共查询到20条相似文献,搜索用时 15 毫秒
1.
D. Estruch D. G. MacManus J. L. Stollery N. J. Lawson K. P. Garry 《Experiments in fluids》2010,49(3):683-699
The understanding of the behaviour of the flow around surface protuberances in hypersonic vehicles is developed and an engineering
approach to predict the location and magnitude of the highest heat transfer rates in their vicinity is presented. To this
end, an experimental investigation was performed in a hypersonic facility at freestream Mach numbers of 8.2 and 12.3 and Reynolds
numbers ranging from Re
∞/m = 3.35 × 106 to Re
∞/m = 9.35 × 106. The effects of protuberance geometry, boundary layer state, freestream Reynolds number and freestream Mach numbers were
assessed based on thin-film heat transfer measurements. Further understanding of the flowfield was obtained through oil-dot
visualizations and high-speed schlieren videos. The local interference interaction was shown to be strongly 3-D and to be
dominated by the incipient separation angle induced by the protuberance. In interactions in which the incoming boundary layer
remains unseparated upstream of the protuberance, the highest heating occurs adjacent to the device. In interactions in which
the incoming boundary layer is fully separated ahead of the protuberance, the highest heating generally occurs on the surface
just upstream of it except for low-deflection protuberances under low Reynolds freestream flow conditions in which case the
heat flux to the side is greater. 相似文献
2.
Large-eddy simulations (LES) of a planar, asymmetric diffuser flow have been performed. The diverging angle of the inclined
wall of the diffuser is chosen as 8.5°, a case for which recent experimental data are available. Reasonable agreement between
the LES and the experiments is obtained. The numerical method is further validated for diffuser flow with the diffuser wall
inclined at a diverging angle of 10°, which has served as a test case for a number of experimental as well as numerical studies
in the literature (LES, RANS). For the present results, the subgrid-scale stresses have been closed using the dynamic Smagorinsky
model. A resolution study has been performed, highlighting the disparity of the relevant temporal and spatial scales and thus
the sensitivity of the simulation results to the specific numerical grids used. The effect of different Reynolds numbers of
the inflowing, fully turbulent channel flow has been studied, in particular, Re
b
= 4,500, Re
b
= 9,000 and Re
b
= 20,000 with Re
b
being the Reynolds number based on the bulk velocity and channel half width. The results consistently show that by increasing
the Reynolds number a clear trend towards a larger separated region is evident; at least for the studied, comparably low Reynolds-number
regime. It is further shown that the small separated region occurring at the diffuser throat shows the opposite behaviour
as the main separation region, i.e. the flow is separating less with higher Re
b
. Moreover, the influence of the Reynolds number on the internal layer occurring at the non-inclined wall described in a recent
study has also been assessed. It can be concluded that this region close to the upper, straight wall, is more distinct for
larger Re
b
. Additionally, the influence of temporal correlations arising from the commonly used periodic turbulent channel flow as inflow
condition (similar to a precursor simulation) for the diffuser is assessed. 相似文献
3.
A. A. Vasil’ev V. N. Rychkov M. E. Topchiyan 《Journal of Applied Mechanics and Technical Physics》2007,48(3):361-367
The laminar-turbulent transition is experimentally studied in boundary-layer flows on cones with a rectangular axisymmetric
step in the base part of the cone and without the step. The experiments are performed in an A-1 two-step piston-driven gas-dynamic
facility with adiabatic compression of the working gas with Mach numbers at the nozzle exit M
∞ = 12–14 and pressures in the settling chamber P0 = 60–600 MPa. These values of parameters allow obtaining Reynolds numbers per meter near the cone surface equal to Re
1e = (53–200) · 106
m
−1. The transition occurs at Reynolds numbers Re
tr
= (2.3–5.7) · 106.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 3, pp. 76–83, May–June, 2007. 相似文献
4.
Results of numerical simulations of the evolution of disturbances in a hypersonic shock layer on a flat plate at high Mach
numbers (M∞ = 21) and moderate Reynolds numbers (Re
L
= 1.44 · 105) are analyzed by an adapted method of bispectral analysis. All basic types of nonlinear interactions are obtained. The calculated
results are compared with experimental data. 相似文献
5.
