Effect Of End Plates Research Articles

Nonlinear Aerodynamic Modeling of Cascade Fins And Delta-Wing Aircraft Model

The paper presents the modeling of the nonlinear longitudinal aerodynamics associated with the cascade fins and scale-down model of a delta-wing aircraft at high angles of attack. The Kirchhoff’s steady-state stall model was used to model the stall characteristics and the Maximum Likelihood (ML) method was used to estimate the stall characteristic parameters. The cascade fin models with a rectangular and an airfoil (NACA-0012) cross-section were used to generate the variation of lift coefficient with angle of attack. The wind tunnel data pertaining to the cascade fin models were generated by varying the gap-to-chord ratios with and without end plates. The effect of end plates and the gap-to-chord ratio on the stall characteristics and the parameter estimation was analysed. The estimation results were compared to the reference results. In addition, the application of the Kirchhoffs steady-stall model to the scale-down model of a delta-wing aircraft has also been presented. The analysis pertaining to the cascade fins can be utilized as a basis for an initial design of cascade fins for guided missiles with desirable stall characteristics.

Effects of end plates on vibro-acoustic responses of conical and cylindrical shells

A unified semi-analytic model is developed to study effects of end plates on vibro-acoustic characteristics of conical and cylindrical shells. The Flügge shell theory and power series method are combined to establish the structural model, while the boundary integral method for acoustic problems of axisymmetric bodies is employed to develop the acoustic model. By utilizing continuity conditions between structural and acoustic models, the vibro-acoustic governing equation is readily achieved. Rapid convergence of the developed model is discussed, and high accuracy and efficiency of present method are verified with the ones in the literature and calculated by finite element-boundary element method. Furthermore, the coupling effect between end plates and external fluid, contributions of end plates to vibro-acoustic responses and the effect of thickness of end plates are discussed. Results reveal that the coupling effect between end plates and external fluid is remarkable for cylindrical shells under axial forces or conical shells under both axial and radial forces. Simultaneously, contributions of end plates to vibro-acoustic responses are significant, and the variation of thickness of end plates apparently affects vibro-acoustic responses of the closed conical and cylindrical shells.

End Plate Effects on the Performance of PEMFCs During Cold Start Process

The efficient, fast, and reliable cold start of polymer electrolyte membrane fuel cells is one of the major challenges for their commercialization. In this paper a segmented single cell is used to simulate the end plate effects of the stack and to investigate how the effects work. The results demonstrate that the end cells in the stack have the lowest performance, the reasons of which include the lowest temperature of the cells themselves, and probably also the ice blocking in part area inside the MEA, or in the channels, or in both together. In order to mitigate or even to eliminate the influence of the ice formation in the end cells, the temperature of the end plates should be increased to −10 °C or above when the liquid water is generated. A high inlet gas flow rate facilitates the discharge of supercooled water and is conducive to successful cold start.

A quantitative analysis of the effect of end plate of fully-grouted bolts on the global stability of tunnel

Among the analyses of fully-grouted rock bolt in the rock mass, the effect of the end plate on the global stability of the tunnel has not been comprehensively reported. In this paper, a simplified numerical procedure for the interaction between the fully-grouted bolt and rock mass with consideration of the end plate is proposed. The rock-bolt interaction is considered at the initial and final states. At the initial state, immediately after the bolt is installed, a finite difference solution of the stresses and strains in the rock mass is proposed. At the final state, when the fictitious support pressure is negligible, another finite difference solution of the stresses along bolt as well as displacements in the rock mass is presented. To obtain the final results, a simplified iterative process is performed by repeating the finite difference solution at the final stage. The proposed procedure is verified by comparing with the commercially available finite difference software and field results. In the parametric studies, the effects of the end plate for the geological conditions with variation in rock mass quality, in-situ stress, shearing stiffness at the bolt-grout interface, and end plate stiffness are simultaneously investigated. The results indicate that, under the squeezing conditions, the failure mode of the bolt is influenced by the end plate stiffness; an optimum design for the shearing stiffness and end plate stiffness can be implemented in order to achieve an excellent supporting performance of the rock bolt.

