• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.7 s.262
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• pp.628-634
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• 2007

The present study investigated the heat/mass transfer characteristics in an equilateral triangular channel simulating the leading edge cooling passage in gas turbine blade. Using naphthalene sublimation method and pressure measurement experiments, local mass (heat) transfer and pressure coefficients were obtained. The experiments were conducted with three rotating numbers between 0.0 and 0.1; two channel orientations of $0^{\circ}$ (model A) and $30^{\circ}$ (model B); the fixed Reynolds number of 10,000. The results showed that the channel rotation caused the heat transfer discrepancy between suction and pressure sides. Due to the secondary flow induced by Coriolis force, the high heat transfer appeared on the pressure side. When the channel orientation was $30^{\circ}$ (model B), the secondary flow caused the more uniform heat transfer distribution among leading edge and inner wall on pressure side than that of the model A.

• Journal of computational fluids engineering
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• v.13 no.1
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• pp.14-20
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• 2008

The flow characteristics around a rudder in open water condition is analyzed by the computational method. Reynolds averaged Navier-Stoke's equation is utilized for the computation. The computational hydrodynamic force coefficients are verified through comparing with the experimental results. The information of these flow characteristics is necessary to predict cavitation and maneuvering performances, to estimate steering gear capacitance, and to get the bending moment which is useful for the structural analysis. The pressure distribution, the three-dimensional flow separation, and the tip vortices are investigated. The pattern of the three-dimensional flow separation is analyzed utilizing a topological rule. The tip vortices are also investigated through a visualization technique.

• Journal of the Korea Institute of Military Science and Technology
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• v.17 no.1
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• pp.149-157
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• 2014

In this paper, we investigated the sensitivity of aerostatic force coefficients of multi-layer radom in the various wind speeds. The test was conducted in KOCED Wind Tunnel Center in Chonbuk National University, and wind speeds were in the range from 5 m/s to 26 m/s in order to determine the Reynolds number independence. The test results of present multi-layer radom were not affected by the Reynolds number, The maximum positive pressure coefficient was found to be 1.08 at the center of the front of the plane in angle of attack of 0 degree, the maximum negative pressure coefficient was -2.03 at the upper right corner in angle of attack of 120 degree, while maximum drag coefficient was 1.11 in angle of attack of 180 degree.

• Wind and Structures
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• v.29 no.4
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• pp.247-270
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• 2019

Wind-resistant design of existing cooling tower structures overlooks the impacts of rainfall. However, rainstorm will influence aerodynamic force on the tower surface directly. Under this circumstance, the structural response of the super-large cooling tower (SLCT) will become more complicated, and then the stability and safety of SLCT will receive significant impact. In this paper, surrounding wind fields of the world highest (210 m) cooling tower in Northwest China underthree typical wind velocities were simulated based on the wind-rain two-way coupling algorithm. Next, wind-rain coupling synchronous iteration calculations were conducted under 9 different wind speed-rainfall intensity combinations by adding the discrete phase model (DPM). On this basis, the influencing laws of different wind speed-rainfall intensity combinations on wind-driving rain, adhesive force of rain drops and rain pressure coefficients were discussed. The acting mechanisms of speed line, turbulence energy strength as well as running speed and trajectory of rain drops on structural surface in the wind-rain coupling field were disclosed. Moreover, the fitting formula of wind-rain coupling equivalent pressure coefficient of the cooling tower was proposed. A systematic contrast analysis on its 3D distribution pattern was carried out. Finally, coupling model of SLCT under different working conditions was constructed by combining the finite element method. Structural response, buckling stability and local stability of SLCT under different wind velocities and wind speed-rainfall intensity combinations were compared and analyzed. Major research conclusions can provide references to determine loads of similar SLCT accurately under extremely complicated working conditions.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.38 no.3
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• pp.234-240
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• 2002

The static stability of the otter board in relation to the angle of attack ($\alpha$) was studied analytically and experimentally from the moments of tensions and hydrodynamic force acting on it. Three flat plates of 0.5, 1.0, and 1.5 aspect ratios (λ) and four cambered plates of 5, 10, 15, and 20% camber ratios (CR) with the same aspect ratio (λ=1.5) were tested in a circulating water tank for measuring the hydrodynamic forces and moments relevant to the position of hydrodynamic center. And, center-of-pressure coefficients ($C_p$) and moment coefficients ($C_M$) of each plate as a function of the angle of attack were calculated for estimating the static stability from hydrodynamic forces. The obtained results are summarized as follows ； 1． When the angle of attack for otter board is changed from equilibrium for some reason, moments depending upon tensions of warp and sweep line always act in order to have the static stability, respectively. 2. Position of center-of-pressure of each flat plate moves from leading edge to center of plate with the increase of the angle of attack. It means that the moment of hydrodynamic force acting on flat plates also increases the static stability of plate. 3. With the increase of the angle of attack for cambered plates, the positions of center of-pressure move from trailing to leading edge, and then turn toward center of plate. As the camber ratios increase, the ranges of the angle of attack of the static un stability depending on moment of hydrodynamic force become wide.

