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1.
A NACA 0015 airfoil with and without a Gurney flap was studied in a wind tunnel with Re
c = 2.0 × 105 in order to examine the evolving flow structure of the wake through time-resolved PIV and to correlate this structure with time-averaged measurements of the lift coefficient. The Gurney flap, a tab of small length (1–4% of the airfoil chord) that protrudes perpendicular to the chord at the trailing edge, yields a significant and relatively constant lift increment through the linear range of the C
L
versus α curve. Two distinct vortex shedding modes were found to exist and interact in the wake downstream of flapped airfoils. The dominant mode resembles a Kàrmàn vortex street shedding behind an asymmetric bluff body. The second mode, which was caused by the intermittent shedding of fluid recirculating in the cavity upstream of the flap, becomes more coherent with increasing angle of attack. For a 4% Gurney flap at α = 8°, the first and second modes corresponded with Strouhal numbers based on flap height of 0.18 and 0.13. Comparison of flow around ‘filled’ and ‘open’ flap configurations suggested that the second shedding mode was responsible for a significant portion of the overall lift increment. 相似文献
2.
Miguel R. Visbal Raymond E. Gordnier Marshall C. Galbraith 《Experiments in fluids》2009,46(5):903-922
The present paper highlights results derived from the application of a high-fidelity simulation technique to the analysis
of low-Reynolds-number transitional flows over moving and flexible canonical configurations motivated by small natural and
man-made flyers. This effort addresses three separate fluid dynamic phenomena relevant to small fliers, including: laminar
separation and transition over a stationary airfoil, transition effects on the dynamic stall vortex generated by a plunging
airfoil, and the effect of flexibility on the flow structure above a membrane airfoil. The specific cases were also selected
to permit comparison with available experimental measurements. First, the process of transition on a stationary SD7003 airfoil
section over a range of Reynolds numbers and angles of attack is considered. Prior to stall, the flow exhibits a separated
shear layer which rolls up into spanwise vortices. These vortices subsequently undergo spanwise instabilities, and ultimately
breakdown into fine-scale turbulent structures as the boundary layer reattaches to the airfoil surface. In a time-averaged
sense, the flow displays a closed laminar separation bubble which moves upstream and contracts in size with increasing angle
of attack for a fixed Reynolds number. For a fixed angle of attack, as the Reynolds number decreases, the laminar separation
bubble grows in vertical extent producing a significant increase in drag. For the lowest Reynolds number considered (Re
c
= 104), transition does not occur over the airfoil at moderate angles of attack prior to stall. Next, the impact of a prescribed
high-frequency small-amplitude plunging motion on the transitional flow over the SD7003 airfoil is investigated. The motion-induced
high angle of attack results in unsteady separation in the leading edge and in the formation of dynamic-stall-like vortices
which convect downstream close to the airfoil. At the lowest value of Reynolds number (Re
c
= 104), transition effects are observed to be minor and the dynamic stall vortex system remains fairly coherent. For Re
c
= 4 × 104, the dynamic-stall vortex system is laminar at is inception, however shortly afterwards, it experiences an abrupt breakdown
associated with the onset of spanwise instability effects. The computed phased-averaged structures for both values of Reynolds
number are found to be in good agreement with the experimental data. Finally, the effect of structural compliance on the unsteady
flow past a membrane airfoil is investigated. The membrane deformation results in mean camber and large fluctuations which
improve aerodynamic performance. Larger values of lift and a delay in stall are achieved relative to a rigid airfoil configuration.
For Re
c
= 4.85 × 104, it is shown that correct prediction of the transitional process is critical to capturing the proper membrane structural
response. 相似文献
3.
Y. Zhou Md. Mahbub Alam H.X. YangH. Guo D.H. Wood 《International Journal of Heat and Fluid Flow》2011,32(1):329-339
This paper presents the measurements of mean and fluctuating forces on an NACA0012 airfoil over a large range of angle (α) of attack (0-90°) and low to small chord Reynolds numbers (Rec), 5.3 × 103-5.1 × 104, which is of both fundamental and practical importance. The forces, measured using a load cell, display good agreement with the estimate from the LDA-measured cross-flow distributions of velocities in the wake based on the momentum conservation. The dependence of the forces on both α and Rec is determined and discussed in detail. It has been found that the stall of an airfoil, characterized by a drop in the lift force and a jump in the drag force, occurs at Rec ? 1.05 × 104 but is absent at Rec = 5.3 × 103. A theoretical analysis is developed to predict and explain the observed dependence of the mean lift and drag on α. 相似文献
4.