Results of a numerical and experimental study of characteristics of disturbances in a hypersonic shock layer on a flat plate
covered by a sound-absorbing coating and aligned at an angle of attack are presented. Experiments and computations are performed
for the free-stream Mach number M
∞
= 21 and Reynolds number Re
L
= 6 · 104. A possibility of suppressing pressure fluctuations in the shock layer at frequencies of 20–40 kHz with the use of tubular
and porous materials incorporated into the plate surface is demonstrated. Results of numerical simulations are found to be
in good agreement with experimental data. 相似文献
6.
A. A. Maslov A. N. Kudryavtsev S. G. Mironov T. V. Poplavskaya I. S. Tsyryulnikov 《Journal of Applied Mechanics and Technical Physics》2007,48(3):368-374
Direct numerical simulations of the evolution of disturbances in a viscous shock layer on a flat plate are performed for a
free-stream Mach number M
∞ = 21 and Reynolds number Re
L = 1.44 · 105. Unsteady Navier-Stokes equations are solved by a high-order shock-capturing scheme. Processes of receptivity and instability
development in a shock layer excited by external acoustic waves are considered. Direct numerical simulations are demonstrated
to agree well with results obtained by the locally parallel linear stability theory (with allowance for the shock-wave effect)
and with experimental measurements in a hypersonic wind tunnel. Mechanisms of conversion of external disturbances to instability
waves in a hypersonic shock layer are discussed.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 3, pp. 84–91, May–June, 2007. 相似文献
7.
I. Recktenwald N. Alkishriwi W. Schrder 《European Journal of Mechanics - B/Fluids》2009,28(5):677-688
The flow field of a channel rotating about the streamwise axis is analyzed experimentally and numerically. The current investigations were carried out at a bulk velocity based Reynolds number of Rem = 2850 and a friction velocity based Reynolds number of Reτ = 180, respectively. Particle-image velocimetry (PIV) measurements are compared with large-eddy simulation data to show earlier direct numerical simulation findings to generate too large a reverse flow region in the center region of the spanwise flow. The development of the mean spanwise velocity distribution and the influence of the rotation on the turbulent properties, i.e., the Reynolds stresses and the two-point correlations of the flow, are confirmed in both investigations. The rotation primarily influences those components of the Reynolds shear stresses, which contain the spanwise velocity component. The size of the correlation areas and thus the length scales of the flow generally grow in all three coordinate directions leading to longer structures. Furthermore, experimental results of the same channel flow at a significantly lower bulk Reynolds number of Rem, l = 665, i.e., a laminar flow in a non-rotating channel, are introduced. The experiments show the low Reynolds number flow to become turbulent under rotation and to develop the same characteristics as the high Reynolds number flow. 相似文献
8.
This study investigates the flow past a confined circular cylinder built into a narrow rectangular duct with a Reynolds number
range of 1,500 ≤ Re
d
≤ 6,150, by employing the particle image velocimetry technique. In order to better explain the 3-D flow behaviour in the
juncture regions of the lower and upper plates and the cylinder, respectively, as well as the dynamics of the horseshoe vortex
system, both time-averaged and instantaneous flow data are presented for regions upstream and downstream of the cylinder.
The size, intensity and interaction of the vortex systems vary substantially with the Reynolds number. Although the narrow
rectangular duct with a single built-in cylinder is a geometrically symmetrical arrrangement, instantaneous flow data have
revealed that the flow structures in both the lower and upper plate–cylinder junction regions are not symmetrical with respect
to the centreline of the flow passage. The vortical flow structures obtained in side-view planes become dominant sometimes
in the lower juncture region and sometimes in the upper juncture region in unsteady mode. 相似文献
9.
A. N. Kudryavtsev S. G. Mironov T. V. Poplavskaya I. S. Tsyryul’nikov 《Journal of Applied Mechanics and Technical Physics》2006,47(5):617-627
The evolution of disturbances in a hypersonic viscous shock layer on a flat plate excited by slow-mode acoustic waves is considered
numerically and experimentally. The parameters measured in the experiments performed with a free-stream Mach number M
∞ = 21 and Reynolds number Re
L = 1.44 · 105 are the transverse profiles of the mean density and Mach number, the spectra of density fluctuations, and growth rates of
natural disturbances. Direct numerical simulation of propagation of disturbances is performed by solving the Navier-Stokes
equations with a high-order shock-capturing scheme. The numerical and experimental data characterizing the mean flow field,
intensity of density fluctuations, and their growth rates are found to be in good agreement. Possible mechanisms of disturbance
generation and evolution in the shock layer at hypersonic velocities are discussed.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 5, pp. 3–15, September–October, 2006. 相似文献
10.
