137 N. Simulation also indicated that total lift equals 1269 N at CPA = 10°, approximately 1.0 % greater than the experimental lift. However, a practical spray payload would be reduced due to the ground effect and uncertainty, existing during an anchored field experiment. The ground effect from the experimental operation close to the ground would reduce 10 % of the total lift, resulting in 1138 N for hovering. Furthermore, uncertainty existed in stick control inputs and local wind conditions, resulting in fluctuations of rotor speed and payload. The standard deviation of net lift was ±45.33 N; therefore, the minimum net lift of the low envelope assessed from the uncertainty analysis would be 426 N.

In the present study, numerical simulations are performed to explore the significance of elytron-hindwing interaction in the forward flying Coleopteran beetle. The study investigates the effects of hindwing stroke amplitude (A/c) and advance ratio (J), (which is defined as the ratio of the incoming air velocity to the wing flapping velocity), on the aerodynamic forces. The wing kinematics of a Coleopteran beetle is constructed by using a combination of translation and rotation motion. The elytron is modeled by using a cambered airfoil that mimics the real geometry of the beetle wing, and the hindwing is modeled by using an elliptical profile. The results indicate that the beetle cruises with a constant velocity at approximately J = 0.3 in the tandem wing arrangement. It is observed that the angle of the net force vector relative to the stroke plane tilts systematically according to the flying speed. The influence of vortex structures on the beetle aerodynamic forces is analyzed. The elytron-hindwing interaction is found to be beneficial to the vertical force generation of hindwing as well as for the elytron when J > 0.0. The vortices interaction is observed during the downstroke period, and the leading edge vortex (LEV) of the elytron is captured by LEV of the hindwing that enhances the total vertical force. During the upstroke translation phase, the combined trailing edge vortex of elytron interacts/merges with the LEV of the hindwing and increases the horizontal force.

High global production of medium-density fiberboard (MDF) in recent years could generate an equal quantity of waste MDF at the end of its service life, requiring recycling of waste MDF instead of l...

This study pertains to the design optimization of a four-blade ceiling fan to enhance air circulation and energy efficiency. The sweep angle of the blade profile is nonlinear. The design of experiment (DOE) computational fluid dynamics (CFD) and response surface method (RSM) methods were used in parallel to find the optimal design solution. The design variables considered were inboard angle of attack, outboard angle of attack, blade sweep, and tip-chord length. Numerical simulations were conducted using steady state Reynolds-averaged Navier–Stokes (RANS) equations and the Spalart–Allmaras turbulence model. The baseline results were validated through experimental data. Subsequently, the DOE method was employed to generate the blade design which reduce the number of simulations without losing the influence of different geometric parameter interactions. The response variables studied were volume flow rate, mass flow rate, torque, and energy efficiency. The simulations exhibited that flow pattern has a distinct feature and is further classified into three groups. In the end, the optimal blade design was identified using response surface methodology (RSM).

Purpose The purpose of this study is to numerically investigate the influence of corner radius on the flow around two square cylinders in tandem arrangements at a Reynolds number of 100. Design/methodology/approach Six models of square cylinders with corner radii R/D = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5 (where R denotes the corner radius and D denotes the characteristic dimension of the body) were studied using an immersed boundary-lattice Boltzmann method, and the results were compared with those obtained using a two-dimensional unsteady finite volume method. The cylinders were mounted in a tandem configuration (1.5 ≤ L/D ≤ 10 where L denotes the in-line separation between the cylinder centers). The simulated models were quantitatively compared to the aerodynamic force coefficients and Strouhal number. Furthermore, qualitative analysis is presented in the form of flow streamlines and vorticity contours. Findings The R/D and L/D values were varied to observe the variation in the flow characteristics in the gap and wake regions. The numerical results revealed two different regimes over the spacing range. The drag force on the downstream cylinder was negative for all corner radii values when the cylinders were placed at L/D = 3.0 (a single-body system). Subsequently, a sudden increase was observed in the aerodynamic forces (drag and lift) when L/D increased. A different gap value was identified in the transformation from a single-body to a two-body system for different corner radii. To verify the single-body system, a simulation was carried out with a single cylinder having a longitudinal geometric dimension equal to the tandem arrangement (L/D + D). Furthermore, in a single-body regime, the total drag of a tandem cylinder was less than that of a single cylinder, thus demonstrating the benefits of using tandem structures. A significant reduction in the aerodynamic forces and drag force was achieved by rounding the sharp corners and placing the cylinders in close proximity. An appropriate configuration of the tandem cylinders with a rounded corner of R/D = 0.4 and 0.5 at L/D = 3.0 and the range is enhanced to L/D = 4.0 for 0.0 ≤ R/D < 0.4 to achieve adequate drag reduction. Originality/value To the best of the author’s knowledge, there is a paucity of studies examining the effect of corner radius on bluff bodies arranged in a tandem configuration.