The near-field flow structure of a tip vortex behind a sweptback and tapered NACA 0015 wing was investigated and compared
with a rectangular wing at the same lift force and Re=1.81×105. The tangential velocity decreased with the downstream distance while increased with the airfoil incidence. The core radius
was about 3% of the root chord c
r, regardless of the downstream distance and α for α<8°. The core axial velocity was always wake-like. The core Γc and total Γo circulation of the tip vortex remained nearly constant up to x/c
r=3.5 and had a Γc/Γo ratio of 0.63. The total circulation of the tip vortex accounted for only about 40% of the bound root circulation Γb. For a rectangular wing, the axial flow exhibited islands of wake- and jet-like velocity distributions with Γc/Γo=0.75 and Γo/Γb=0.70. For the sweptback and tapered wing tested, the inner region of the tip vortex flow exhibited a self-similar behavior
for x/c
r≥1.0. The lift force computed from the spanwise circulation distributions agreed well with the force-balance data. A large
difference in the lift-induced drag was, however, observed between the wake integral method and the inviscid lifting-line
theory. 相似文献
5.
The passage of solid spheres through a liquid–liquid interface was experimentally investigated using a high-speed video and
PIV (particle image velocimetry) system. Experiments were conducted in a square Plexiglas column of 0.1 m. The Newtonian Emkarox
(HV45 50 and 65% wt) aqueous solutions were employed for the dense phase, while different silicone oils of different viscosity
ranging from 10 to 100 mPa s were used as light phase. Experimental results quantitatively reveal the effect of the sphere’s
size, interfacial tension and viscosity of both phases on the retaining time and the height of the liquid entrained behind
the sphere. These data were combined with our previous results concerning the passage of a rising bubble through a liquid–liquid
interface in order to propose a general relationship for the interface breakthrough for the wide range of Mo
1/Mo
2 ∈ [2 × 10−5–5 × 104] and Re
1/Re
2 ∈ [2 × 10−3–5 × 102]. 相似文献
6.
This paper reports results of DPIV measurements on a two-dimensional elliptic airfoil rotating about its own axis of symmetry
in a fluid at rest and in a parallel freestream. In the former case, we examined three rotating speeds (Re
c,Ω = 400, 1,000 and 2,000), and in the later case, four rotating speeds (Ro
c,Ω = 2.4, 1.2, 0.6 and 0.4), together with two freestream velocities (Re
c,u
= 200 and 1,000) and two starting configurations of the airfoil (i.e., chord parallel to (α
0 = 0°) or normal (α
0 = 90°) to the freestream). Results show that a rotating airfoil in a stationary fluid produces two distinct types of vortex
structures depending on the Reynolds number. The first type occurs at the lowest Reynolds number (Re
c,Ω = 400), where vortices shed from the two edges or tips of the airfoil dissipated quickly, resulting in the airfoil rotating
in a layer of diffused vorticity. The second type occurs at higher Reynolds numbers (i.e., Re
c,Ω = 1,000 and 2,000), where the corresponding vortices rotated together with the airfoil. Due to the vortex suction effect,
the torque characteristics are likely to be heavily damped for the first type because of the rapidly subsiding vortex shedding,
and more oscillatory for the second type due to persistent presence of tip vortices. In a parallel freestream, increasing
the tip-speed ratio (V/U) of the airfoil (i.e., decreasing the Rossby number, Ro
c,Ω) transformed the flow topology from periodic vortex shedding at Ro
c,Ω = 2.4 to the generation of a “hovering vortex” at Ro
c,Ω = 0.6 and 0.4. The presence of the hovering vortex, which has not been reported in literature before, is likely to enhance
the lift characteristics of the airfoil. Freestream Reynolds number is found to have minimal effect on the vortex formation
and shedding process, although it enhances shear layer instability and produces more small-scale flow structures that affect
the dynamics of the hovering vortex. Likewise, initial starting configuration of the airfoil, while affecting the flow transient
during the initial phase of rotation, has insignificant effect on the overall flow topology. Unfortunately, technical constraint
of our apparatus prevented us from carrying out complimentary force measurements; nevertheless, the results presented herein,
which are more extensive than those computed by Lugt and Ohring (1977), will provide useful benchmark data, from which more advanced numerical calculations can be carried out to ascertain the
corresponding force characteristics, particularly for those conditions with the presence of hovering vortex. 相似文献
7.
