• International Journal of Railway
• /
• v.4 no.3
• /
• pp.74-79
• /
• 2011

Recent years have witnessed speed up of moving vehicles such as high-speed of trains. Increase in speed entails concomitant increase in turbulent air flow which contributes toward increased aerodynamic noise. The proposed method for aerodynamic noise reduction is based on a biomimetic design of owl feather. The five morphological parameters of the owl feather are extracted from close observation, and simulation cases are constructed by applying design of experiments methodology. Swirling strength for each case is obtained through steady-state CFD analysis, and key morphological parameters that affect the turbulence are identified. Large eddy simulations (LES) are then performed on selected cases to predict the air turbulence. Different cases show varying vortex distributions which are expected to lead to varying aerodynamic noise levels.

• Phonetics and Speech Sciences
• /
• v.6 no.3
• /
• pp.57-62
• /
• 2014

The present study was performed to investigate and discuss the aerodynamic characteristics of whispered and normal speech during reading paragraph tasks. 39 normal females(18-23 yrs.) read 'Autumn' paragraph with whispered and normal phonation. Their readings were recorded and analyzed by 'Running Speech' in Phonatory Aerodynamic System(PAS) instrument. As results, during whispered speech, the total duration was longer and the numbers of inspiration were more frequently shown than normal speech. The Peak expiratory and inspiratory rate were higher in normal speech, but the expiratory and inspiratory volume were higher in whispered speech. By correlation analysis, both whispered and normal speech showed significantly high correlation between total duration and expiratory/inspiratory airflow duration; numbers of inspiration and inspiratory airflow duration; expiratory and inspiratory volume. These results show that whispered speech needs more respiratory effort but shows poorer aerodynamic efficacy during phonation than normal speech.

• 연구논문집
• /
• s.25
• /
• pp.13-22
• /
• 1995

At the running speed higher than 250 km/h, several aerodynamic problems such as the increase of aerodynamic resistance, aerodynamic noise, pressure fluctuation at the tunnel entry, impulsive wave at the tunnel exit bring about the power consumption, deterioration of riding quality, and severe environmental noise. To solve these aerodynamic problems, the flow phenomena around the high speed train have to be analyzed in detail. In this study, the flow around the train is modelled as the 2-dimensional viscous compressible flow and the flow field is calculated numerically for the three different types of geometry and running speed. The aerodynamic drag coefficient and the pressure coefficient are evaluated each case.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.25 no.4
• /
• pp.507-513
• /
• 2001

Time averaged pressure distributions in a high-speed centrifugal compressor channel diffuser at design and off-design flow rates are investigated. Pressure distributions from the impeller exit to the channel diffuser exit are measured for various flow rates from choke to near surge condition, and the effects of operating condition are discussed. The strong non-uniformity in the pressure distribution is obtained over the vaneless space and semi-vaneless space caused by the impeller-diffuser interaction. As the flow rate increases, flow separation near the throat, due to large incidence angle at the vane leading edge, increases aerodynamic blockage and reduces the aerodynamic flow area downstream. Thus the minimum pressure location occurs downstream of the geometric throat, and it is named as the aerodynamic throat. And at choke condition, normal shock occurs downstream of this aerodynamic throat. The variation in the location of the aerodynamic throat is discussed.

• Proceedings of the KSME Conference
• /
• 2000.04b
• /
• pp.548-554
• /
• 2000

The aim of this paper is to understand the time averaged pressure distributions in a high-speed centrifugal compressor channel diffuser at design and off-design flow rates. Pressure distributions from the impeller exit to the channel diffuser exit are measured and discussed far various flow rates from choke to near surge condition, and the effect of operating condition is discussed. The strong non-uniformity in the pressure distribution is obtained over the vaneless space and semi-vaneless space caused by the impeller-diffuser interaction. As the flow rate increases, flow separation near the throat, due to large incidence angle at the vane leading edge, increases aerodynamic blockage and reduces the aerodynamic flow area downstream. Thus the minimum pressure location occurs downstream of the geometric throat, and it is named as the aerodynamic throat. And at choke condition, normal shock occurs downstream of this aerodynamic throat. The variation in the location of the aerodynamic throat is discussed.