M. H. A. van Dongen A. van Loon R. J. Vrancken J. P. C. Bernards J. F. Dijksman 《Experiments in fluids》2014,55(5):1-9
In the present study, the characteristics of supersonic rectangular microjets are investigated experimentally using molecular tagging velocimetry. The jets are discharged from a convergent–divergent rectangular nozzle whose exit height is 500 μm. The jet Mach number is set to 2.0 for all tested jets, and the Reynolds number Re is altered from 154 to 5,560 by changing the stagnation pressure. The experimental results reveal that jet velocity decays principally due to abrupt jet spreading caused by jet instability for relatively high Reynolds numbers (Re > ~450). The results also reveal that the jet rapidly decelerates to a subsonic speed near the nozzle exit for a low Reynolds number (Re = 154), although the jet does not spread abruptly; i.e., a transition in velocity decay processes occurs as the Reynolds number decreases. A supersonic core length is estimated from the streamwise distribution of the centerline velocity, and the length is then normalized by the nozzle exit height and plotted against the Reynolds number. As a result, it is found that the normalized supersonic core length attains a maximum value at a certain Reynolds number near which the transition in the velocity decay process occurs. 相似文献
11.
Three-dimensional (3D) trajectories of spherical air bubbles passing through a converging part of a rectangular channel have
been measured. Bubble diameters, d
b, were less than 1 mm and the Reynolds numbers, Re
b, for stagnant tapwater and for mean liquid velocity vˉ
L=0.25 m/s were in about same range.
Received: 15 January 2001 / Accepted: 12 June 2001 相似文献
12.
A. A. Maslov S. G. Mironov T. V. Poplavskaya I. S. Tsyryulnikov 《Journal of Applied Mechanics and Technical Physics》2010,51(4):482-488
A numerical and experimental study of receptivity of the viscous shock layer on a flat plate aligned at an angle of attack
to external acoustic perturbations is performed. Density and pressure fluctuations are measured in experiments at the free-stream
Mach number M
∞
= 21 and Reynolds number Re
1
= 6·10
5
m
−1
. Direct numerical simulations of receptivity of the viscous shock layer to external acoustic perturbations in wide ranges
of the governing parameters are performed by solving the Navier-Stokes equations with the use of high-order shock-capturing
schemes. The calculated intensities of density and pressure fluctuations are found to be in good agreement with experimental
data. Results of the study show that entropy-vortex disturbances dominate in the shock layer at small angles of attack, whereas
acoustic perturbations prevail at angles of attack above 20°. 相似文献
13.
The laminar flowfield in a rectangular channel immediately upstream of a hot film gradient probe with two parallel films was investigated in the range of Reynolds number Re
pr= 6 to 95, with the Reynolds number based on the probe diameter and the local flow velocity. For this study a photochromic dye flow visualization technique was used. The results show that the smaller the Reynolds number Re
prthe larger the influence of the probe is upon the flowfield. No distinct influence of the probe location relative to the channel walls on the flow deceleration process immediately upstream of the probe was observed.List of symbols
a
distance between the hot films
-
d
h
hydraulic diameter
-
d
pr
diameter of the probe body
-
Reynolds number based on hydraulic diameter and mean flow velocity
-
Reynolds number based on probe diameter and the undisturbed flow velocity at the centerline of probe
-
u
flow velocity in x-direction
-
u
0
undisturbed velocity in the center of the channel
-
undisturbed mean flow velocity
-
u(x,y)
velocity at position (x,y)
-
averaged velocity gradient
-
x
coordinate in main flow direction
-
y
coordinate normal to the larger wall of the rectangular channel
-
z
coordinate normal to x and y
-
v
kinematic viscosity 相似文献
14.