Understanding the air-core development during the draining of liquid from a cylindrical tank is of particular interest because this phenomenon has multiple engineering applications. In this study, experiments are performed for draining water of different temperatures from a cylindrical tank. Results show that the air-core generation and disappearance during draining depend on the temperature of the water in the tank, in which the total draining time increases with the water temperature. A correlation is proposed to predict the water height with time during draining. A numerical study is then performed for some of the temperature cases. Numerical and correlation results show a good agreement with the experimental data. Findings show that viscosity plays an important role behind the mechanism of air-core generation and disappearance phenomena.

There is growing interest in unmanned aerial pesticide application, which is a new farming paradigm aimed at reducing labor and improving production stability. To alleviate the difficulties being experienced by operators and pilots, researchers are focusing on the lack of lift and are trying to enhance lift by improving rotor airfoil. In this study, with the objective of enhancing the rotor performance of agricultural unmanned helicopters, the performance of basic airfoils was evaluated in a wind tunnel and via computational fluid dynamics simulation. The lift and power characteristics of rotor blades were also evaluated. As airfoil design steps to improve the lift of unmanned helicopter, the characteristics of lift, drag, and power were analyzed via wind tunnel tests for the 400 mm section models of two airfoils, specifically a thick airfoil (V1505A) with blunt nose and a thin airfoil (V2008B) with drooping nose. The V1505A airfoil is appropriate for the inboard region, which requires stable aerodynamics at a high angle of attack. On the other hand, the V2008B airfoil is ideal for the outboard region of the rotor because it has a relatively high dynamic efficiency. Therefore, it is expected that a transitional airfoil blade with a negative twist angle can solve the problems of unmanned aerial pesticide application.

Purpose The paper aims to study the influence of rounded corners on the flow-induced oscillation of a square cylinder that is free to oscillate in two degrees of freedom. Design/methodology/approach The finite volume code in conjunction with the moving mesh scheme was implemented via a user-defined function to carry out the computations in two dimensions. The Reynolds number (Re) chosen for the present study is fixed at 100, and the frequency ratio, Fr = fs/fn (where fs is the vortex shedding frequency and fn is the natural frequency of cylinder) is used as a varying parameter. The computational model was validated for flow past a stationary cylinder with R/D = 0 and 0.5, and the results showed good agreement with the literature. Findings The aerodynamic characteristics, amplitude response, trajectories of cylinder motion and vortex shedding modes are obtained by conducting a series of simulations under different frequency ratios of the cylinder. It was found that the minimum transverse amplitude, drag force and lift force obtained for a naturally oscillating square cylinder are quite different when compared with a stationary and forced oscillating cylinder, where the maximum drag and lift forces were observed for a square cylinder and a minimum around R/D = 0.2 was observed. Originality/value The present work identified the significant effect of the varying frequency ratio and R/D on the VIV modes of the cylinder. It was observed that the cylinder wake exhibits the (2S) vortex shedding mode for R/D = 0 to 0.2 at all Fr, whereas the C (2S) mode appeared for R/D > 0.2 at Fr = 1.1.

The importance of using Agriculture unmanned helicopters (AUHs), especially for spraying pesticides and fertilizers on any terrain type to ensure crop yields, has been recently acknowledged. Apart from flying these helicopters at a super-low altitude and low speed, using an efficient and optimum rotor blade ensures a uniform and deep penetration of pesticide and fertilizers over a specified area. Accordingly, this work attempts to optimize the rotor blade of an AUH by using coupling statistics and several numerical techniques, including design of experiments, response surface method, and computational fluid dynamics. The experiments are designed using the central composite design method and by selecting the geometric variables that affect the aerodynamic performance of the rotor blade, including the root chord, tip chord, and angle of attack. The angle at the root and tip is optimized in order for the resulting twist to produce a uniform blade loading, achieve maximum lift, and minimize the required hover power. The required aerodynamic forces and limited availability of engine power are identified as constraints. The blade is optimized only when the helicopter is hovering at a persistent rotational speed, and the hover efficiency of the rotor blade with an optimal twist distribution is significantly higher than the baseline.