Effect of end plates on transiting test for measuring the aerodynamic coefficient of structures using wind generated by a moving vehicle

This study aims to seek the optimum size and shape of end plates used for two-dimensional (2D) transiting tests. Experimental aerodynamic forces triangular cross-sectional bodies were measured both by using a dynamometric balance and by integrating the pressure distribution along the contour of the triangular cross-section are evaluated in this study to investigate the effect of end plates on the two-dimensional (2D) transiting test results. A total of 14 test conditions, in which the diameters of circular and square end plates D = 0, 3, 4, 6, 8, 9, 10 times of the depth of the testing body, were investigated. The turbulence intensity of the wind field in wind tunnel test, the turbulence intensity of the wind field measured in the transiting tests and the wind tunnel test was greatly affected by natural wind and road side obstacle by more than 4%. The variation of aerodynamic force coefficients and wind pressure coefficients of the model with the size of the end plates were analyzed. The ratio of the diameter of the end plates to the height of the model should be [4, 8] to ensure that the model is unaffected by the end plates.

Performance of heat pumps using pure and mixed refrigerants with maldistribution effects in plate heat exchanger evaporators

This paper presents a combined plate heat exchanger (PHE) - heat pump simulation framework for the evaluation of flow maldistribution in PHE evaporators and its effect on the cycle thermodynamic and economic performance. A case study of heat pump integration for waste heat recovery purposes in data centres was chosen to demonstrate the utilization of the simulation tool. The analyses were made for the pure fluids butane and propane, and for the zeotropic mixtures propylene/butane at (0.5,0.5) mass composition and CO2/dimethyl ether (DME) (0.2,0.8) as refrigerants. Both liquid/vapour maldistribution and the effect of end plates were considered in the heat exchanger models. Results show that butane is most sensitive to maldistribution, with a maximum Coefficient of Performance (COP) reduction of 5.9%, while propane experiences the lowest reduction of 2.5%. The different sensitivity of the working fluids to maldistribution was found to be related to the evaporator design, refrigerant pressure drop, and fluid properties. Last, the results of the economic analysis show that a higher specific cost of heat is obtained when considering maldistribution effects.

Effect of end plates on heat transfer of plate heat exchanger

Steady-state heat transfer data for single-phase (water) in both frame-and-plate (FPHE) and brazed plate heat exchangers (BPHE) are presented with various number of chevron plates in U-type flow arrangement. Analysis of the experimental results indicates that the end plates, instead of being adiabatic, function as fins due to the contact between adjacent plates. The experimental data is used to validate a thermal conduction model in ANSYS, which indicates that the end plates fin efficiency is a function of fluid convective heat transfer coefficient and conductive thermal resistance. In the FPHE, the pressing force of the frame may affect the contact thermal resistance, thus change the fin efficiency. In BPHE, the fin efficiency is much higher due to the larger contact area and higher conductivity of the brazing material. Although the effect of end plates is quickly diluted by the increased number of plates in real applications, it could be significant when plate number is small, as is often the case in laboratory settings for the development of heat transfer correlations.

Effects of the partially movable control fin with end plate of underwater vehicle

Underwater torpedo has control fin with very low aspect ratio due to launching from limited size of cylindrical torpedo tube. If the aspect ratio of control fin of underwater vehicle is very low three-dimensional flow around control fin largely reduces control forces. In this study, the end plate was applied to reduce the three-dimensional flow effects of partially movable control fin of underwater vehicle. Through numerical simulations the flow field around control fin was examined with and without end plate for different flap angles. The pressure, vorticity, lift and torque on the control fin were analyzed and compared to experiments. The comparison have shown a reasonable agreement between numerical and experimental results and the effect of end plate on a low aspect ratio control fin. When the end plate was attached to the movable control fin, the lift increased and the actuator shaft torque did not significantly change. As this means less consumption of the actuator shaft torque compared to the control fin that has the same control force, the inner actuator capacity can be reduced and energy consumption can be saved. Considering this, it is expected to be effectively applied to the control fin design of underwater vehicles such as torpedoes.

Effects of end plates with various shapes and sizes on helical Savonius wind turbines

We experimentally studied the effects of end plates with various shapes and sizes on the aerodynamic performance of helical Savonius wind turbines with twist angles of 180° and two semicircular buckets. To apply the blockage correction method and investigate the effect of end plate, four different helical Savonius wind turbines were tested at a subsonic open-circuit type wind tunnel. The adapted Maskell's blockage correction method suggested by Alexander was adopted for the wind turbine model installed in a closed test section of the subsonic wind tunnel. In order to clarify the end plate effect, power and torque coefficients were measured with various end plate shapes and areas. The use of both upper and lower end plates significantly increases the power coefficient by 36% compared with no end plates. We found that the Maskell's blockage correction method for straight Savonius wind turbines is applicable to helical Savonius wind turbines for small blockage ratios ranging from 3 to 8.3%. It was also observed that the power coefficient increases linearly in proportion to the area of the end plate.

