共查询到10条相似文献,搜索用时 140 毫秒
1.
Youngmin Bae Jae Young Jang Young J. Moon 《Journal of Mechanical Science and Technology》2008,22(7):1426-1435
This study numerically investigates the effects of fluid-structure interaction (FSI) on the trailing-edge noise, particularly
for the cases of wake instability and Karman vortex shedding. The trailing edge is modeled as a flat plate with an elastic
cantilever end and its flow-induced vibration is solved by an eigenmode analysis with the Galerkin method. The flow and sound
coupled in the FSI analysis are computed on the moving grid by a direct numerical simulation (DNS) procedure. The computed
result of wake instability shows that when the first-eigenmode natural frequency ω
n
of the cantilever is close to be resonant with the wake characteristic frequency ω
c
, the sound pressure level (SPL) is significantly reduced by 20 dB at ω
n
/ω
c
=0.95, or increased by 15 dB at ω
n
/ω
c
=1.05, for all angles. For the Karman vortex shedding, a similar frequency modulation occurs via FSI, if ω
n
is close to ω
c
. The flow and acoustic details are somewhat different for this case but a considerable noise reduction was also possible
for angles from −120° to +120°. 相似文献
2.
Hong-il Choi Pa-ul Mun Jae-soo Kim 《Journal of Mechanical Science and Technology》2009,23(6):1702-1709
Flight vehicles such as wheel wells and bomb bays have many cavities. The flow around a cavity is characterized as an unsteady
flow because of the formation and dissipation of vortices brought about by the interaction between the free stream shear layer
and the internal flow of the cavity. The resonance phenomena can damage the structures around the cavity and negatively affect
the aerodynamic performance and stability of the vehicle. In this study, a numerical analysis was performed for the cavity
flows using the unsteady compressible three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equation with Wilcox’s turbulence
model. The Message Passing Interface (MPI) parallelized code was used for the calculations by PC-cluster. The cavity has aspect
ratios (L/D) of 2.5 ∼ 7.5 with width ratios (W/D) of 2 ∼ 4. The Mach and Reynolds numbers are 0.4 ∼ 0.6 and 1.6×10
6
, respectively. The occurrence of oscillation is observed in the “shear layer and transient mode” with a feedback mechanism.
Based on the Sound Pressure Level (SPL) analysis of the pressure variation at the cavity trailing edge, the dominant frequencies
are analyzed and compared with the results of Rossiter’s formula. The dominant frequencies are very similar to the result
of Rossiter’s formula and other experimental data in the low aspect ratio cavity (L/D = ∼ 4.5). In the large aspect ratio cavity, however, there are other low dominant frequencies due to the leading edge shear
layer with the dominant frequencies of the feedback mechanism. The characteristics of the acoustic wave propagation are analyzed
using the Correlation of Pressure Distribution (CPD).
This paper was recommended for publication in revised form by Associate Editor Do Hyung Lee
Hong-il CHOI received the B.S and M.S degrees in Aerospace Engineering from Chosun University, Korea in 2005 and 2008, respectively. He
currently work at KOREA Electric Power Research Institute in Korea
Pa-ul MUN received the B.S in Aerospace Engineering from Chosun University, Korea in 2008. He is currently Candidate for the degree
of master of Aerospace Engineering at Chosun University in Korea.
Jae-soo KIM received the B.S in Aerospace Engineering from Seoul National University in Korea in 1981. He then received his M.S and Ph.D.
degree in Aerospace Engineering from KAIST in Korea in 1983 and 1987, respectively. He spent one year at Cornell university(USA)
as a Post Doc. He worked at Korea Aerospace Research Institute for eight years. Dr. Kim is currently a Professor at the Department
of Aerospace Engineering at Chosun University in Korea 相似文献
3.
Chel Hun Woo Jae Soo Kim Kyung Hwan Lee 《Journal of Mechanical Science and Technology》2006,20(8):1256-1265
The supersonic flows around tandem cavities were investigated by two-dimensional and three-dimensional numerical simulations
using the Reynolds-Averaged Navier-Stokes (RANS) equation with thek-ω turbulence model. The flow around a cavity is characterized as unsteady flow because of the formation and dissipation of
vortices due to the interaction between the freestream shear layer and cavity internal flow, the generation of shock and expansion
waves, and the acoustic effect transmitted from wake flow to upstream. The upwind TVD scheme based on the flux vector split
with van Leer’s limiter was used as the numerical method. Numerical calculations were performed by the parallel processing
with time discretizations carried out by the 4th-order Runge-Kutta method. The aspect ratios of cavities are 3 for the first
cavity and 1 for the second cavity. The ratio of cavity interval to depth is 1. The ratio of cavity width to depth is 1 in
the case of three dimensional flow. The Mach number and the Reynolds number were 1.5 and 4.5 × 105, respectively. The characteristics of the dominant frequency between twodimensional and three-dimensional flows were compared,
and the characteristics of the second cavity flow due to the first cavity flow was analyzed. Both two dimensional and three
dimensional flow oscillations were in the ‘shear layer mode’, which is based on the feedback mechanism of Rossiter’s formula.
