• Journal of Advanced Marine Engineering and Technology
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• v.30 no.2
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• pp.211-217
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• 2006

This study is focused on the analysis of the characteristics of marine HVAC duct. These results will be applied to develope a robot which is for maintaining a cabin comfort, convenience and healthy through HVAC duct. The followings are the results of this study. (1) The evaluated items which proposed by at the view point of robot's function can be adapted to other vessels for the same purpose, (2) For the case of round type duct. the maximized conditions which robot has to have are straight length of 40.152mm, inclination of $45^{\circ}$. horizontal bending of $90^{\circ}$. increasing diameter of 1.28 times, and 0.625 times decreasing diameter in branch. (3) For the case of rectangular type duct. the maximized conditions are straight length of 15.987mm. aspect ratio of 4.17:1, inclination of $18.92^{\circ}$. horizontal bending of $90^{\circ}$, and 0.65 times decreasing diameter in branch.

• International Journal of Fluid Machinery and Systems
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• v.6 no.2
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• pp.56-74
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• 2013

Stall stagnations in the system of axial-flow compressors and ducts occur in transition from deep surge conditions to decayed or converged stall conditions. The present study is concerned with the boundaries between the deep surges and the stagnation stalls on the basis of analytical results by a code on surge transients analysis and simulation. The fundamental acoustical-geometrical stagnation boundaries were made clear from examinations of the results on a variety of duct configurations coupled with a nine-stage compressor and a single stage fan. The boundary was found to be formed by three parts, i.e., B- and A-boundaries, and an intermediate zone. The B-boundary occurs for the suction-duct having a length of about a quarter of the wave-length of the first resonance in the case of very short and fat plenum-type delivery duct. On the other hand, the A-boundary occurs for the long and narrow duct-type delivery flow-path having a length about a fifth of the wavelength and relatively small sectional area in the case of short and narrow suction ducts. In addition to this, the reduced surge-cycle frequencies with respect to the duct lengths are observed to have respective limiting values at the stagnation boundaries. The reduced frequency for the B-boundary is related with a limiting value of the Greitzer's B parameter. The tendency and the characteristic features of the related flow behaviors in the neighborhood of the boundaries were also made clearer.

• Journal of Advanced Marine Engineering and Technology
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• v.22 no.6
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• pp.862-870
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• 1998

In this paper an experimental investigation of characteristics of developing transitional unsteady flows in a square-sectional 180。 curved duct are presented. The experimental study using air is carried out to measure axial velocity profiles secondary flow velocity profiles and entrance length by using Laser Do ppler Velocimeter(LDV) system. The flow development is found to depend upon Dean number dimensionless angular frequency velocity amplitude ration and cur-vature ratio. Of special interest is the secondary flow generated by centrifugal effects in the plane of the cross-section of the duct. The secondary flows are strong and complicate at entrance region. The entrance length of transitional pulsating flow is obtained to 120。 of bended angle of duct in this experimental conditions.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.2
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• pp.186-191
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• 2006

In this study, five experiments were carried out, with an orifice located downstream of a fan in case I where upstream duct length is 6 D, and that in the downstream is 4 D and different downstream distance to the fan in the rest, so as to determine the optimal location of the orifice and reduce the duct length of airflow measurement device. The resulting flow rate-pressure drop correlations were found to satisfy the limitation of SMACNA standard, which specified an error of $\pm7.5\%$ based on the real flow rate. Also, the best one of five. cases was achieved with the orifice located midway of the orifice duct four times its diameter long.

• Proceedings of the KSR Conference
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• 2011.05a
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• pp.70-77
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• 2011

When a train passes a conventional tunnel at high speed, an environmental noise issue arises by pressure variation and micro-pressure waves at the exit of the tunnel. It is known that this issue can be reduced by using dummy tunnel duct on the tunnel entrance. We studied the variances of micro-pressure waves at the exit of tunnel and pressure variation within the tunnel, by altering surface area and length of the dummy tunnel duct. For analyze this train-tunnel relation problem, axi-simmetric steady compressible flow solver was used. Changing the length of the dummy tunnel duct can adjust pressure variation, changing the surface area of the dummy tunnel duct can adjust volume and pressure variation of the micro-pressure wave. Thus, optimized surface area and length of the dummy tunnel duct can simultaneously reduce environmental noise pollution by micro-pressure wave and issues by the pressure variation.