An experimental investigation was carried out to study the enhancement of the heat transfer from a heated flat plate fitted
with rectangular blocks of 1 × 2 × 2 cm3 dimensions in a channel flow as a function of Reynolds number (Reh), spacing (S
y
) of blocks in the flow direction, and the block orientation angle (α) with respect to the main flow direction. The experiments were performed in a channel of 18 cm width and 10 cm height, with
air as the working fluid. For fixed S
x
=3.81 cm, which is the space between the blocks in transverse to the flow direction, the experimental ranges of the parameters
were S
y
=3.33–4.33 cm, α=0–45°, Reh=7625–31550 based on the hydraulic diameter and the average velocity at the beginning of the test section in the channel.
Correlations for Nusselt number were developed, and the ratios of heat transfer with blocks to those with no blocks were given.
The results indicated that the heat transfer could be enhanced or reduced depending on the spacing between blocks, and the
block orientation angle. The maximum heat transfer rate was obtained at the orientation angle of 45°.
Received on 13 December 2000 / Published online: 29 November 2001 相似文献
15.
We establish the existence and stability of multidimensional steady transonic flows with transonic shocks through an infinite
nozzle of arbitrary cross-sections, including a slowly varying de Laval nozzle. The transonic flow is governed by the inviscid
potential flow equation with supersonic upstream flow at the entrance, uniform subsonic downstream flow at the exit at infinity,
and the slip boundary condition on the nozzle boundary. Our results indicate that, if the supersonic upstream flow at the
entrance is sufficiently close to a uniform flow, there exists a solution that consists of a C
1,α subsonic flow in the unbounded downstream region, converging to a uniform velocity state at infinity, and a C
1,α multidimensional transonic shock separating the subsonic flow from the supersonic upstream flow; the uniform velocity state
at the exit at infinity in the downstream direction is uniquely determined by the supersonic upstream flow; and the shock
is orthogonal to the nozzle boundary at every point of their intersection. In order to construct such a transonic flow, we
reformulate the multidimensional transonic nozzle problem into a free boundary problem for the subsonic phase, in which the
equation is elliptic and the free boundary is a transonic shock. The free boundary conditions are determined by the Rankine–Hugoniot
conditions along the shock. We further develop a nonlinear iteration approach and employ its advantages to deal with such
a free boundary problem in the unbounded domain. We also prove that the transonic flow with a transonic shock is unique and
stable with respect to the nozzle boundary and the smooth supersonic upstream flow at the entrance. 相似文献
16.
The flow and heat transfer in an inclined and horizontal rectangular duct with a heated plate longitudinally mounted in the
middle of cross section was experimentally investigated. The heated plate and rectangular duct were both made of highly conductive
materials, and the heated plate was subjected to a uniform heat flux. The heat transfer processes through the test section
were under various operating conditions: Pr ≈ 0.7, inclination angle ϕ = −60° to +60°, Reynolds number Re = 334–1,911, Grashof number Gr = 5.26 × 102–5.78 × 106. The experimental results showed that the average Nusselt number in the entrance region was 1.6–2 times as large as that
in the fully developed region. The average Nusselt numbers and pressure drops increased with the Reynolds number. The average
Nusselt numbers and pressure drops decreased with an increase in the inclination angle from −60° to +60° when the Reynolds
number was less than 1,500. But when the Reynolds number increased to over about 1,800, the heat transfer coefficients and
pressure drops were independent of inclination angles. 相似文献
17.
The adverse pressure gradient induced by a surface-mounted obstacle in a turbulent boundary layer causes the approaching flow
to separate and form a dynamically rich horseshoe vortex system (HSV) in the junction of the obstacle with the wall. The Reynolds
number of the flow (Re) is one of the important parameters that control the rich coherent dynamics of the vortex, which are known to give rise to
low-frequency, bimodal fluctuations of the velocity field (Devenport and Simpson, J Fluid Mech 210:23–55, 1990; Paik et al., Phys Fluids 19:045107, 2007). We carry out detached eddy simulations (DES) of the flow past a circular cylinder mounted on a rectangular channel for
Re = 2.0 × 104 and 3.9 × 104 (Dargahi, Exp Fluids 8:1–12, 1989) in order to systematically investigate the effect of the Reynolds number on the HSV dynamics. The computed results are compared
with each other and with previous experimental and computational results for a related junction flow at a much higher Reynolds
number (Re = 1.15 × 105) (Devenport and Simpson, J Fluid Mech 210:23–55, 1990; Paik et al., Phys Fluids 19:045107, 2007). The computed results reveal significant variations with Re in terms of the mean-flow quantities, turbulence statistics, and the coherent dynamics of the turbulent HSV. For Re = 2.0 × 104 the HSV system consists of a large number of necklace-type vortices that are shed periodically at higher frequencies than
those observed in the Re = 3.9 × 104 case. For this latter case the number of large-scale vortical structures that comprise the instantaneous HSV system is reduced
significantly and the flow dynamics becomes quasi-periodic. For both cases, we show that the instantaneous flowfields are
dominated by eruptions of wall-generated vorticity associated with the growth of hairpin vortices that wrap around and disorganize
the primary HSV system. The intensity and frequency of these eruptions, however, appears to diminish rapidly with decreasing
Re. In the high Re case the HSV system consists of a single, highly energetic, large-scale necklace vortex that is aperiodically disorganized
by the growth of the hairpin mode. Regardless of the Re, we find pockets in the junction region within which the histograms of velocity fluctuations are bimodal as has also been
observed in several previous experimental studies. 相似文献
18.