• Wind and Structures
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• v.5 no.1
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• pp.49-60
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• 2002

This paper describes a simple method for evaluating the design wind loads for the structural frames of circular flat roofs with long spans. The dynamic response of several roof models were numerically analyzed in the time domain as well as in the frequency domain by using wind pressure data obtained from a wind tunnel experiment. The instantaneous displacement and bending moment of the roof were computed, and the maximum load effects were evaluated. The results indicate that the wind-induced oscillation of the roof is generally dominated by the first mode and the gust effect factor approach can be applied to the evaluation of the maximum load effects. That is, the design wind load can be represented by the time-averaged wind pressure multiplied by the gust effect factor for the first mode. Based on the experimental results for the first modal force, an empirical formula for the gust effect factor is provided as a function of the geometric and structural parameters of the roof and the turbulence intensity of the approach flow. The equivalent design pressure coefficients, which reproduce the maximum load effects, are also discussed. A simplified model of the pressure coefficient distribution is presented.

• Wind and Structures
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• v.15 no.6
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• pp.509-529
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• 2012

Traditionally, a quasi steady response concerning the aerodynamic force and moment coefficients acting on a flat plate while 'flying' through the air has been assumed. Such an assumption has enabled the flight paths of windborne debris to be predicted and an indication of its potential damage to be inferred. In order to investigate this assumption in detail, a series of physical and numerical simulations relating to flat plates subject to autorotation has been undertaken. The physical experiments have been carried out using a novel pressure acquisition technique which provides a description of the pressure distribution on a square plate which was allowed to auto-rotate at different speeds by modifying the velocity of the incoming flow. The current work has for the first time, enabled characteristic pressure signals on the surface of an auto-rotating flat plate to be attributed to vortex shedding.

• International Journal of Fluid Machinery and Systems
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• v.2 no.2
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• pp.147-155
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• 2009

Dynamic characteristics of the clearance flow between an axially oscillating rotational disk and a stationary disk were examined by experiments and computations based on a bulk flow model. In the case without pressure fluctuations at the inlet and outlet of the clearance, parallel and contracting flow paths had an effect to stabilize the axial oscillation of the rotating disk. The enlarged flow path had an effect to destabilize the axial oscillation due to the negative damping and stiffness for outward and inward flows, respectively. It was shown that the fluid force can be decomposed into the component caused by the inlet or outlet pressure fluctuation without the axial oscillation and that due to the axial oscillation without the inlet or outlet pressure fluctuation. A method to predict the stiffness and damping coefficients is proposed for general cases when the device is combined with an arbitrary flow system.

• Physical Therapy Rehabilitation Science
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• v.2 no.1
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• pp.31-38
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• 2013

Objective: To determine the efficacy and reliability of measuring direct current microcurrent applied through the skin to determine injury in the underlying tissues. Design: Case control study. Methods: First, microcurrent was measured as decreased blood flow induced hypoxia in healthy subjects. Next, reliability was assessed by measuring over ten days with set variations in pressure and distance between the electrodes. Finally, measurements over sprained ankle were compared to measurements over comparable uninjured areas on the same injured subject. Results: For the blood flow test phase, microcurrent significantly decreased an average of 17% after 5 minutes (p<0.05), remained decreased for 30 seconds, and returned to non-occlusive levels after 2 minutes of normal circulation. The results indicate that the microcurrent decrease was not due to blood flow, and most likely from hypoxic cellular damage. For the reliability phase, the coefficients of variation averaged 10.3% for the shoulder, 14.8% for the low back, and 29.1% for the knee. Changing distance 2.5 cm between the electrodes resulted in insignificant changes. Changes in pressure had some significant effect after an increase in force of 2.6 N, affirming the need for consistent pressure for measurement. For the injury test phase, a significant 69% decrease occurred comparing injured areas to the same area on the uninjured side, and a significant 74% occurred comparing injured and non-injured areas on the same limb. Conclusions: Microcurrent through the skin shows promise as an objective method of assessing a soft tissue injury by detecting damage likely due to hypoxia.

• Wind and Structures
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• v.32 no.3
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• pp.205-217
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• 2021

Cold regions with high air density and wind speed attract wind energy producers across the globe exhibiting its potential for wind exploitation. However, exposure of wind turbine blades to such cold conditions bring about devastating impacts like aerodynamic degradation, production loss and blade failures etc. A series of wind tunnel tests were performed to investigate the effect of icing on the aerodynamic properties of wind turbine blades. A baseline clean wing configuration along with four different ice accretion geometries were considered in this study. Aerodynamic force coefficients were obtained from the surface pressure measurements made over the test model using MPS4264 Simultaneous pressure scanner. 3D printed Ice templates featuring different ice geometries based on Icing Research Tunnel data is utilized. Aerodynamic characteristics of both the clean wing configuration and Ice accreted geometries were analysed over a wide range of angles of attack (α) ranging from 0° to 24° with an increment of 3° for three different Reynolds number in the order of 105. Results show a decrease in aerodynamic characteristics of the iced aerofoil when compared against the baseline clean wing configuration. The key flow field features such as point of separation, reattachment and formation of Laminar Separation Bubble (LSB) for different icing geometries and its influence on the aerodynamic characteristics are addressed. Additionally, attempts were made to understand the influence of Reynolds number on the iced-aerofoil aerodynamics.