A stochastic estimation technique has been applied to simultaneously acquired data of velocity and surface pressure as a tool
to identify the sources of wall-pressure fluctuations. The measurements have been done on a NACA0012 airfoil at a Reynolds
number of Re
c
= 2 × 105, based on the chord of the airfoil, where a separated laminar boundary layer was present. By performing simultaneous measurements
of the surface pressure fluctuations and of the velocity field in the boundary layer and wake of the airfoil, the wall-pressure
sources near the trailing edge (TE) have been studied. The mechanisms and flow structures associated with the generation of
the surface pressure have been investigated. The “quasi-instantaneous” velocity field resulting from the application of the
technique has led to a picture of the evolution in time of the convecting surface pressure generating flow structures and
revealed information about the sources of the wall-pressure fluctuations, their nature and variability. These sources are
closely related to those of the radiated noise from the TE of an airfoil and to the vibration issues encountered in ship hulls
for example. The NACA0012 airfoil had a 30 cm chord and aspect ratio of 1. 相似文献
8.
In order to evaluate characteristics of the liquid film flow and their influences on heat and mass transfer, measurements
of the instantaneous film thickness using a capacitance method and observation of film breakdown are performed. Experimental
results are reported in the paper. Experiments are carried out at Re = 250–10000, T
in = 20–50°C and three axial positions of vertically falling liquid films for film thickness measurements. Instantaneous surface
waveshapes are given by the interpretation of the test data using the cubic spline method. The correlation of the mean film
thickness versus the film Reynolds number is also given by fitting the test data. It is revealed that the surface wave has
nonlinear behavior. Observation of film breakdown is performed at Re = 1.40 × 103–1.75 × 104 and T
in = 85–95°C. From experimental results, the correlation of the film breakdown criterion can be obtained as follows: Bd = 1.567 × 10−6
Re
1.183 相似文献
9.
This paper reports the results of an experimental investigation on a two-dimensional (2-D) wing undergoing symmetric simple
harmonic flapping motion. The purpose of this investigation is to study how flapping frequency (or Reynolds number) and angular
amplitude affect aerodynamic force generation and the associated flow field during flapping for Reynolds number (Re) ranging from 663 to 2652, and angular amplitudes (α
A) of 30°, 45° and 60°. Our results support the findings of earlier studies that fluid inertia and leading edge vortices play
dominant roles in the generation of aerodynamic forces. More importantly, time-resolved force coefficients during flapping
are found to be more sensitive to changes in α
A than in Re. In fact, a subtle change in α
A may lead to considerable changes in the lift and drag coefficients, and there appears to be an optimal mean lift coefficient
around α
A = 45°, at least for the range of flow parameters considered here. This optimal condition coincides with the development a
reverse Karman Vortex street in the wake, which has a higher jet stream than a vortex dipole at α
A = 30° and a neutral wake structure at α
A = 60°. Although Re has less effect on temporal force coefficients and the associated wake structures, increasing Re tends to equalize mean lift coefficients (and also mean drag coefficients) during downstroke and upstroke, thus suggesting
an increasing symmetry in the mean force generation between these strokes. Although the current study deals with a 2-D hovering
motion only, the unique force characteristics observed here, particularly their strong dependence on α
A, may also occur in a three-dimensional hovering motion, and flying insects may well have taken advantage of these characteristics
to help them to stay aloft and maneuver.
An erratum to this article can be found at 相似文献
10.
The impact of Gurney flaps (GF), of different heights and perforations, on the aerodynamic and wake characteristics of a NACA
0015 airfoil equipped with a trailing-edge flap (TEF) was investigated experimentally at Re = 2.54 × 105. The addition of the Gurney flap to the TEF produced a further increase in the downward turning of the mean flow (increased
aft camber), leading to a significant increase in the lift, drag, and pitching moment compared to that produced by independently
deployed TEF or GF. The maximum lift increased with flap height, with the maximum lift-enhancement effectiveness exhibited
at the smallest flap height. The near wake behind the joint TEF and GF became wider and had a larger velocity deficit and
fluctuations compared to independent GF and TEF deployment. The Gurney flap perforation had only a minor impact on the wake
and aerodynamics characteristics compared to TEF with a solid GF. The rapid rise in lift generation of the joint TEF and GF
application, compared to conventional TEF deployment, could provide an improved off-design high-lift device during landing
and takeoff. 相似文献
11.
