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1.
A. Liakopoulos 《国际流体数值方法杂志》1985,5(1):81-97
The applicability of a finite element-differential method to the computation of steady two-dimensional low-speed, transonic and supersonic turbulent boundary-layer flows is investigated. The turbulence model chosen for the Reynolds shear stress and turbulent heat flux is the K-? two-equation model. Calculations are extended up to the wall and the exact values of the dependent variables at the wall are used as boundary conditions. A number of transformations are carried out and the assumed solutions at a longitudinal station are represented by complete cubic spline functions. In essence, the method converts the governing partial differential equations into a system of ordinary differential equations by a weighted residuals method and invokes an ordinary differential equation solver for the numerical integration of the reduced initial-value problem. The results of the computations reveal that the method is highly accurate and efficient. Furthermore, the accuracy and applicability of the k-? turbulence model are examined by comparing results of the computations with experimental data. The agreement is very good. 相似文献
2.
External heat transfer prediction is performed in two-dimensional turbine blade cascades using the Reynolds-averaged Navier–Stokes
equations. For this purpose, six different turbulence models including the algebraic Baldwin–Lomax (AIAA paper 78-257, 1978), three low-Re
k−ɛ models (Chien in AIAA J 20:33–38, 1982; Launder and Sharma in Lett Heat Mass Transf 1(2):131–138, 1974; Biswas and Fukuyama in J Turbomach 116:765–773, 1994), and two k−ω models (Wilcox in AIAA J 32(2):247–255, 1994) are taken into account. The computer code developed employs a finite volume method to solve governing equations based on
an explicit time marching approach with capability to simulate subsonic, transonic and supersonic flows. The Roe method is
used to decompose the inviscid fluxes and the gradient theorem to decompose viscous fluxes. The performance of different turbulence
models in prediction of heat transfer is examined. To do so, the effect of Reynolds and Mach numbers along with the turbulent
intensity are taken into account, and the numerical results obtained are compared with the experimental data available. 相似文献
3.
A. Marshall P. Venkateswaran D. Noble J. Seitzman T. Lieuwen 《Experiments in fluids》2011,51(3):611-620
Experimental turbulent combustion studies require systems that can simulate the turbulence intensities [u′/U
0 ~ 20–30% (Koutmos and McGuirk in Exp Fluids 7(5):344–354, 1989)] and operating conditions of real systems. Furthermore, it is important to have systems where turbulence intensity can be
varied independently of mean flow velocity, as quantities such as turbulent flame speed and turbulent flame brush thickness
exhibit complex and not yet fully understood dependencies upon both U
0 and u′. Finally, high pressure operation in a highly pre-heated environment requires systems that can be sealed, withstand high
gas temperatures, and have remotely variable turbulence intensity that does not require system shut down and disassembly.
This paper describes the development and characterization of a variable turbulence generation system for turbulent combustion
studies. The system is capable of a wide range of turbulence intensities (10–30%) and turbulent Reynolds numbers (140–2,200)
over a range of flow velocities. An important aspect of this system is the ability to vary the turbulence intensity remotely,
without changing the mean flow velocity. This system is similar to the turbulence generators described by Videto and Santavicca
(Combust Sci Technol 76(1):159–164, 1991) and Coppola and Gomez (Exp Therm Fluid Sci 33(7):1037–1048, 2009), where variable blockage ratio slots are located upstream of a contoured nozzle. Vortical structures from the slots impinge
on the walls of the contoured nozzle to produce fine-scale turbulence. The flow field was characterized for two nozzle diameters
using three-component Laser Doppler velocimetry (LDV) and hotwire anemometry for mean flow velocities from 4 to 50 m/s. This
paper describes the key design features of the system, as well as the variation of mean and RMS velocity, integral length
scales, and spectra with nozzle diameter, flow velocity, and turbulence generator blockage ratio. 相似文献
4.
Venkata Bharathi L. Boppana Zheng-Tong Xie Ian P. Castro 《Flow, Turbulence and Combustion》2012,88(3):311-342
Large-eddy simulations of the dispersion from scalar line sources at various locations within a fully developed turbulent
channel flow at Re = uh/ν = 10,400 are presented. Both mean and fluctuating scalar quantities are compared with those from the single available set
of experimental data (Lavertu and Mydlarski, J Fluid Mech 528:135–172, 2005) and differences are highlighted and discussed. The results are also discussed in the context of scalar dispersion in other
kinds of turbulent flows, e.g. homogeneous shear-flow. Initial computations at a much lower Reynolds number are also reported
and compared with the two available direct numerical simulation data sets. 相似文献
5.