Draining of liquids through cylindrical tanks is a very common phenomenon and has many applications. Understanding the aircore formation and its growth during draining has attracted appreciable interest in the literature. In this study, water draining through cylindrical tanks was studied using experimental and numerical techniques. Eight different initial heights of water in the tank between 310 and 450 mm with a 20-mm increment were tested in each experiment. The numerical study shows good agreement with the experimental data and promotes understanding of the generation and disappearance of an aircore during draining. For the different initial water heights, the experiments were performed with and without initial rotation of the tank. It is found that in the experiments without initial tank rotation, the drain time of water increases with increasing initial height. On the other hand, the drain time remains almost the same for all initial heights tested with initial tank rotation. The small variation in the drain time even when the initial water level is reduced is explained by the aircore duration during draining. Also, the mechanism of generation and disappearance of aircore is proposed with the help of numerical results.

This paper includes parametric study and optimization of non-linear ceiling fan blades by combining the techniques of Design of Experiments (DOE), Response Surface Methods (RSM) and Computational Fluid Dynamics (CFD). Specifically, the nonlinear (elliptical) planform shape of ceiling fan blade is investigated in conjunction with blade tip width, root and tip angle of attack. Sixteen cases are designed for three blade ceiling fan using two level full factorial model. The flow field is modeled using Reynolds-Averaged-Navier-Stokes approach. The performance variables used to formulate a multi-objective optimization problem are volumetric flow rate, torque and energy efficiency. Response Surface Method is used to generate the optimized design for non-linear ceiling fan blade profile. The results reveal that the interactions between the design variables play a significant role in determining the performance. It is concluded that the nonlinear forward sweep has a moderate effect on response parameters.

An air core is the vortex flow generated when rotating liquid in a tank drains into a narrow drain port. In various industrial areas, the air core often causes adverse effects, such as unwanted air entrainment or a reduced drain flow rate. The air core phenomenon has largely been simulated with a 2-D axisymmetric flow assumption. In this study, a 3-D numerical simulation of the liquid draining from a cylindrical tank was conducted. The results were compared with previous experimental and 2-D simulation results. Based on the present 3-D simulation results, as an air core generation mechanism, the interaction between the axially and circumferentially rotating vortex structures was suggested. Additionally, 3-D flow structures such as toroidal Taylor vortex rings and spiral waves on free surfaces, which could not be obtained in 2-D simulations, were successfully reproduced.

Purpose – The purpose of this paper is to numerically investigate the influence of corner radius on flow past a square cylinder at a Reynolds number 500. Design/methodology/approach – Six models were studied, for R/D=0 (square cylinder), 0.1, 0.2, 0.3, 0.4, and 0.5 (circular cylinder), where R is the corner radius and D is the characteristic dimension of the body. The transient two-dimensional (2D) laminar and large eddy simulations (LES) models were employed using finite volume code. The Strouhal number, mean drag coefficient (CD), and root mean square (RMS) value of lift coefficient (CL,RMS), for different R/D values, were computed and compared with experimental and other numerical results. Findings – The computational results showed good agreement with previously published results for a Reynolds number, Re=500. It was found that the corner effect on a square cylinder greatly influences the flow characteristics around the cylinder. Results indicate that, as the corner radius ratio, R/D, increases, the Strouhal number increases rapidly for R/D=0-0.2, and then gradually rises between R/D=0.2 and 0.5. The minimum values of the mean drag coefficient and the RMS value of lift coefficient were found around R/D=0.2, which is verified by the time averaged streamwise velocity deficit profile. Originality/value – On the basis of the numerical results, it is concluded that rounded corners on a square cylinder are useful in reducing the drag and lift forces generated behind a cylinder. Finally, it is suggested that with a rounded corner ratio of around R/D=0.2, the drag and oscillation of the cylinder can be greatly reduced, as compared to circular and square cylinders.