Davide Lasagna Raffaele Donelli Fabrizio De Gregorio Gaetano Iuso 《Experiments in fluids》2011,51(5):1369-1384
The effects of a trapped vortex cell (TVC) on the aerodynamic performance of a NACA0024 wing model were investigated experimentally
at Re = 106 and 6.67×1056.67\times 10^{5}. The static pressure distributions around the model and the wake velocity profiles were measured to obtain lift and drag
coefficients, for both the clean airfoil and the controlled configurations. Suction was applied in the cavity region to stabilize
the trapped vortex. For comparison, a classical boundary layer suction configuration was also tested. The drag coefficient
curve of the TVC-controlled airfoil showed sharp discontinuities and bifurcative behavior, generating two drag modes. A strong
influence of the angle of attack, the suction rate and the Reynolds number on the drag coefficient was observed. With respect
to the clean airfoil, the control led to a drag reduction only if the suction was high enough. Compared to the classical boundary
layer suction configuration, the drag reduction was higher for the same amount of suction only in a specific range of incidence,
i.e., α = −2° to α = 6° and only for the higher Reynolds number. For all the other conditions, the classical boundary layer
suction configuration gave better drag performances. Moderate increments of lift were observed for the TVC-controlled airfoil
at low incidence, while a 20% lift enhancement was observed in the stall region with respect to the baseline. However, the
same lift increments were also observed for the classical boundary layer suction configuration. Pressure fluctuation measurements
in the cavity region suggested a very complex interaction of several flow features. The two drag modes were characterized
by typical unsteady phenomena observed in rectangular cavity flows, namely the shear layer mode and the wake mode. 相似文献
12.
An experimental study of a bio-inspired corrugated airfoil for micro air vehicle applications 总被引:1,自引:0,他引:1
An experimental study was conducted to investigate the aerodynamic characteristics of a bio-inspired corrugated airfoil compared
with a smooth-surfaced airfoil and a flat plate at the chord Reynolds number of Re
C
= 58,000–125,000 to explore the potential applications of such bio-inspired corrugated airfoils for micro air vehicle designs.
In addition to measuring the aerodynamic lift and drag forces acting on the tested airfoils, a digital particle image velocimetry
system was used to conduct detailed flowfield measurements to quantify the transient behavior of vortex and turbulent flow
structures around the airfoils. The measurement result revealed clearly that the corrugated airfoil has better performance
over the smooth-surfaced airfoil and the flat plate in providing higher lift and preventing large-scale flow separation and
airfoil stall at low Reynolds numbers (Re
C
< 100,000). While aerodynamic performance of the smooth-surfaced airfoil and the flat plate would vary considerably with
the changing of the chord Reynolds numbers, the aerodynamic performance of the corrugated airfoil was found to be almost insensitive
to the Reynolds numbers. The detailed flow field measurements were correlated with the aerodynamic force measurement data
to elucidate underlying physics to improve our understanding about how and why the corrugation feature found in dragonfly
wings holds aerodynamic advantages for low Reynolds number flight applications. 相似文献
13.
The flow behind perforated Gurney-type flaps was investigated by using particle image velocimetry (PIV) at Re = 5.3 × 104. The PIV measurements were supplemented by force balance and surface pressure data. The near wake was disrupted and narrowed,
indicative of a reduced drag, with increasing flap perforation and had a drastically suppressed fluctuating intensity. Depending
on the strength of the perforation-generated jet, the vortex shedding process behind the flap could be eliminated. The flap
porosity also led to reduced positive camber effects and the decompression of the cavity flow (upstream of the flap), as well
as decreased upper and lower surface pressures, compared to the solid flap. The reduction in the drag, however, outweighed
the loss in lift and rendered an improved lift-to-drag ratio. 相似文献
14.