Effects of End Plates on Performance of a Small Straight-Bladed Vertical Axis Wind Turbine

Effects of End Plates on Performance of a Small Straight-Bladed Vertical Axis Wind Turbine

Effects of End Plates and Blockage on Low-Reynolds-Number Flows Over Airfoils

Measurements on airfoils at low Reynolds numbers can have a strong dependence on the experimental setup as a result of the sensitivity of the transitioning separated shear layer that develops over the model. In this investigation, the effects of two aspects of the experimental setup, namely end plates and test-section blockage, on lowReynolds-numberairfoilexperiments areexploredthroughmeasurementsonaNACA0018airfoilmodelatachord Reynolds number of 100,000. The improvement in mean spanwise uniformity with end plates installed is quantified and demonstrates the importance of using end plates in two-dimensional airfoil experiments at low Reynolds numbers. Consistent with previous studies on the use of end plates on circular cylinder models, it is found that mean quantities measured on the center-span plane are least sensitive to end-plate spacing for spacings greater than roughly 7 times the projected model thickness. It is shown that the end-plate configuration affects vortex-shedding characteristics and disturbance amplification in the separated shear layer. Blockage effects are investigated by comparing measurements before andafter adaptive-wall test-section streamlining forsolid-blockage ratios between 4 and 8%. These blockage ratios are shown to cause errors in lift as high as 9% of the maximum lift and 3.5% in the wake vortex-shedding frequency. The results of this investigation can be used to estimate the effects of blockage on flow development in low-Reynolds-number airfoil experiments. It is demonstrated that a common blockagecorrectionmethodcanaccuratelycorrectliftmeasurementsformoderateblockagesinlow-Reynolds-numberairfoil experiments for conditions under which a separation bubble forms over the model.

Effects of End Plates on Reducing Checking of Pentachlorophenol-Treated Douglas-Fir Crossarms

Abstract The effect of metal end plates on reducing checking of pentachlorophenol-treated Douglas-fir crossarms was evaluated over 13 wet–dry cycles. Check development was variable over the first three to four cycles, and then steadily increased for both plated and nonplated ends of arms; however, both the number of checks and the maximum width of the checks were significantly lower on plated ends. The results suggest that end plating reduces the potential for deep check development in crossarms that could lead to early failure.

Numerical computation of end plate effect on Taylor vortices between rotating conical cylinders

End plate effect on Taylor vortices between rotating conical cylinders is studied by numerical method in this paper. We suppose that the inner cone rotates together with the end plate at the top and the outer one as well as the end plate at the bottom remains at rest. It is found that the instability sets in at a critical Reynolds number about Re = 80. Increase Re to about Re = 200 the first single clockwise vortex is formed near the top of the flow system. Further increase Re to about Re = 440 another clockwise vortex is formed under the first one. At about Re = 448 the third vortex is formed which rotates in counterclockwise direction between the first two vortices. With increasing of Re the process continues. Finally, a configuration is obtained with an odd number of vortices in the annulus at about Re = 700, which confirms the experimental observation. Moreover, the local extreme values of pressure and velocity are achieved at the adjacent lines between neighboring vortices or at the medium lines of vortices. The effect of gap size on vortices is also considered. It is shown that the number of vortices increases with decreasing of the gap size and the end plates play an important role in the parity of the number of the vortices.

Modelling of Cascade Fin Aerodynamics Near Stall using Kirchhoff's Steady-state Stall Model

Nonlinear longitudinal aerodynamics associated with cascade fins at high angles of attack near stall has been modelled using Kirchhoff's formulation. Grid fins are a relatively recent development in guided missile technology. In this paper, a new category of grid fins, nomenclatured as cascade fins, has been proposed. In cascade fin design, an appropriate selection of gap-to-chord ratio and the number of planar members lead to desired stall angle and acceptable overall lift coefficient, respectively. Kirchhoff's steady-state stall model has been validated on wind tunnel data generated for Cascade fins having rectangular airfoil cross-section. National Wind Tunnel Facility (NWTF) of IIT, Kanpur, was used to generate the wind tunnel data consisting of the variation of lift coefficient with angle of attack. The cascade fins were tested to generate the data by varying gap-to-chord ratio and number of planar fins. The cascade fins with rectangular cross-section were tested with and without end plates. Kirchhoff's steady-state stall model was applied to wind tunnel data of cascade fins for modelling flow separation point and maximum likelihood method was used to estimate the parameters characterising stall characteristics. The effects of end plates, variation of number of fins and gap-to-chord ratio on parameter estimation were also studied. It has been observed that Kirchhoff's steady-state stall model could advantageously be applied to model nonlinear aerodynamics associated with cascade fins at high angle of attack. Defence Science Journal, 2011, 61(2), pp.157-164 , DOI:http://dx.doi.org/10.14429/dsj.61.481

Effect of End Plates on the Performance of an Impulse Turbine for Wave Energy Conversion

The objective of this paper is to present the effect of end plate on the performances of the impulse turbine for wave energy conversion by experimental investigation. The experiments have been performed by model testing under steady flow conditions in the study. And then, the performances of the impulse turbine with end plates have been compared with those of the original impulse turbine, i.e., the impulse turbine without end plate. As a result, it is found that the characteristics of the impulse turbine with end plates are superior to those of the original impulse turbine. Furthermore, the effects of end plate size and penetration on the turbine characteristics have been clarified in the study.