In this study, the near wake characteristics of transversely oscillating square-section cylinders with different corner radii were investigated using the particle image velocimetry (PIV) technique in a water channel with turbulence intensity of 6.5%. Five models with r/B = 0, 0.1, 0.2, 0.3, and 0.5, respectively (where r and B represent the corner radius and the characteristic dimension of the body, respectively), were studied, with the body oscillation limited to that under the lock-in condition. Corner radius was found to significantly influence the characteristics of the flow around the bodies, both under stationary and oscillating conditions. The results indicate that the Strouhal number and vortex strength of the flow increase and decrease, respectively, with an increase in the r/B ratio. The spacing between two rows of vortices (b) as well as that between consecutive vortices in a row (a) was also found to decrease with the increase in the corner radius. The b/a ratio was found to be nearly independent of the r/B ratio and body oscillation.

The motor-driven water pump boiler for a water circulating mattress generates noise and vibration as it supplies a large water flow rate. A non-pump boiler can reduce such noise and vibration, however, the water circulation flow rate becomes lesser than that in motor-driven water pump boilers, and a large temperature deviation occurs between the inlet and the outlet of the mattress. In this research, a new non-pump boiler for water circulating mattress is developed and its performance is experimentally validated and compared with the existing non-pump boilers. The experimental results show that temperature response time is improved and temperature deviation is reduced.

In this study, two proposals for the wall heating preconverter of an MCFC are numerically studied to resolve hot temperature generation near the wall by the low thermal conductivity of the catalyst. The numerical results show that the inserted porous cupper plates on the catalyst evidently improve heat transfer and realize more uniform reforming in the preconverter. The calculated results for the preconverter with a circumference empty space of catalyst located at center, 1/2 and 4/5 from center line are compared. The circumference empty space located at 1/2 position shows better results than other cases, but the positive effect on the uniform reforming process is less than in the case of inserted cupper porous plates on the catalyst.

Key Words: CFD(전산유체역학), Preconverter(프리컨버터), Stream Reforming Reaction(수증기개질반응),Heat Transfer(열전달), Fuel Conversion(연료전환율)초록: 본연구에서는비상시전기공급용MCFC 프리커버터의천연가스(메탄)로부터수소의생산량을증가시키는경우를수치적으로해석하였다. 상용코드를사용하였으며촉매는다공성매질로시뮬레이션하였다. 3가지주요화학반응인수증기개질반응(SR), 수성가스전환(WGS) 및직접수증기개질반응(DSR)은사용자부프로그램을사용하여해석하였다. 프리컨버터에서10%의연료전환율을얻기위해요구되는추가열량을벽면을통해공급하게되면프리컨버터의벽면부근에서만매우불균일한온도분포와화학반응이일어나는것으로분석되었다. 이와같은현상은매우작은열전도율을갖는다공성매질의촉매와흡열반응으로설명되어질수있다. 해석결과프리컨버터의길이가짧은경우가보다균일한연료전환율을보여주며, 촉매의유지보수면에도길이가짧은경우가유리함을보여주었다.Abstract: In this study, a preconverter of an MCFC for an emergency electric power supplier is numerically simulated toincrease the hydrogen production from natural gas (methane). A commercial code is used to simulate a porous catalystwith a user subroutine to model three dominant chemical reactions—steam reforming, water-gas shift, and direct steamreforming. To achieve a fuel conversion rate of 10% in the preconverter, the required external heat flux is supplied fromthe outer wall of the preconverter. The calculated results show that the temperature distribution and chemical reaction areextremely nonuniform near the wall of the preconverter. These phenomena can be explained by the low heat conductivityof the porous catalyst and the endothermic reforming reaction. The calculated results indicate that the use of a compact-sizepreconverter makes the chemical reaction more uniform and provides many advantages for catalyst maintenance.

An air core is generated during draining through an axisymmetrically placed circular orifice after rotating a cylindrical tank filled with a liquid. If an air core is generated, the draining flow rate decreases and the draining time increases. In this study, the process of the formation of the air core and internal flow characteristics in a cylindrical tank are studied by numerical methods. Several methods are used in the analysis, and the results are compared with experimental results to obtain the appropriate scheme. Axial, radial, and swirl velocity profiles on a variety of heights are shown graphically, and the internal flow structure is analyzed from the velocity profiles, the vector plot, and the stream function distribution.