Experiments have been made to measure some of the near wake properties of axisymmetric bluff body flows with fixed points
of separation, including the detention or residence time of fluid borne scalar entities, base pressure coefficient, wake bubble
length parameter and shape parameter. Measurements were made in smooth and turbulent air flow for Reynolds number in the range
2×103<Re<4×104. The results for a given bluff body were found to be uniquely controlled by a free-stream turbulence parameter. The data
for all the shapes of bluff body in the class under consideration were found to collapse into unique inter-relationships by
the introduction of the face pressure coefficient as a quantitative measure of “bluffness”.
This paper was originally presented at the 14th International Congress of Theoretical and Applied Mechanics, Delft (August–September,
1976). 相似文献
15.
Particle image velocimetry and smoke visualization are used to study the alteration of the flow field in the wake of a bluff body by use of an alternating current (AC) surface dielectric barrier discharge. Staggered, surface, and buried electrodes were positioned on the downstream side of circular cylinders at conditions of Re
D
= 1 × 104−4 × 104 configured to impose a force due to the ion drift that is either along or counter to the free-stream flow direction. Smoke visualization and Particle Image Velocimetry (PIV) in the wake of the flow confirms that the configuration of the surface electrodes and operation of the discharge significantly alters the location of the flow separation point and the time-averaged velocity profiles in the near and distant wake. Measurements of the vibrational and the rotational temperature using optical emission spectroscopy on the N2 second positive system (C3Πu–B3Πg) indicates that the resulting plasma is highly non-equilibrium and discounts the possibility of a thermal effect on the flow separation process. The mechanism responsible for reduction or enhancement of flow separation is attributed to the streamwise force generated by the asymmetric ion wind—the direction of which is established by the electrode geometry and the local surface charge accumulated on AC cycles. 相似文献
16.
Investigation of the vortex induced unsteadiness of a separation bubble via time-resolved and scanning PIV measurements 总被引:1,自引:0,他引:1
A transitional separation bubble on the suction side of an SD7003 airfoil is considered. The transition process that forces
the separated shear layer to reattach seems to be governed by Kelvin–Helmholtz instabilities. Large scale vortices are formed
due to this mechanism at the downstream end of the bubble. These vortices possess a three-dimensional structure and detach
from the recirculation region, while other vortices are formed within the bubble. This separation of the vortex is a highly
unsteady process, which leads to a bubble flapping. The structure of these vortices and the flapping of the separation bubble
due to these vortices are temporally and spatially analyzed at angles of attack from 4° to 8° and chord-length based Reynolds
numbers Re
c = 20,000–60,000 using time-resolved PIV measurements in a 2D and a 3D set-up, i.e., stereo-scanning PIV measurements are
done in the latter case. These measurements complete former studies at a Reynolds number of Re
c = 20,000. The results of the time-resolved PIV measurements in a single light-sheet show the influence of the angle of attack
and the Reynolds number. The characteristic parameters of the separation bubble are analyzed focusing on the unsteadiness
of the separation bubble, e.g., the varying size of the main recirculation region, which characterizes the bubble flapping,
and the corresponding Strouhal number are investigated. Furthermore, the impact of the freestream turbulence is investigated
by juxtaposing the current and former results. The stereo-scanning PIV measurements at Reynolds numbers up to 60,000 elucidate
the three-dimensional character of the vortical structures, which evolve at the downstream end of the separation bubble. It
is shown that the same typical structures are formed, e.g., the c-shape vortex and the screwdriver vortex at each Reynolds
number and angle of attack investigated and the occurrence of these patterns in relation to Λ-structures is discussed. To
evidence the impact of the freestream turbulence, these results are compared with findings of former measurements. 相似文献
17.
Nadina Müller-Fischer Philip Tobler Marco Dressler Peter Fischer Erich J. Windhab 《Experiments in fluids》2008,45(5):917-926
Experiments in a parallel band apparatus and a transparent concentric cylinder device allow the observation of bubble deformation
(shape and orientation) and breakup as a function of the viscosity ratio λ and the Capillary number Ca. For viscosity ratios between 3.1 × 10−7 and 6.7 × 10−8, critical Capillary numbers Ca
c for bubble breakup between 29 and 45 are found. It is furthermore shown that in the given parameter space no clear distinction
between tip breakup and fracture can be made for bubbles.
An erratum to this article can be found at 相似文献
18.