Wells turbine with end plates for wave energy conversion

In order to improve the performance of the Wells turbine for wave energy conversion, the effect of end plate on the turbine characteristics has been investigated experimentally by model testing. As a result, it is found that the characteristics of the Wells turbine with end plates are superior to those of the original Wells turbine, i.e., the turbine without end plate and the characteristics are dependent on the size and position of end plate. Furthermore, by using a computational fluid dynamics (CFD), reason of the performance improvement of the turbine has been clarified and the effectiveness of the end plate has been demonstrated.

Effect of end plates on the performence of a wells turbine for wave energy conversion

In order to improve the performance of the Wells turbine for wave energy conversion, the effect of end plates on the turbine characteristics has been investigated experimentally by model testing under steady flow conditions. The end plate attached to the tip of the original rotor blade is slightly larger than the original blade profile. The characteristics of the Wells turbine with end plates have been compared with those of the original Wells turbine, i.e., the turbine without end plate. As a result, it has been concluded that the characteristics of the Wells turbine with end plates are superior to those of the original Wells turbine and the characteristics are dependent on the size and position of end plate. Furthermore, the effect of annular plate on the turbine performance, which encircles the turbine and is attached to the tip, was investigated as an additional experiment. However, its device was not effective in improving the turbine characteristics.

Electrical coupling in proton exchange membrane fuel cell stacks: mathematical and computational modelling

A mathematical model describing the effects of electrical coupling of proton exchange membrane unit fuel cells through shared bipolar plates is developed. Here, the unit cells are described by simple, steady-state, 1D models appropriate for straight reactant gas channel designs. A linear asymptotic version of the model is used to give analytic insight into the effect of the coupling, including estimates of the extent of the coupling in terms of the number of adjacent cells affected. An efficient numerical method is developed to solve the non-linear coupled system. Numerical results showing the effects on stack voltage due to a single cell with anomalous oxidant flow rate are given. The effects on stack performance due to end plate effects are also given. It is shown that electrical coupling has a significant effect on fuel cell performance.

2512 エンドプレートを有する波力発電用衝動タービン(S47-1 自然の流体エネルギー利用技術(波力,潮流),S47 自然の流体エネルギー利用技術)

In order to improve the performance of an impulse turbine with fixed guide vanes for wave energy conversion, the effect of end plate on the turbine characteristics has been investigated experimentally by model testing under steady flow conditions. And then, the characteristics of the impulse turbine with end plates have been compared with those of the original impulse turbine. As a result, it is found that the characteristics of the impulse turbine with end plates are superior to those of the original impulse turbine. Furthermore, the effects of end plate size and annular plate on the turbine characteristics have been clarified in the paper.

Pattern formation in weakly forced Taylor-Couette flow.

Low-inertia vortex formation and pattern selection are examined for axisymmetric Taylor-Couette flow with spatially modulated cylinders. The forcing is arbitrary but remains periodic. The modulation amplitude is assumed to be small, and a regular perturbation expansion is used to determine the flow field at small to moderately large Taylor numbers (below the critical threshold). It is found that the presence of a weak modulation leads unambiguously to the emergence of steady Taylor-vortex flow even at vanishingly small Taylor number. This situation is closely reminiscent of the effect of end plates, and the consequent onset of imperfect bifurcation. The vortex structure is found to have the same periodicity as the forcing when only one of the cylinders is modulated, or when the modulations are commensurate. For incommensurate modulations, the vortex pattern is quasiperiodic, with regions of almost purely azimuthal flow. When the counter-rotation speed of the outer cylinder increases, the original vortices are gradually replaced by new ones that end up spanning the entire gap width, and in turn break up into two vortices resulting in two rows of vortices commensurate with each cylinder modulation. It is also shown that, for any modulation amplitude, the forcing wave number that generates the most intense vortex flow for a given Taylor number varies monotonically with Ta, but always reaches the critical value predicted by linear stability analysis for straight cylinders, regardless of which cylinder is modulated.