When draining takes place through an axially located drain port in a cylindrical tank without any prevent, a vortex with an air core occurs. In this study, semi spherical concave and convex meshes with different size inner hole are used to find the air core can suppress. The study is carried out with different values of inner hole of mesh and different install direction of semi spherical mesh using PIV and measured velocity distribution. By providing a mesh, the air core can be prevented, even if the ratio of inner hole of mesh and diameter of cylinder is around 0.66. The experimental results show that a convex mesh type is more effective to suppress the air core generation than a concave mesh type.

In this paper, various operating parameters of stream reforming process from methane in stream reformer and preconverter for MCFC is studied by numerical method. Commercial code is used to simulated the porous catalyst with user subroutine to model three dominant chemical reactions which are Stream Reforming(SR), Water-Gas Shift(WGS), and Direct Stram Reforming(DSR). The hydrogen production is tested with different wall temperature and different reactor shapes. The calculated results of the concentration of hydrogen in stream reformer are very well consistent with experimental results. This numerical study gives the design reactor wall temperature condition and size of reactor to satisfy the required fuel conversion.

The flow field in square tanks with various corner roundings is studied to investigate drain flow characteristics. An attempt is made to understand the mechanism of flow field responsible for vortex suppression by the different radius of rounding at the corner. For this purpose, flow visualization studies using particle image velocimetry are employed to determine the flow patterns in a square tank. Results are obtained for no draining and with draining experiments. The flow field is visualized both in horizontal and vertical planes. The results reveal that the secondary vortices formed at the corners are responsible for vortex suppression.

The vortexing phenomenon that occurs in a cylindrical container is studied using PIV. The influence of the vane-type suppressors which prevent the vortex formation is investigated. An attempt has been made to understand the mechanism that is responsible for vortex suppressing. There is a strong updraft generated due to the suppressors which leads to annihilation of vorticity which appears to be responsible for vortex suppression.

In this paper, the reverse flow in a square duct with an obstruction at the front (which is a square plate), is investigated using particle image velocimetry (PIV). The gap g between the obstruction and the entry to the duct was systematically varied, and it was found that maximum reverse flow occurs around a g/w value of 0.75. The velocity vectors, vorticity plots, and other details described indicate that the flow field is different compared with the two-dimensional channel case.

The near wake flow field features of transversely oscillating square section cylinders with different corner radii were studied in an attempt to assess the influence of corner radius. The investigation was performed by using particle image velocimetry (PIV) technique in a water channel with a turbulence intensity of 6.5%. Five models were studied with r/B=0, 0.1, 0.2, 0.3 and 0.5 (r is the corner radius and B is the characteristic dimension of the body), and the body oscillation was limited to lock-in condition (at fe/fo=1.0; fe is the excitation frequency and fo is the vortex shedding frequency from a stationary cylinder at the same Re). The corner radius was found to significantly influence the flow features around the bodies. Except for r/B=0.5, for all the other cases of r/B ratios, cycle-to cycle variation in the mode of vortex shedding was observed in the case of oscillating cylinders inducing highly non-linear wake characteristics. Apart from variation in the shedding mode, changes in shedding cycle timing were also observed for sharp and rounded square cylinders. The hgher the r/B ratio, shedding in the near wake was found to be more uniform (lesser variation in shedding cycle timings). Another admissible shedding mechanism is newly identified to operate in the near wake of oscillating cylinders now being called as the ‘passive shedding’ mechanism. Results indicate that increasing the corner radius suppresses the possible instabilities of the cylinder.