Flap-bounding is a common flight style in small birds in which flapping phases alternate with flexed-wing bounds. Body lift
is predicted to be essential to making this flight style an aerodynamically attractive flight strategy. To elucidate the contributions
of the body and tail to lift and drag during the flexed-wing bound phase, we used particle image velocimetry (PIV) and measured
properties of the wake of zebra finch (Taeniopygia guttata, N = 5), flying at 6–10 m s−1 in a variable speed wind tunnel as well as flow around taxidermically prepared specimens (N = 4) mounted on a sting instrumented with force transducers. For the specimens, we varied air velocity from 2 to 12 m s−1 and body angle from −15° to 50°. The wake of bounding birds and mounted specimens consisted of a pair of counter-rotating
vortices shed into the wake from the tail, with induced downwash in the sagittal plane and upwash in parasagittal planes lateral
to the bird. This wake structure was present even when the tail was entirely removed. We observed good agreement between force
measures derived from PIV and force transducers over the range of body angles typically used by zebra finch during forward
flight. Body lift:drag (L:D) ratios averaged 1.4 in live birds and varied between 1 and 1.5 in specimens at body angles from 10° to 30°. Peak (L:D) ratio was the same in live birds and specimens (1.5) and was exhibited in specimens at body angles of 15° or 20°, consistent
with the lower end of body angles utilized during bounds. Increasing flight velocity in live birds caused a decrease in C
L
and C
D
from maximum values of 1.19 and 0.95 during flight at 6 m s−1 to minimum values of 0.70 and 0.54 during flight at 10 m s−1. Consistent with delta-wing theory as applied to birds with a graduated-tail shape, trimming the tail to 0 and 50% of normal
length reduced L:D ratios and extending tail length to 150% of normal increased L:D ratio. As downward induced velocity is present in the sagittal plane during upstroke of flapping flight, we hypothesize that
body lift is produced during flapping phases. Future efforts to model the mechanics of intermittent flight should take into
account that flap-bounding birds may support up to 20% of their weight even with their wings fully flexed. 相似文献
19.
G. H. Keetels W. Kramer H. J. H. Clercx G. J. F. van Heijst 《Theoretical and Computational Fluid Dynamics》2011,25(5):293-300
Recently, numerical studies revealed two different scaling regimes of the peak enstrophy Z and palinstrophy P during the collision of a dipole with a no-slip wall [Clercx and van Heijst, Phys. Rev. E 65, 066305, 2002]: Z μ Re0.8{Z\propto{\rm Re}^{0.8}} and P μ Re2.25{P\propto {\rm Re}^{2.25}} for 5 × 102 ≤ Re ≤ 2 × 104 and Z μ Re0.5{Z\propto{\rm Re}^{0.5}} and P μ Re1.5{P\propto{\rm Re}^{1.5}} for Re ≥ 2 × 104 (with Re based on the velocity and size of the dipole). A critical Reynolds number Re
c
(here, Rec ? 2×104{{\rm Re}_c\approx 2\times 10^4}) is identified below which the interaction time of the dipole with the boundary layer depends on the kinematic viscosity
ν. The oscillating plate as a boundary-layer problem can then be used to mimick the vortex-wall interaction and the following
scaling relations are obtained: Z μ Re3/4, P μ Re9/4{Z\propto{\rm Re}^{3/4}, P\propto {\rm Re}^{9/4}} , and dP/dt μ Re11/4{\propto {\rm Re}^{11/4}} in agreement with the numerically obtained scaling laws. For Re ≥ Re
c
the interaction time of the dipole with the boundary layer becomes independent of the kinematic viscosity and, applying flat-plate
boundary-layer theory, this yields: Z μ Re1/2{Z\propto{\rm Re}^{1/2}} and P μ Re3/2{P\propto {\rm Re}^{3/2}}. 相似文献
20.
Kévin Gosse Béatrice Patte-Rouland Michel Gonzalez Pierre Paranthoën 《Experiments in fluids》2006,40(1):135-140
Experimental results on tracer gas diffusion within the near wake of a simplified model car (Ahmed model with a rear slant
angle of 25°) are presented. Pollutant emission is simulated using heated air injected through a small pipe at one side of
the model base. Fine cold wire thermometry is used to measure instantaneous temperature excess in the near wake. Characteristics
of the temperature field over the Reynolds number range (1.3×104<Re
L<7×104) show strong differences as a result of transition in the wake at a critical Reynolds number Re
Lc=2.7×104. 相似文献