• Proceedings of the KSME Conference
• /
• 2003.11a
• /
• pp.556-561
• /
• 2003

Flight bodies are subject to highly unstable and severe flow conditions during taking-off and landing periods. In this situation, the flight bodies essentially experience accelerating or decelerating flows, and the aerodynamic characteristics can be completely different from those of steady flows. In the present study, unsteady aerodynamic characteristics of an aerofoil accelerating at subsonic speeds are investigated using a computational method. Two-dimensional, unsteady, compressible Navier-Stokes simulations are conducted with a one-equation turbulence model, Spalart-Allmaras, and a fully implicit finite volume scheme. An acceleration factor is defined to specify the unsteady aerodynamics of the aerofoil. The results show that the acceleration of the subsonic aerofoil generally leads to a variation in aerodynamic characteristics and it is more significant at angles of attack.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2002.05a
• /
• pp.677-683
• /
• 2002

The analytical and experimental studies on aerodynamic flutter instability of rotating disks in information storage devices are investigated. The theoretical analysis uses a fluid-structure model where the aerodynamic force on the rotating disk is represented in terms of lift and damping forces. Based on the analytical approach, it is shown that the backward natural frequency of the disk is equal to that of the case without aerodynamic effect at the flutter onset speed. In post-flutter regions, the natural frequencies are larger than those in vacuum conditions without aerodynamic effect. The analytical predictions on the natural frequencies of rotating disks with/without aerodynamic effect are experimentally verified using a vacuum chamber and ASMO optical disks.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.30 no.9 s.252
• /
• pp.913-920
• /
• 2006

Three-dimensional flow and aerodynamic loss in the tip-leakage flow region of a high-turning first-stage turbine rotor blade with a squealer tip have been measured with a straight miniature five-hole probe for the tip gap-to-chord ratio, h/c, of 2.0%. This squealer tip has a indent-to-chord ratio, $h/{st}/c$, of 5.5%. The results are compared with those for a plane tip $(h_{st}/c=0.0%)$. The squealer tip tends to reduce the mass flow through the tip gap and to suppress the development of the tip-leakage vortex. Therefore, it delivers lower aerodynamic loss in the near-tip region than the plane tip does. At the mid-span, however, the aerodynamic loss has nearly the same value for the two different tips.

• Journal of the Korean Society of Laryngology, Phoniatrics and Logopedics
• /
• v.9 no.1
• /
• pp.5-10
• /
• 1998

Voice rehabilitation is very important concerning in laryngectomees. Esophageal speech is a common and widely used method of voice restoration. But, until now there is no reliable data which shows the aerodynamic characteristics of esophageal speech. In order to evaluate the vocal quality of normal laryngeal and esophageal speech, several aerodynamic parameters were measured in 13 adults with normal laryngeal voice and 2 excellent esophageal speakers using Aerophone II voice function analyzer. The examined parameters were maximal flow rate, mean airflow rate, subglottic pressure, vocal efficiency, glottic resistance, maximal phonation time and mean sound pressure level. In vocal efficiency, there is no difference between two groups, but in other parameters, marked differences were showed in esophageal speakers, especially mean resistance. Results indicates that esophageal speakers make the efficient voices with poor aerodynamic condition, comparing with normal laryngeal speakers.

• Journal of the Korean Society for Aviation and Aeronautics
• /
• v.8 no.1
• /
• pp.83-95
• /
• 2000

Lift, drag, pitching moment, what we call longitudinal aerodynamic coefficient, effects airplanes directly, so the method to find the accurate result quickly is an important factor from the beginning of the aircraft design. There are different ways to find aerodynamic coefficient such as empirical methods, numerical analysis methods, wind tunnel tests, and finally through an actual flight tests, but choosing the best methods depends on the due date or the cost. The accuracy varies on each design level, but all this methods have relationship to complement and balance each other, so by combining proper methods, the best result can be obtained. At this paper, empirical methods and numerical analysis method were experimented, compared, and reviewed to find the availability of each method and by combining two methods accurate result was obtained. So, we applied this methods to predict the aerodynamic coefficient on cruise configuration aircraft, and was able to obtain more accurate result on the low speed longitudinal aerodynamic coefficient. Also by watching there result, we are able to predict the errors before the actual wind tunnel test.