• Nuclear Engineering and Technology
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• v.55 no.4
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• pp.1310-1323
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• 2023

A reactor coolant pump (RCP) is essential for transporting coolant in the primary loop of pressurized water reactors. In the advanced passive reactor, the absence of a long pipeline between the steam generator and RCP serves as a transition section, resulting in a non-uniform flow field at the pump inlet. Therefore, the characteristics of the pump should be investigated under non-uniform flow to determine its influence on the pump. In this study, the pressure pulsation characteristics were examined in the time and frequency domains, and the sources of low-frequency and high-amplitude signals were analyzed using wavelet coherence analysis and numerical simulation. From computational fluid dynamics (CFD) results, non-uniform inflow has a great effect on the flow structures in the pump's inlet. The pressure pulsation in the pump at the rated flow increased by 78-128.7% under the non-uniform inflow condition in comparison with that observed under the uniform inflow condition. Furthermore, a low-frequency signal with a high amplitude was observed, whose energy increased significantly under non-uniform flow. The wavelet coherence and CFD analysis verified that the source of this signal was the low-frequency pulsating vortex under the steam generator.

• International Journal of Fluid Machinery and Systems
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• v.10 no.2
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• pp.138-145
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• 2017

The problem of non-uniform inflow exists in many practical engineering applications, such as the elbow suction pipe of waterjet pump and, the channel head of steam generator which is directly connect with reactor coolant pump. Generally, pumps are identical designs and are selected based on performance under uniform inflow with the straight pipe, but actually non-uniform suction flow is induced by upstream equipment. In this paper, CFD approach was employed to analyze unsteady hydrodynamic characteristics of reactor coolant pumps with different inflows. The Reynolds-averaged Naiver-Stokes equations with the $k-{\varepsilon}$ turbulence model were solved by the computational fluid dynamics software CFX to conduct the steady and unsteady numerical simulation. The numerical results of the straight pipe and channel head were validated with experimental data for the heads at different flow coefficients. In the nominal flow rate, the head of the pump with the channel head decreases by 1.19% when compared to the straight pipe. The complicated structure of channel head induces the inlet flow non-uniform. The non-uniformity of the inflow induces the difference of vorticity distribution at the outlet of the pump. The variation law of blade to blade velocity at different flow rate and the difference of blade to blade velocity with different inflow are researched. The effects of non-uniform inflow on radial forces are absolutely different from the uniform inflow. For the radial forces at the frequency $f_R$, the corresponding amplitude of channel head are higher than the straight pipe at $1.0{\Phi}_d$ and $1.2{\Phi}_d$ flow rates, and the corresponding amplitude of channel head are lower than the straight pipe at $0.8{\Phi}_d$ flow rates.

• International Journal of Aeronautical and Space Sciences
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• v.12 no.2
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• pp.156-162
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• 2011

The preliminary design stage of helicopters consists of various operations and in each operation design several detailed analysis tasks are needed. The analysis tasks include performance and the required power estimation. In helicopter design, those are usually carried out by adopting the momentum theory. In this paper, an explicit form of computational analysis based on the blade element theory and uniform/non-uniform inflow model is developed. The other motivation of the present development is to obtain trim and required power estimation for various helicopter configurations. Sectional and hub loads, power, trim, and flapping equations are derived by using a symbolic tool. Iterative computations are carried out till convergence is achieved in the blade response, inflow, and trim. The predictions regarding the trim and power estimation turn out to be correlated well with the experimental results. The effect of inflow is further investigated. It is found that the present prediction for the lateral cyclic pitch angle is improved with the non-uniform inflow model as compared to that by the uniform inflow model. The presently improved trim and power estimation will be useful for future helicopter sizing and performance analysis.

• Wind and Structures
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• v.30 no.6
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• pp.649-662
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• 2020

The existence of a dam has potential effects on the surrounding wind environment especially when it is located in mountainous areas. In this situation, the long-span bridge over the reservoir can easily be exposed to non-uniform incoming flows, affecting its wind-resistance performance. This paper presents a study on the aerostatic stability of such a bridge. Wind tunnel tests were first carried out to investigate the wind environment above a mountainous reservoir. The results show that the angle of attack and the wind speed along the bridge axis show obvious non-uniform characteristics, which is related to the inflow direction. When winds come from the south where the river is winding, the angle of attack varies along the span direction significantly. The finite element model for the bridge was established using ANSYS software, and effects of non-uniform wind loads on the aerostatic stability were computed. Non-uniform angle of attack and wind speed are unfavorable to the aerostatic stability of the bridge, especially the former. When the combined action of non-uniform angle of attack and wind speed is considered, the critical wind speed of aerostatic instability is further reduced. Moreover, the aerostatic stability of the bridge is closely related to the dam height.

