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1.
A wing in the form of a rectangular flat plate is subjected to periodic flapping motion. Space–time imaging provides quantitative
representations of the flow structure along the wing. Regions of spanwise flow exist along the wing surface; and depending
on the location along the span, the flow is either toward or away from the tip of the wing. Onset and development of large-scale,
streamwise-oriented vortical structures occur at locations inboard of the tip of the wing, and they can attain values of circulation
of the order of one-half the circulation of the tip vortex. Time-shifted images indicate that these streamwise vortical structures
persist over a major share of the wing chord. Space–time volume constructions define the form and duration of these structures,
relative to the tip vortex. 相似文献
2.
Andrew H. Lind Tejaswi Jarugumilli Moble Benedict Vinod K. Lakshminarayan Anya R. Jones Inderjit Chopra 《Experiments in fluids》2014,55(12):1-17
This paper examines the flow physics and principles of force production on a cycloidal rotor (cyclorotor) in forward flight. The cyclorotor considered here consists of two blades rotating about a horizontal axis, with cyclic pitch angle variation about the blade quarter-chord. The flow field at the rotor mid-span is analyzed using smoke flow visualization and particle image velocimeV are compared with flow fields predicted using 2D CFD and time-averaged force measurements acquired in an open-jet wind tunnel at three advance ratios. It is shown that the experimental flow field is nearly two dimensional at μ = 0.73 allowing for qualitative comparisons to be made with CFD. The incoming flow velocity decreases in magnitude as the flow passes through the retreating (upper) half of the rotor and is attributed to power extraction by the blades. A significant increase in flow velocity is observed across the advancing (lower) half of the rotor. The aerodynamic analysis demonstrates that the blades accelerate the flow through the lower aft region of the rotor, where they operate in a high dynamic pressure environment. This is consistent with CFD-predicted values of instantaneous aerodynamic forces which reveal that the aft section of the rotor is the primary region of force production. Phase-averaged flow field measurements showed two blade wakes in the flow, formed by each of the two blades. Analysis of the blades at several azimuthal positions revealed two significant blade-wake interactions. The locations of these blade-wake interactions are correlated with force peaks in the CFD-predicted instantaneous blade forces and highlight their importance to the generation of lift and propulsive force of the cyclorotor. 相似文献
3.
Flow in the rotors of wind turbines with a vertical axis of the Darrieus-Savonius type and their combinations is considered within the framework of the Navier-Stokes equations, in the two-dimensional formulation. A parametric investigation of the Darrieus rotor characteristics is carried out. For all configurations the dependence of the moment and power coefficients on the specific speed of the rotor is calculated. The possibility of the Darrieus rotor self- starting from the state of rest is investigated. The effect of nonmonotonicmoment variation for the Darrieus-type rotor is studied for the specific speeds of 0.5 to 1. A combined design of the Darrieus-Savonius rotor is considered to solve the problems due to a small moment of the Darrieus rotor during the start. 相似文献
4.
N. F. Vorob'ev 《Journal of Applied Mechanics and Technical Physics》1998,39(3):399-403
The inverse problem of wing aerodynamics—the determination of the lifting surface shape from a specified load—is solved within
the framework of linear theory. Volterra's solution of the wave equation is used. Solutions are found in the class of bounded
functions if certain conditions imposed on the governing parameters of the problem are satisfied. Solutions of inverse problems
of supersonic flow are presented for an infinite-span wing, a triangular wing with completely subsonic edges, and a rectangular
wing.
Institute of Theoretical and Applied Mechanics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated
from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 39, No. 3, pp. 86–91, May–June, 1998. 相似文献
5.
On the basis of experimental wind tunnel research, a topological classification of possible delta wing flow regimes is given
and a diagram in angle of attack-sweep angle coordinates is constructed. A regime with two pairs of symmetrically disposed
whirlwind like vortices formed on the surface of the wing is detected. The effect of the V-shape of the wing is considered.
Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.2, pp. 161–164, March–April, 1994. 相似文献
6.
G. N. Dudin 《Fluid Dynamics》1998,33(4):512-518
The influence of intense surface cooling on the parameters of a laminar boundary layer flow on a thin delta wing in a hypersonic
viscous perfect-gas stream is studied for the strong viscous-inviscid interaction regime. The effect of the power-law shape
of the wing cross-section and the wing thickness to boundary-layer displacement thickness ratio on the local and total aerodynamic
characteristics is numerically investigated.
Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 4, pp. 57–64, July–August, 1998. 相似文献
7.
The forces acting on a swept wing in the presence of a vortex induced by a delta wing, as well as the velocity field in the
vicinity of the swept wing, have been measured. By means of the “frozen,” vortex model and a specially-developed numerical
panel method, the forces and moments acting on the wing are calculated from the known velocity field. Comparison of the calculated
and measured force characteristics makes it possible to determine the extent to which the model fits the physical flow pattern.
It is shown that for the intense vortex considered in this study the model gives results which disagree sharply with the experimental
data.
Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 6, pp. 98–105, November–December,
1998.
The study was supported by the International Scientific and Technical Center under grant No. 201. 相似文献
8.
Three-dimensional near-wake structure behind a rotor was measured using slanted hot-wire technique in a large-scale, low-speed,
rotor/stator axial compressor. Unsteady flow interaction between blade rows was varied by setting the axial gap between rows
at 10% and 30% of rotor chord. Results show that stronger flow interactions between blade rows, or closer axial gap, produce
more pronounced time variation within the rotor wake. All parameters measured – three component velocities, yaw and pitch
angles – varied strongly within the wake, and are quantified.
Received: 8 July 1996/Accepted: 29 May 1997 相似文献
9.
A variational technique of obtaining the optimal shape of a low-aspect-ratio wing with allowance for the nonequilibrium character
of the flow is developed. The technique is applied to the problem of determining optimal wing shapes under terrestrial atmosphere
conditions. The real-gas effect on the optimal shapes and maximum lift-drag ratio is studied.
Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, pp. 160–170, March–April, 2000.
The study was carried out with the support of the Russian Foundation for Basic Research (project No. 96-01-00629). 相似文献
10.
This paper is motivated by the works of Dickinson et al. (Science 284:1954–1960, 1999) and Sun and Tang (J Exp Biol 205:55–70, 2002) which provided two different perspectives on the influence of wing–wake interaction (or wake capture) on lift generation
during flapping motion. Dickinson et al. (Science 284:1954–1960, 1999) hypothesize that wake capture is responsible for the additional lift generated at the early phase of each stroke, while Sun
and Tang (J Exp Biol 205:55–70, 2002) believe otherwise. Here, we take a more fundamental approach to study the effect of wing–wake interaction on the aerodynamic
force generation by carrying out simultaneous force and flow field measurements on a two-dimensional wing subjected to two
different types of motion. In one of the motions, the wing at a fixed angle of attack was made to follow a motion profile
described by “acceleration-constant velocity-deceleration”. Here, the wing was first linearly accelerated from rest to a predetermined
maximum velocity and remains at that speed for set duration before linearly decelerating to a stop. The acceleration and deceleration
phase each accounted for only 10% of the stroke, and the stroke covered a total distance of three chord lengths. In another
motion, the wing was subjected to the same above-mentioned movement, but in a back and forth manner over twenty strokes. Results
show that there are two possible outcomes of wing–wake interaction. The first outcome occurs when the wing encounters a pair
of counter-rotating wake vortices on the reverse stroke, and the induced velocity of these vortices impinges directly on the
windward side of the wing, resulting in a higher oncoming flow to the wing, which translates into a higher lift. Another outcome
is when the wing encounters one vortex on the reverse stroke, and the close proximity of this vortex to the windward surface
of the wing, coupled with the vortex suction effect (caused by low pressure region at the center of the vortex), causes the
net force on the wing to decrease momentarily. These results suggest that wing–wake interaction does not always lead to lift
enhancement, and it can also cause lift reduction. As to which outcome prevails depend very much on the flapping motion and
the timing of the reverse stroke. 相似文献
11.
