• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.5
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• pp.30-38
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• 2006

A new calibration method for five-hole pressure probe is presented. This method provides accuracies better than those based on the traditional regression method. The calibration algorithm uses a single sector interpolation response surface calculated by comparing the regression curve fits with the actual calibration data. A five-hole pressure probe with hemispherical tip was fabricated and calibrated at Reynolds number of $4.11{\times}10^6$/m and flow angle of ${\pm}48$ degrees. Two data prediction models, the least-square regression and a single sector error interpolation, were evaluated. The comparison of these two calibration methods to a five-hole probe is described and discussed. An evaluation of the calibration accuracy is also given.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2002.11a
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• pp.440-447
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• 2002

This paper considerated about exact flow volume calculation method from factors having an influence on measurement and introduced in anesthesia ventilator realized spirometry system. System used differential pressure sensing method with factors, that is temperature, pressure, gas density, humidity and mucus etc. System optimized for low power system for mobile system. System composed analog interface part, signal processing part, display part. Analog interface part have differential pressure flow sensor and defferential pressure sensor. Signal processing part have AVR processor for low power system display part use serial port (RS232, SPT). so it display at pc monitor or send to anesthesia ventilator. System is stable by linearizing 2th characteristics of flow-differential pressure, auto correction of sensor. Noise reduced by algorithm with analog filter and digital processing. Small, light, low power system is good at mobile system and applied to patient in emergency or mobile. and, System is useful at anesthesia ventilator by using flow sensor.

• Structural Engineering and Mechanics
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• v.70 no.4
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• pp.479-497
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• 2019

In the current code design, the use of a uniform internal pressure coefficient of cooling towers as internal suction cannot reflect the 3D characteristics of flow field inside the tower body with different ventilation rate of shutters. Moreover, extreme weather such as heavy rain also has a direct impact on aerodynamic force on the internal surface and changes the turbulence effect of pulsating wind. In this study, the world's tallest cooling tower under construction, which stands 210m, is taken as the research object. The algorithm for two-way coupling between wind and rain is adopted. Simulation of wind field and raindrops is performed iteratively using continuous phase and discrete phase models, respectively, under the general principles of computational fluid dynamics (CFD). Firstly, the rule of influence of 9 combinations of wind speed and rainfall intensity on the volume of wind-driven rain, additional action force of raindrops and equivalent internal pressure coefficient of the tower body is analyzed. The combination of wind velocity and rainfall intensity that is most unfavorable to the cooling tower in terms of distribution of internal pressure coefficient is identified. On this basis, the wind/rain loads, distribution of aerodynamic force and working mechanism of internal pressures of the cooling tower under the most unfavorable working condition are compared between the four ventilation rates of shutters (0%, 15%, 30% and 100%). The results show that the amount of raindrops captured by the internal surface of the tower decreases as the wind velocity increases, and increases along with the rainfall intensity and ventilation rate of the shutters. The maximum value of rain-induced pressure coefficient is 0.013. The research findings lay the basis for determining the precise values of internal surface loads of cooling tower under extreme weather conditions.

• Journal of computational fluids engineering
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• v.13 no.4
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• pp.126-134
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• 2008

We developed a three dimensional Navier-Stokes code based on the level set method to simulate two phase flows with high density ratio. The Navier-Stokes equations with consideration of the surface tension effects are solved by using SIMPLE algorithm on a non-staggered grid. The present code is validated by simulating two test problems. First one is to simulate a rising bubble inside a cube. The thickness of the interface of the bubble is shown to affect the pressure distribution around the interface. As the thickness decreases, the pressure field around the interface becomes more oscillatory. As the bubble rises, a ring vortex is shown to form around the interface and the bubble eventually develops into an ellipsoidal shape. Merge of two bubbles inside a container is secondly tested to show the robustness of the present code for two phase flow simulation. Numerical results show stable and reliable behavior during the process of merging of two bubbles. The velocity and pressure fields around the interface of bubbles are shown oscillation free during the merging of two bubbles.