In this paper, the flow-induced oscillation of a prismatic body, viz., a square section cylinder (test cylinder) under interference conditions is analysed considering it as representing a typical building structure. The analysis is carried out using a data-mining tool called 'Decision Tree' mainly in view of assessing the safety of the structure (test cylinder) with respect to the vibratory amplitude. To achieve this aim, wind tunnel studies have been conducted on the vibratory response of the test cylinder when it is vibrating in the vicinity of another square cylinder (interfering cylinder) which is placed at various locations relative to the test cylinder. The amplitude data thus obtained is suitably classified to carry out the safety analysis. All the data gathered pertains to at a single value of reduced velocity (10.0). Experiments have been carried out for various size ratios (b/B) of the test cylinder (upstream structure) and the interfering cylinder with values of 0.5, 1.0, 1.5 and 2.0. The results indicate that, for certain combinations of the parameters - relative position (L/B, T/B) and size ratio (b/B), the upstream structure could vibrate with high amplitudes making the structural environment 'critical' (unsafe). In practical situations (such as in the case of tall buildings), the critical combinations of these parameters could be identified and eliminated for ensuring structural safety. Parametric combinations ensuring safe structural condition are also identified. Decision Tree also brings out the order of importance of various parameters influencing the interference excitation of the structure (test cylinder); L/B is shown to be the most influencing parameter. The results also show that, for L/B>3.0, there is a higher possibility for the structure to become unsafe when compared to the conditions at L/B=

Wind tunnel experiments were conducted to study the interference excitation of a square section cylinder (test cylinder) and the results are reported in this paper. The study was carried out at some specific relative positions identified between the test cylinder (side dimension B) and the interfering cylinder (side dimension b) so that the latter is never upstream of the former. Experiments were carried out for the b/B ratios of 0.5, 1.0, 1.5 & 2.0. In this paper, emphasis is laid on bringing out the influence of b/B ratio on the vibratory response of the test cylinder, considering a few interference positions. The results show that at a particular relative position, the magnitude of vibrations and the response trend of the test cylinder are markedly influenced by the b/B ratio. Under certain combinations of b/B ratio, relative position and reduced velocity, test cylinder vibrations are considerably magnified and in certain other combinations they are suppressed. Flow visualization results are provided in an attempt to bring out the influence of b/B ratio and also to explain the observed vibratory features of the test cylinder.

This paper presents the results of an analysis of flow-induced oscillations of a square section cylinder under interference conditions using a data-mining tool called ‘decision tree’. The interference effects were studied at some specific relative positions identified. Experiments have been carried out for various relative dimensions or size ratios ( b / B ) of the test cylinder and the interfering cylinder with values of 0.5, 1.0, 1.5 and 2.0. It has been found that the parameters reduced velocity ( U / fB ), relative position ( L / B , T / B ) and size ratio ( b / B ) influence the flow-induced oscillation of the cylinder quite significantly. In practical situations, very often, critical combinations of these parameters leading to objectionable vibratory amplitudes may occur and, hence, they need to be identified and eliminated. It is here the application of ‘decision tree’ found to be significantly helpful. Hence, in this paper, emphasis is laid on the effectiveness of ‘decision tree’ in analysing the flow-induced vibration data and consequently arriving at the safest as well as the critical conditions. The results show that, for safer design conditions, reduced velocity should be lower than a threshold value. It has been also found that relative position is playing only a lesser significant role when compared to reduced velocity and size ratio. The results further show that critical conditions are very likely to occur at high reduced velocities, for size ratios greater than one.

Reverse flow occurs in a channel when there is an obstruction at the entry. However it has been shown recently that reverse flow can be realized without an obstruction, by staggering the sides of the channel and placing it at an angle of attack to the oncoming flow. In this study the latter flow is computationally investigated. Studies have been carried out for different widths (gap between the two walls forming the channel), and at an angle of attack of 30. The results have captured all the essential features of this complex phenomenon and show the time dependent pumping mechanism which leads to the occurrence of reverse flow.

Draining of liquids through cylindrical tanks is very common phenomena. An interesting but undesirable Aircore is generated during draining process. Therefore understanding of air core formation and its growth is of quite interest in literature. In present study, water draining through cylindrical tanks is studied by experimental techniques. Rotational Froude number is varied based on different initial heights of water in the cylinder. Spatial and temporal variation of critical height and critical time against experiments performed is reported in paper. From comparison of critical height ratio against Froude numbers under consideration, it is found that air core generates slower for lower Froude numbers. Therefore, for higher initial heights of liquid column in the tank, the Aircore generates later as compared to lower initial liquid height case, and this seems to be the reason for the same drain time for all the initial water heights being used in the study. In order to validate the concept, further experiments are performed without initial swirl of tank. Thus causing no Aircore to generate during draining. It is found that with decreasing height the drain time decreases. This validate the concept that early Aircore generation was the major reason behind same drain times with different volumes of water in the cylinder.Copyright © 2015 by ASME