• Journal of Biosystems Engineering
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• v.18 no.3
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• pp.275-287
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• 1993

The flow characteristics of the transitional oscillatory flows are investigated analytically and experimentally in the entrance region of a square duct. The systems of conservation equations are analytically solved by linearizing the non-linear convective terms for the developing transitional oscillatory flows in a square duct. The analytical solutions are obtained in the form of infinite series for the velocity profiles. The experimental study for the air flow in a square duct is carried out to measure the velocity profiles and waveforms by using a hot-wire anemometer with the data acquisition and processing systems. The theoretical and experimental results provide the major characteristics of the developing transitional oscillatory flows, such as velocity profiles, velocity waveforms, and entrance length. The velocity profiles in the decelerating phase are larger than those in the accelerating phase for the developing transitional oscillatory flows. The correlations of the entrance length of the transitional oscillatory flows in a square duct are found to be $Le/Dh=K{\cdot}Re_{os}/2({\omega}^+)^2$, where K is 1.23 of an experimental constant.

• Journal of the Korean Society of Propulsion Engineers
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• v.9 no.3
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• pp.1-9
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• 2005

An acoustic analysis of a fuel-rich gas generator for the drive of a turbopump in a liquid rocket engine has been performed and the length of a duct has been determined by comparing the resonant frequency of unstable acoustic modes to simulate an flight model gas generator, A practical short-length simulating duct has been determined by considering 1 or 2 wavelength of the unstable modes. Length adjustment of duct to turbopump can be a method to suppress a combustion instability problem by decoupling of acoustic mode and combustion characteristics. This method has been set up and validated with acoustic analysis and hot firing tests.

• Journal of the Society of Naval Architects of Korea
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• v.53 no.5
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• pp.343-352
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• 2016

In this study, a pre-swirl duct for the 180,000 DWT bulk carrier has been designed from a propulsion standpoint using CFD. The stern duct - designed by NMRI - was selected as the initial duct. The objective function is to minimize the value of delivered power in model scale. Design variables of the duct include duct angle, diameter, chord length, and vertical and horizontal displacements from the center. Design variables of the stators are blade number, arrangement angle, chord length, and pitch angle. A parametric design was carried out with the objective function obtained using CFD. Reynolds averaged Navier-Stokes equations have been solved; and the Reynolds stress model applied for the turbulent closure. A double body model is used for the treatment of free-surface. MRF and sliding mesh models have been applied to simulate the actuating propeller. A self-propulsion point has been obtained from the results of towing and self-propelled computations, i.e., form factor obtained from towing computation and towing forces obtained from self-propelled computations of two propeller rotating speeds. The reduction rate of the delivered power of the improved stern duct is 2.9%, whereas that of the initial stern duct is 1.3%. The pre-swirl duct with one inner stator in upper starboard and three outer stators in portside has been designed. The delivered power due to the designed pre-swirl duct is reduced by 5.8%.

• Journal of the Society of Naval Architects of Korea
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• v.56 no.4
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• pp.373-382
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• 2019

This paper shows numerical results for the estimation of the propulsor efficiency of Pre-Swirl Duct for 176k bulk carrier as well as its design method. Reynolds averaged Navier-Stokes equations have been solved and the k-epsilon model applied for the turbulent closure. The propeller rotating motion is determined using a sliding mesh technique. The design process is divided into each part of Pre-Swirl Duct, duct and Pre-Swirl Stator. The design of duct was performed first because it is located further upstream than Pre-Swirl Stator. The distribution of velocity through the duct was analyzed and applied for the design of Pre-Swirl Stator. The design variables of duct include duct angle, diameter, and chord length. Diameter, chord length, equivalent angle are considered when designing the Pre-Swirl Stator. Furthermore, a variable pitch angle stator is applied for the final model of Pre-Swirl Duct. The largest reduction rate of the delivered power in model scale is 7.6%. Streamlines, axial and tangential velocities under the condition that the Pre-Swirl Duct is installed were reviewed to verify its performance.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.6
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• pp.468-475
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• 2016

The purpose of this study is to investigate the acoustic problems of the conventional heat recovery ventilator and to suggest the methods of noise reduction from a heat recovery ventilator according to the installed location. The noise level, in this study, was measured and discussed as the parameters of size, wind volume and sound absorbing duct length for a heat recovery ventilator based on domestic and international related standards. It is found, as a result, that almost all of noise levels from the small and medium heat recovery ventilators without the sound absorbing duct in the anechoic chamber were higher than the noise standard value of 50 dB(A) regardless of the wind volume, and the noise levels went down when a sound absorbing duct was installed. In addition, the sound pressure level relative to frequency bands according to the length of sound absorbing duct was generally decreased, as the length of sound absorbing duct in the small and medium heat recovery ventilators was big, and the sound pressure level was generally increased, as the wind volume was great.