The spatial-temporal progressions of the leading-edge stagnation, separation and reattachment points, and the state of the
unsteady boundary layer developed on the upper surface of a 6 in. chord NACA 0012 airfoil model, oscillated sinusoidally within
and beyond the static-stall angle, were measured using 140 closely-spaced, multiple hot-film sensors (MHFS). The MHFS measurements
show that (i) the laminar separation point and transition were delayed with increasing α and the reattachment and relaminarization
were promoted with decreasing α, relative to the static case, (ii) the pitchup motion helped to keep the boundary layer attached
to higher angles of attack over that could be obtained statically, (iii) the dynamic stall process was initiated by the turbulent
flow separation in the leading-edge region as well as by the onset of flow reversal in the trailing-edge region, and (iv) the
dynamic stall process was found not to originate with the bursting of a laminar separation bubble, but with a breakdown of
the turbulent boundary layer. The MHFS measurements also show that the flow unsteadiness caused by airfoil motion as well
as by the flow disturbances can be detected simultaneously and nonintrusively. The MHFS characterizations of the unsteady
boundary layers are useful in the study of unsteady separated flowfields generated by rapidly maneuvering aircraft, helicopter
rotor blades, and wing energy machines.
Received: 17 June 1997 / Accepted: 10 December 1997 相似文献
12.
A. A. F. Hashem Lecturer R. E. Peacock Senior Lecturer 《International Journal of Heat and Fluid Flow》1979,1(3):133-141
A technique is developed to assess the interdependent effects of an aerofoil in the vicinity of, immersed in or passing through, a shear flow. The two former cases in which there is no time-dependency are analogous to an aircraft wing and slipstream combination, while the latter case may be likened to a compressor rotor blade responding to a circumferential distortion. In the model, however, no time-dependent terms are included.A case study is made of an aerofoil of known geometry passing through a combined pressure/temperature distortion of stated initial geometry. The changes both in the streamline patterns of the distortion and of the pressure distribution are indicated and it is seen that the resulting lift response of the aerofoil bears some resemblance to that measured on rotating blades in compressors with circumferential flow conditions. 相似文献
13.
The three‐dimensional flow in a straight blade agitator with free surface on top is simulated using a grid‐free method named moving particle semi‐implicit method. The agitator has six rotor blades matched with six stationary guide blades. The mechanism and phenomena of the flow are investigated in the area between two adjacent stationary guide blades. Eddies near each tip of the rotational blades are predicted, and they move with the motion of the rotor blades but in opposite rotation direction of the rotor. The rotation axis of the eddies is traced and annular vortices, which are made by the eddies, are studied. The pressure pulsation in the rotation process is also predicted with this particle method. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
14.
D. N. Gorelov 《Journal of Applied Mechanics and Technical Physics》2007,48(2):184-191
A general formulation of a nonlinear initial-boundary problem of an unsteady separated flow around an airfoil by an ideal
incompressible fluid is considered. The problem is formulated for a complex velocity. Conditions of shedding of vortex wakes
from the airfoil are analyzed in detail. The proposed system of functional relations allows constructing algorithms for solving
a wide class of problems of the wing theory.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 2, pp. 48–56, March–April, 2007. 相似文献
15.
Oliver Schennach Jakob Woisetschläger Andreas Marn Emil Göttlich 《Experiments in fluids》2007,43(2-3):385-393
A one and a half stage transonic turbine was tested using a two component laser–doppler–velocimetry system. The measurements
were carried out in order to record rotor phase resolved velocity, flow angle and turbulence distributions upstream and downstream
of the second stator row at several different angular stator–stator positions (“clocking” positions). Altogether, the measurements
downstream of the second stator were performed for ten different clocking positions and upstream of the second stator for
two different clocking positions. These different clocking positions have a significant influence on the flow field upstream
and downstream of the second stator. Furthermore error estimation and a discussion of the tracer particle response are discussed. 相似文献
16.
The hydrodynamic interaction of three blade rows (stator, rotor, and stator) of an axial compressor in a subsonic flow is
investigated both theoretically and experimentally. It is established that the parameters of the time-dependent rotor flow
may significantly depend on the relative peripheral position of the stators. The theoretical and experimental results are
compared.
Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 3, pp. 145–158, May–June, 2000.
The study was carried out with the support of the Russian Foundation for Basic Research (project No. 96-01-01847) and the
USA Civil Research and Development Foundation (grant No. RE1-195). 相似文献
17.