However, three dimensional flow was much less turbulent than two dimensional flow, depending on whether it could inflow and
outflow laterally. The dominant frequencies of the two dimensional flow and three dimensional flows coincided with Rossiter’s
2nd mode frequency. The another dominant frequency of the three dimensional flow corresponded to Rossiter’s 1st mode frequency. 相似文献
4.
Jin Sung Lee Tae Gyu Kim Tae Sang Park Choong Sik Kim Chan Hoon Park 《Journal of Mechanical Science and Technology》2002,16(7):966-974
An analytic approach has been employed to study condensate film thickness distribution inside cave-shaped cavity of a flat
plate heat pipe. The results indicate that the condensate film thickness largely depends on mass flow rate and local velocity
of condensate. The increasing rate of condensate film for circular region reveals about 50% higher value than that of vertical
region. The physical properties of working fluid affect significantly the condensate film thickness, such as the condensate
film thickness for the case of FC-40 are 5 times larger than that of water. In comparison with condensation on a vertical
wall, the average heat transfer coefficient in the cave-shaped cavity presented 10-15% lower values due to the fact that the
average film thickness formed inside the cave-shaped cavity was larger than that of the vertical wall with an equivalent flow
length. A correlation formula which is based on the condensate film analysis for the cave-shaped cavity to predict average
heat transfer coefficient is presented. Also, the critical minimum fill charge ratio of working fluid based on condensate
film analysis has been predicted, and the minimum fill charge ratios for FC-40 and water are about Ψcrit= 3-7%, Ψcrit=0.5-1.3%, respectively, in the range of heat fluxq” = 5-90kW/2 相似文献
5.
Soon-Bum Kwon Sung-Jin Lee Seung-Young Shin Sung-Ha Kim 《Journal of Mechanical Science and Technology》2009,23(6):1736-1742
As recognized previously, a minimum-length nozzle has the smallest possible throat-to-exit length that is still capable of
maintaining uniform supersonic flow at the nozzle exit. In the present study, for the flow of moist air through a nearly minimum-length
nozzle designed by the method of characteristics, the effects of nonequilibrium condensation on the uniformity of flow properties,
the momentum efflux, and the flow distortion at the nozzle exit plane are discussed by experiment and numerical analysis of
a third-order Total Variation Diminishing (TVD) finite difference scheme. The onset and zone of nonequilibrium condensation
in a minimum-length nozzle are quite different from those of a general convergent-divergent supersonic nozzle. We know that
the uniformity of flow properties at the nozzle exit with regard to the flow with nonequilibrium condensation in a minimum-length
nozzle cannot be guaranteed. On the other hand, owing to the positions of the onset of condensation at the incident region
of expansion waves from the sharp corner just downstream of the nozzle throat, the deceleration gradient and magnitude of
heat released from the process of nonequilibrium condensation to the surrounding of ϕ0=60% are greater than those of ϕ0=70% in the case of T0=290K. Furthermore, it has been determined that the decrease in efflux of momentum from the nozzle exit for the stagnation
relative humidity of ϕ0=70%(T0=290K), which corresponds to the case with nonequilibrium condensation shock, is 6.8% smaller than that of isentropic expansion.
This paper was recommended for publication in revised form by Associate Editor Do Hyung Lee
Soon-Bum Kwon received his B.S. and M.S. degrees in Mechanical Engineering from Kyungpook National University in 1974 and 1980, respectively,
and his Ph.D. degree from Kyushu University in 1987. He is a Professor at the School of Mechanical Engineering at Kyungpook
National University. His research interests are compressible gas dynamics and nonequilibrium condensation. 相似文献
6.
Kwang Ho Lee Arun Shukla Venkitanarayanan Parameswaran Vijaya Chalivendra Jae Sug Hawong 《Journal of Mechanical Science and Technology》2002,16(2):165-174
In the present study, interfacial cracks between an isotropic and orthotropic material, subjected to static far field tensile
loading are analyzed using the technique of photoelasticity. The fracture parameters are extracted from the full-field isochromatic
data and the same are compared with that obtained using boundary collocation method. Dynamic photoelasticity combined with
high-speed digital photography is employed for capturing the isochromatics in the case of propagating interfacial cracks.