• International Journal of Aeronautical and Space Sciences
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• v.17 no.1
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• pp.29-36
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• 2016

Tensairity girder is a light weight inflatable fabric structural concept which can be used in road emergency transportation. It uses low pressure air to stabilize compression elements against buckling. With the purpose of obtaining the comprehensive target of minimum deflection and weight under ultimate load, the cross-section and the inner pressure of tensairity girder was optimized in this paper. The Variable Complexity Modeling (VCM) method was used in this paper combining the Kriging approximate method with the Finite Element Analysis (FEA) method, which was implemented by ABAQUS. In the Kriging method, the sample points of the surrogate model were outlined by Design of Experiment (DOE) technique based on Optimal Latin Hypercube. The optimization framework was constructed in iSIGHT with a global optimization method, Multi-Island Genetic Algorithm (MIGA), followed by a local optimization method, Sequential Quadratic Program (SQP). The result of the optimization gives a prominent conceptual design of the tensairity girder, which approves the solution architecture of VCM is feasible and efficient. Furthermore, a useful trend of sensitivity between optimization variables and responses was performed to guide future design. It was proved that the inner pressure is the key parameter to balance the maximum Von Mises stress and deflection on tensairity girder, and the parameters of cross section impact the mass of tensairity girder obviously.

• The KSFM Journal of Fluid Machinery
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• v.7 no.4 s.25
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• pp.7-15
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• 2004

The design point of the cross-flow fan is generally based on the region within low static pressure and high flow rate. It relatively makes high dynamic pressure at low speed because a working fluid passes through an impeller blade twice. However, it has low static pressure efficiency between $30\%$ and $40\%$ because of relative high impact loss. The purpose of this study is to research the reciprocal relation among each parameter. Experiments and numerical analyses are conducted on effects of a stabilizer and a rearguider on performance analysis of a cross-flow fan. Two-dimensional, unsteady governing equations are solved using FVM, PISO algorithm, sliding grid system and standard $k-{\epsilon}$ turbulence model. Experiments are also carried out to estimate the performance of the modeled cross-flow fan. It is clarified that the rearguider of Archimedes type has excellent results for the most part.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.04a
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• pp.309-312
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• 2007

The cryogenic fluid is the propellant for the liquid rocket engine. The design of space launcher vehicle is guided by minimum size and weight criteria, so the turbo pump solicits high impeller speed. Such high speed results in a zone of pressure drop below vapor pressure causing caivtation around inducer blades. The cryogenic fluid has different characters from isothermal fluid like water. The cryogenic fluid has very sensible thermodynamic properties and the phase change undergoes evaporative cooling. So, the developed code has to be modified cavitation modeling and it is added the energy equation for temperature sensitivity.

• The KSFM Journal of Fluid Machinery
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• v.16 no.6
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• pp.32-39
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• 2013

In the present study, three-dimensional aerodynamic optimization of high pressure turbine nozzle for turbofan engine was performed. For this, Kriging surrogate model was built and refined iteratively by supplying additional experimental points until the surrogate model and CFX result has effective difference on objective function. When the surrogate model satisfied this reliability condition and developed enough, optimum point was investigated. Commercial program PIAnO was used for optimization process and evolutionary algorithm was used for searching optimum point. As a result, difference between estimated value from Kriging surrogate model and CFD result converges within 0.01% and the optimized nozzle shape has 0.83% improved aerodynamic efficiency.

• Advances in aircraft and spacecraft science
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• v.11 no.2
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• pp.195-213
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• 2024

This article deals with the changes in flow air properties across an oblique shock wave for a real gas. The flow through is investigated to find a general form for oblique shock waves. The main objective of this work will result in the development of a new numerical algorithm to determine the effect of the stagnation pressure on supersonic flow for thermally and calorically imperfect gases with a molecular dissociation threshold, thus giving a better affinity to the physical behavior of the waves. So, the effects of molecular size and intermolecular attraction forces are used to correct a state equation, emphasizing the determination of the impact of upstream stagnation parameters on oblique shock waves. As results, the specific heat pressure does not remain constant and varies with the temperature and density. At Mach numbers greater than 2.0, the temperature rise considerably, and the density rise is well above, that predicted assuming ideal gas behavior. It is shown that caloric imperfections in air have an appreciable effect on the parameters developed in the processes is considered. Computation of errors between the present model based on real gas theory and a perfect gas model shows that the influence of the thermal and caloric imperfections associated with a real gas is important and can rise up to 16%.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2002.04a
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• pp.35-40
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• 2002

A numerical analysis based on two-dimensional and three-dimensional incompressible Navier-Stokes equations has been carried out for double-circular-arc compressor cascades and the results are compared with available experimental data at various incidence angles. The 2-D and 3-D computational codes based on SIMPLE algorithm adopt pressure weighted interpolation method for non-staggered grid and hybrid scheme for the convertive terms. Turbulence modeling is very important for prediction of cascade flows, which are extremely complex with separation and reattachment by adverse pressure gradient. In this paper k-$\varepsilon$ turbulence model with wall function is used to increase efficiency of computation times.