Dynamic flow characteristics of a counter-flow vortex tube is investigated using hot-wire and piezoelectric transducer (PZT) measurements. The experimental study is conducted over a range of cold air outlet ratios (Y=0.3, 0.5, 0.7, and 1.0) and inlet pressure 0.15 MPa. Temperatures are measured at the cold air outlet and along the vortex tube wall. Hot-wire is located at cold outlet and PZT is installed at inner vortex tube by mounting at throttle valve. The cold outlet temperature results show that the swirl flow of vortex tube is not axisymmetric. The hot-wire and PZT results show that there exist two distinct kinds of frequency, low frequency periodic fluctuations and high frequency periodic fluctuations. It is found that the low frequency fluctuation is consistent with the Helmholtz frequency and the high frequency fluctuation is strongly related with precession oscillation.

This paper explores the possibility of improving the power density of a solid oxide fuel cell (SOFC). A three-dimensional computational model (CFD-ACE package), with the relevant sub-models was used for the study. The performance of the SOFC was examined with a thin wall, which splits the inlet section and runs up to half the length of the flow channels. The results obtained with this (thin-walled) geometry were consistently better than those obtained with plain geometry (without the thin wall). The polarization characteristics of the thin-walled geometry indicated that the maximum power density obtained was 1.18 W cm −2 at an efficiency of around 60%. The corresponding values of maximum power density and the efficiency at which it was obtained for a plain geometry were 0.88 W cm −2 and 50%, respectively. The enhanced performance of the thin-walled geometry was attributed to a better distribution of the reactants along the length of the SOFC. Studies were also conducted to verify the performance of the thin-walled geometry over a wide range of inlet mass flow rates. They revealed a superior performance of the thin-walled geometry compared to the plain geometry. At lower inlet mass flow rates, the difference between the two in performance was small, but at higher inlet mass flow rates the difference in performance was significant.

The present investigation deals with the study of the internal flow phenomena of the counter flow type vortex tube using experimental testing and numerical simulation. Visualization was carried out using the surface tracing method, injecting dye on the vortex tube wall using a needle. Vortex tube is made of acrylic to visualize the surface particle tracing and the input air pressure was varied from 0.1 MPa to 0.3 MPa. The experimentally visualized results on the tube show that there is an apparent sudden changing of the trajectory on the vortex tube wall which was observed in every experimental test case. This may indicate the stagnation position of the vortex flow. The visualized stagnation position moves towards the vortex generator with increase in cold flow ratio and input pressure. Three-dimensional computational study is also conducted to obtain more detailed flow information in the vortex tube. Calculated total pressure, static pressure and total temperature distributions in the vortex tube were in good agreement with the experimental data. The computational particle trace on the vortex tube wall is very similar to that observed in experiments.

The present study proposes a modified temperature-dependent non-Newtonian viscosity model and investigates the flow characteristics and heat transfer enhancement of the viscoelastic non-Newtonian fluid in a 2:1 rectangular duct. The combined effects of temperature dependent viscosity, buoyancy, and secondary flow caused by the second normal stress difference are considered. Calculated Nusselt numbers by the modified temperature-dependent viscosity model give good agreement with the experimental results. The heat transfer enhancement of viscoelastic fluid in a rectangular duct is highly dependent on the secondary flow caused by the magnitude of second normal stress difference.

It is known that reverse flow (i.e., flow in the direction opposite to the free stream direction) occurs when an obstruction is placed near the entry to a channel (referred to as the test channel), kept inside another wider channel. The present investigation is focused on realizing a reverse flow in the test channel without an obstruction placed at the entry. Experiments in the water channel have been carried out along with flow visualization. The initial investigation revealed that reverse flow even in the absence of an obstruction would occur in a situation where the two walls, forming the channel have a stagger with respect to each other and are kept at an angle of attack. Studies have been carried out for different widths (i.e., gaps between the two walls forming the channel), stagger (i.e., perpendicular distance between the leading edges of the side walls), and angles of attack. It is found that both the stagger and the angle of attack are needed for reverse flow to occur. The critical angle of attack at which the reverse flow begins depends on the stagger and channel width. Copyright � 2006 Begell House, Inc.