The normalized stress intensity factors for static cracks are greater when α=90° (fibers perpendicular to the interface) than
when α=0° (fibers parallel to the interface), and those when α=90° are similar to ones of isotropic material. The dynamic
stress intensity factors for interfacial propagating cracks are greater when α=0° than α=90°. For the velocity ranges (0.1<c/c
s1
<0.7) observed in this study, the complex dynamic stress intensity factor |K
D
|, I increases with crack speedc, however, the rate of increase of |K
D
| with crack speed is not as drastic as that reported for homogeneous materials. 相似文献
7.
Woo-Gon Kim Sung-Ho Kim Woo-Seog Ryu 《Journal of Mechanical Science and Technology》2001,15(11):1463-1471
The Kachanov and Rabotnov (K-R) creep damage model was interpreted and applied to type 316LN and HT-9 stainless steels. Seven creep constants of the model,A, B. k, m, λ, γ, andq were determined for type 316LN stainless steel. In order to quantify a damage parameter, the cavity was interruptedly traced during creep for measuring cavity area to be reflected into the damage equation. For type 316LN stainless steel, λ=ε R /ε* and λ f =ε/ε R were 3.1 and increased with creep strain. The creep curve with λ=3.1 depicted well the experimental data to the full lifetime and its damage curve showed a good agreement whenr=24. However for the HT-9 stainless steel, the values of A and A/ were different as λ=6.2 and λ f =8.5, and their K-R creep curves did not agree with the experimental data. This mismatch in the HT-9 steel was due to the ductile fracture by softening of materials rather than the brittle fracture by cavity growth. The differences of the values in the above steels were attributed to creep ductilities at the secondary and the tertiary creep stages. 相似文献
8.
The effect of acoustic noise on combustion is investigated from the perspective of NOx emissions. A robust, plug-in probe that exploits the natural emission signal from the combustion gases, and which can have
practical relevance, is used. Acoustically pulsed flames are stabilized on aburner, and NO2 chemiluminescence is measured with an intensified detector at various frequencies. The results indicate the NO2 emission increases in noisy flames at certain frequencies more significantly than others. Noise at higher frequencies in
the range 0.8≈1 kHz effects the nitrogen chemistry in stoichiometric flames (ϕ=1), but not that in lean flames (ϕ-0.7 and
0.8). 相似文献
9.
Jiraporn Yojina Waipot Ngamsaad Narin Nuttavut Darapond Triampo Yongwimon Lenbury Paisan Kanthang Somchai Sriyab Wannapong Triampo 《Journal of Mechanical Science and Technology》2010,24(10):2025-2034
In this work, mesoscopic modeling via a computational lattice Boltzmann method (LBM) is used to investigate the flow pattern
phenomena and the physical properties of the flow field around one and two square obstacles inside a two-dimensional channel
with a fixed blockage ratio, β=1/4, centered inside a 2D channel, for a range of Reynolds numbers (Re) from 1 to 300. The simulation results show that flow
patterns can initially exhibit laminar flow at low Re and then make a transition to periodic, unsteady, and, finally, turbulent
flow as the Re get higher. Streamlines and velocity profiles and a vortex shedding pattern are observed. The Strouhal numbers
are calculated to characterize the shedding frequency and flow dynamics. The effect of the layouts or configurations of the
obstacles are also investigated, and the possible connection between the mixing process and the appropriate design of a chemical
mixing system is discussed. 相似文献
10.
Dong-Ho Min Kyung-Beom Yoon Hee-Chul Chang Tae-Kuk Kim 《Journal of Mechanical Science and Technology》2008,22(7):1436-1443
The purpose of this research is to study numerically the turbulent gas-particle two-phase flow characteristics using the Eulerian-Eulerian
method. A computer code is developed for the numerical study by using the k-ɛ-k
p
two-phase turbulent model. The developed code is applied for particle-laden flows in which the particle volume fraction is
between 10−5 and 10−2 for the Stokes numbers smaller than unity. The gas and particle velocities and the particle volume fraction obtained by using
this code are in good agreement with those obtained by a commercial code for the gas-particle jet flows within a rectangular
enclosure. The gas-particle jet injected into a vertical rectangular 3D enclosure is numerically modeled to study the effect
of the Stokes number, the particle volume fraction and the particle Reynolds numbers. The numerical results show that the
Stokes number and the particle volume fraction are important parameters in turbulent gas-particle flows. A small Stokes number
(St ≤ 0.07) implies that the particles are nearly at the velocity equilibrium with the gas phase, while a large Stokes number
(St ≥ 0.07) implies that the slip velocity between the gas and particle phase increases and the particle velocity is less affected
by the gas phase. A large particle volume fraction (α
p
≥ 0.0001) implies that the effect of the particles on the gas phase momentum increases, while a small particle volume fraction
(α
p
≤ 0.0001) implies that the particles would have no or small effect on the gas flow field. For fixed Stokes number and particle
volume fraction, an increase of the particle Reynolds number results in a decrease of the slip velocity between the gas and
particle velocities. 相似文献