The impact of 12 spoiler–tab configurations, of different heights and widths, on the tip vortex generated by an oscillating
NACA 0015 wing was investigated experimentally. For an oscillating wing equipped with a spoiler, the peak tangential velocity
and core and total circulation were greatly reduced compared to a tab, regardless of its width, while the core radius remained
largely unaffected with its center displaced vertically above the baseline wing. The most noticeable impact of a spoiler with
a reduced height was its potential in alleviating the blade–vortex interaction (BVI) strength. Meanwhile, the largest favorable
impact on the critical vortex flow parameters was achieved via a 25%-span spoiler–tab combination with a height of 5 and 2.5%
chord, respectively. A contrary effect on the BVI suppression, especially during pitch-up, was, however, observed. The impact
on the BVI can be improved by reducing the height of the spoiler at the expense of unfavorable change in the vortex strength
and displacement. 相似文献
18.
Fully suspended, five-axis, three-magnetic-bearing dynamic spin rig with forced excitation 总被引:2,自引:0,他引:2
C. R. Morrison A. Provenza A. Kurkov G. Montague K. Duffy O. Mehmed D. Johnson R. Jansen 《Experimental Mechanics》2005,45(3):226-237
A significant advancement in the dynamic spin rig (DSR), i.e., the five-axis, three-magnetic-bearing DSR, is used to perform
vibration tests of turbomachinery blades and components under rotating and non-rotating conditions in a vacuum. The rig has
three magnetic bearings as its critical components: two heteropolar radial active magnetic bearings and a magnetic thrust
bearing. The bearing configuration allows full vertical rotor magnetic suspension along with a feedforward control feature,
which enables the excitation of various modes of vibration in the bladed disk test articles. The theoretical, mechanical,
electrical, and electronic aspects of the rig are discussed. Also presented are the forced-excitation results of a fully levitated,
rotating and non-rotating, unbladed rotor and a fully levitated, rotating and non-rotating, bladed rotor in which a pair of
blades were arranged 180° apart from each other. These tests include the “bounce” mode excitation of the rotor in which the
rotor was excited at the blade natural frequency of 144 Hz. The rotor natural mode frequency of 355 Hz was discerned from
the plot of acceleration versus frequency. For non-rotating blades, a blade-tip excitation amplitude of approximately 100
g A−1 was achieved at the first-bending critical (≈144 Hz) and at the first-torsional and second-bending blade modes. A blade-tip
displacement of 1.778×10−3m (70 mils) was achieved at the first-bending critical by exciting the blades at a forced-excitation phase angle of 90° relative
to the vertical plane containing the blades while simultaneously rotating the shaft at 3000 rpm. 相似文献
19.
Large-Eddy Simulation is utilized to investigate the rotor–stator interaction within a centrifugal pump. Comparisons are presented across diffuser geometries for two values of the flow-rate. Decreasing the incidence angle on the diffuser blades at off-design is found the main source of higher pressure rise and lower overall values of turbulent kinetic energy within the pump, resulting in efficiency improvement. The impact on the second-order statistics of the flow is especially significant. However, the values of the pressure fluctuations acting on the diffuser blades, defining fatigue loads on them and cavitation phenomena, are found especially affected by the rotor–stator clearance. Results show that at reduced flow-rates the rotation of the diffuser blades around their mid camber is a better option than rotating them around their leading edge. They also suggest that at larger flow-rates the increased incidence on the diffuser blades causes pressure side separation and large shear layers populating the diffuser channels, not affecting substantially the region of interface between impeller and diffuser, but having detrimental effects on the performance of the latter. The rotation of the diffuser blades around their leading edge should be preferred when the pump operates at flow-rates larger than the design one, avoiding decreasing the rotor–stator gap, thus resulting in smoother rotor–stator interaction and lower pressure fluctuations. 相似文献
20.
N. V. Semionov Yu. G. Ermolaev A. D. Kosinov 《Journal of Applied Mechanics and Technical Physics》2008,49(2):188-193
Experimental data on stability of a three-dimensional supersonic boundary layer on a swept wing are presented. The experiments
are performed on a swept wing model with a lenticular profile with a 40° sweep angle of the leading edge at a zero angle of
attack. The supersonic boundary layer on the swept wing was laminarized with the use of distributed roughness. A pioneering
study of interaction of traveling and stationary disturbances is performed. Some specific features of this interaction are
identified. The main reason for turbulence emergence in a supersonic boundary layer on a swept wing is demonstrated to be
secondary crossflow instability.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 2, pp. 40–46, March–April, 2008. 相似文献