• The KSFM Journal of Fluid Machinery
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• v.11 no.4
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• pp.38-44
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• 2008

This paper describes the performance and internal flow characteristics of two-stage high pressure ring blower. Chamber-type test rig is designed and manufactured for the performance test of the ring blower. Detailed flow characteristics inside the impeller and casing are analyzed by three-dimensional numerical simulation. Throughout numerical simulation, non-uniform inflow to the impeller inlet and reverse flow are observed near the inlet duct of the blower. This non-uniform inflow makes various recirculation flow inside the casing with the complicated shape of casing. Low velocity region is locally formed near the both sides of impeller outlet due to the non-uniform inflow to the impeller, thus deteriorates the performance of a ring blower.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.17-22
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• 2002

Non-uniform and unsteady inflow into a Horizontal Axis Wind Turbine (HAWT) brings about an asymmetric flow field on the rotor plane and an unsteady aerodynamic load on the blades. In the present paper effects of yawed inflow and wind shear are analyzed by an inviscid aerodynamic model based on the asymptotic acceleration potential method. In the analysis the rotor blades are represented by spanwise and chordwise pressure distribution composed of analytical first-order asymptotic solutions for the Laplace equation. As the actual wind field experienced by a HAWT is turbulent, the effects of the turbulence are also examined using the Veers' model.

• International Journal of High-Rise Buildings
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• v.8 no.4
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• pp.255-264
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• 2019

This paper describes large eddy simulation of wind pressures on a square cylinder in a uniform flow and a high-rise building immersed in an atmospheric turbulent boundary layer. For the atmospheric boundary layer case, the inflow turbulence is generated by a numerical wind tunnel. In the numerical simulation, particular attention is devoted to the performance of an auto hexahedral non-structural mesh. Both simulations are performed for three grid systems: an auto hexahedral non-structured grid, a structured Cartesian grid and a non-structured triangular prism grid, and for three grid numbers. The present study shows that the auto hexahedral unstructured mesh achieves the best simulation results for wind pressures on the square cylinder and the high-rise building. When the grid number is sufficiently large, the differences among the results obtained from the three investigated grid systems are not significant. However, the advantage of the auto hexahedral unstructured mesh becomes clear when the grid number decreases, because it enables a balanced distribution of orthogonal grids. The results described in this paper demonstrate that the auto hexahedral non-structured mesh has good potential applicability to simulation of urban flows.

• International Journal of Aeronautical and Space Sciences
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• v.16 no.4
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• pp.614-623
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• 2015

When the speed of a coaxial rotor helicopter in forward flight increases, the wake skew angle of the rotor increases and consequently the position of the vena contracta of the upper rotor with respect to the lower rotor changes. Considering ambient air and the effect of the upper rotor, this study proposes a nonuniform inflow model for the lower rotor of a coaxial rotor helicopter in forward flight. The total required power of the coaxial rotor system was compared against Dingeldein's experimental data, and the results of the proposed model were well matched. A plant model was also developed from first principles for flight simulation, unknown parameter estimation and control analysis. The coaxial rotor helicopter used for this study was manufactured for surveillance and reconnaissance and does not have any stabilizer bar. Therefore, a feedback controller was included during flight test and parameter estimation to overcome unstable situations. Predicted responses of parameter estimation and validation show good agreement with experimental data. Therefore, the methodology described in this paper can be used to develop numerical plant model, study non-uniform inflow model, conduct performance analysis and parameter estimation of coaxial rotor as well as other rotorcrafts in forward flight.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.196-201
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• 2003

Axial fans are widely used for automotive engine cooling device due to their ability to produce high flow rate to keep engine cool. At the same time, the noise generated by these fans causes one of the most serious problems. Especially, engine cooling fan noise in idle condition of a car is noticeable. Therefore, the high efficient and low-noise fan is seriously needed. When a new fan system is designed, system resistance and non-uniform inflow are the key factors to get the high performance and low noise fan system. In this study, experimental study on the fan and system was carried out and brought a successful result of performance and noise from a designed fan. And through the modification of the fan system, the fan produced more flow rate and became less noisy.

• 유체기계공업학회:학술대회논문집
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• 2005.12a
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• pp.663-669
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• 2005

Performance characteristics of an axial flow fan having distorted inlet flow have been investigated using numerical analysis as well as experiment. Two kinds of hub-cap, round shape and right-angled front shape, are tested to investigate the effect of inlet flow distortion on the fan performance. In case of right-angled front shape, axisymmetric distorted inflow is induced by flow separation at the sharp edge of hub-cap, and the characteristics of the inflow depends on the distance between hub-cap and blade leading edge. Flow analysis of the blade passage is peformed by solving the three-dimensional Reynolds-averaged Navier-Stokes equations. numerical solutions are validated in comparison with experimental data measured by a five-hole probe downstream of the fan rotor. It is found from the numerical results that non-uniform axial inlet velocity profile near the hub results in the change of inlet flowangle. The changed inlet flow angle near the hub invokesa flow separation on the blade surfaces, thus deteriorating the fan efficiency. The effect of the distance between hub-cap and blade leading edge on the efficiency is also discussed.