The flow developing downstream of a step change from smooth to rough surface condition is studied in the light of Townsend’s
wall similarity hypothesis. Previous studies seem to support the hypothesis for channel and pipe flows, but there are considerable
controversies about its application to boundary layers and in particular to surface roughness formed by spanwise bars. It
has been suggested that this controversy arises from insufficient separation of scales between the boundary layer thickness
and the roughness length scale. An experimental investigation has therefore been undertaken where the flow evolves from a
fully developed smooth wall boundary layer at high Reynolds numbers over a step in surface roughness (Re
θ = 13,400 at the step). The flow is mapped through the development of the internal layer until the flow is fully developed
over the rough wall. The internal layer is found to grow as δ ∼ X
0.73, and after about 15 boundary layer thicknesses at the step, the internal layer has reached the outer edge of the incoming
layer. At the last rough wall measurement station, the Reynolds number has grown to Re
θ ≈ 32,600 and the ratio of boundary layer to roughness length scales is δ/k ≈ 140. The outer layer differences between the smooth and the rough wall data were found to be sufficiently small to conclude
that for this setup the Townsend’s wall similarity hypothesis appears to hold. 相似文献
19.
Experimental data for a two-dimensional (2-D) turbulent boundary layer (TBL) flow and a three-dimensional (3-D) pressure-driven
TBL flow outside of a wing/body junction were obtained for an approach Reynolds number based on momentum thickness of Re
θ
=23,200. The wing shape had a 3:2 elliptical nose, NACA 0020 profiled tail, and was mounted on a flat wall. Some Reynolds
number effects are examined using fine spatial resolution (Δy
+=1.8) three-velocity-component laser-Doppler velocimeter measurements of mean velocities and Reynolds stresses at nine stations
for Re
θ
=23,200 and previously reported data for a much thinner boundary layer at Re
θ
=5,940 for the same wing shape. In the 3-D boundary layers, while the stress profiles vary considerably along the flow due
to deceleration, acceleration, and skewing, profiles of the parameter
correlate well and over available Reynolds numbers. The measured static pressure variations on the flat wall are similar
for the two Reynolds numbers, so the vorticity flux and the measured mean velocities scaled on wall variables agree closely
near the wall. The stresses vary similarly for both cases, but with higher values in the outer region of the higher Re
θ
case. The outer layer turbulence in the thicker high Reynolds number case behaves similarly to a rapid distortion of the
flow, since stream-wise vortical effects from the wall have not diffused completely through the boundary layer at all measurement
stations.
Received: 9 June 2000/Accepted: 26 January 2001 相似文献
20.
To establish the influence of the unit Reynolds number on the transition of a boundary layer on the side surface of a cone, the transition was investigated on a model of a sharp cone with half-angle = 7.5 ° and lengths from 150 to 400 mm. The experiments were made in a shock tube at Mach number M = 6.1 in the wide range of Reynolds numbers ReeL = 1.3·106-5.5·107. The position of the transition region was determined from the results of measurement of the local heat flux by calorimetric thermocouple converters. Data were obtained on the influence on the transition of the unit Reynolds number at large values. It was also shown that under the investigated conditions the base region does not influence the transition of the boundary layer on the surface of the cone.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 32–38, July–August, 1982. 相似文献