Nonlocal generalizations of Burgers’ equation were derived in earlier work by Hunter (Contemp Math, vol 100, pp 185–202. AMS, 1989), and more recently by Benzoni-Gavage and Rosini (Comput Math Appl 57(3–4):1463–1484, 2009), as weakly nonlinear amplitude equations for hyperbolic boundary value problems admitting linear surface waves. The local-in-time well-posedness of such equations in Sobolev spaces was proved by Benzoni-Gavage (Differ Integr Equ 22(3–4):303–320, 2009) under an appropriate stability condition originally pointed out by Hunter. The same stability condition has also been shown to be necessary for well-posedness in Sobolev spaces in a previous work of the authors in collaboration with Tzvetkov (Benzoni-Gavage et al. in Adv Math 227(6):2220–2240, 2011). In this article, we show how the verification of Hunter’s stability condition follows from natural stability assumptions on the original hyperbolic boundary value problem, thus avoiding lengthy computations in each particular situation. We also show that the resulting amplitude equation has a Hamiltonian structure when the original boundary value problem has a variational origin. Our analysis encompasses previous equations derived for nonlinear Rayleigh waves in elasticity. 相似文献
6.
A thre-dimensional direct numerical simulation is combined with a laboratory study to describe the turbulent flow in an enclosed
annular rotor-stator cavity characterized by a large aspect ratio G = (b − a)/h = 18.32 and a small radius ratio a/b = 0.152, where a and b are the inner and outer radii of the rotating disk and h is the interdisk spacing. The rotation rate Ω considered is equivalent to the rotational Reynolds number Re = Ωb
2/ν= 9 .5 × 104 (ν the kinematic viscosity of water). This corresponds to a value at which experiment has revealed that the stator boundary
layer is turbulent, whereas the rotor boundary layer is still laminar. Comparisons of the computed solution with velocity
measurements have given good agreement for the mean and turbulent fields. The results enhance evidence of weak turbulence
by comparing the turbulence properties with available data in the literature (Lygren and Andersson, J Fluid Mech 426:297–326,
2001). An approximately self-similar boundary layer behavior is observed along the stator. The wall-normal variations of the structural
parameter and of characteristic angles confirm that this boundary layer is three-dimensional. A quadrant analysis (Kang et
al., Phys Fluids 10:2315–2322, 1998) of conditionally averaged velocities shows that the asymmetries obtained are dominated by Reynolds stress-producing events
in the stator boundary layer. Moreover, Case 1 vortices (with a positive wall induced velocity) are found to be the major
source of generation of special strong events, in agreement with the conclusions of Lygren and Andersson (J Fluid Mech 426:297–326,
2001). 相似文献
7.
V’yacheslav Akkerman Mikhail Ivanov Vitaly Bychkov 《Flow, Turbulence and Combustion》2009,82(3):317-337
Turbulence produced by the piston motion in spark-ignition engines is studied by 2D axisymmetric numerical simulations in
the cylindrical geometry as in the theoretical and experimental work by Breuer et al. (Flow Turbul Combust 74:145, 2005). The simulations are based on the Navier–Stokes gas-dynamic equations including viscosity, thermal conduction and non-slip
at the walls. Piston motion is taken into account as a boundary condition. The turbulent flow is investigated for a wide range
of the engine speed, 1,000–4,000 rpm, assuming both zero and non-zero initial turbulence. The turbulent rms-velocity and the
integral length scale are investigated in axial and radial directions. The rms-turbulent velocity is typically an order-of-magnitude
smaller than the piston speed. In the case of zero initial turbulence, the flow at the top-dead-center may be described as
a combination of two large-scale vortex rings of a size determined by the engine geometry. When initial turbulence is strong,
then the integral turbulent length demonstrates self-similar properties in a large range of crank angles. The results obtained
agree with the experimental observations of Breuer et al. (Flow Turbul Combust 74:145, 2005). 相似文献
8.
O. V. Kaptsov I. A. Efremov A. V. Shmidt 《Journal of Applied Mechanics and Technical Physics》2008,49(2):217-221
A second-order semi-empirical two-dimensional model of turbulence in the approximation of the far turbulent wake is considered.
The sought quantities are the velocity defect, kinetic turbulent energy, energy dissipation, and Reynolds stress. The full
group of transformations admitted by this model is found. Self-similar solutions satisfying natural boundary conditions are
constructed. The solutions obtained agree with experimental data.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 2, pp. 74–78, March–April, 2008. 相似文献
9.
Hot-wire and oil-film interferometry measurements are taken for 3D rough wall boundary layers at very high Reynolds numbers
(61,000 < Re θ < 120,000) with low blockage ratios, 10 < δ/H < 135, and high roughness, 100 < H
+ < 4,900. The results cover flows over both rough walls and over obstacles and are compared with and provide extension to
recent lower Reynolds number results. The validity of the Townsend ‘wall similarity hypothesis’ in relation to consistently
increasing 3D roughness is interrogated. In agreement with recent work, Schultz and Flack (J Fluid Mech 580:381–405, 2007) and Castro (J Fluid Mech 585:469–485, 2007) found that, for relatively low roughness, Townsend’s hypothesis holds for the mean velocity field. With increasing roughness,
the equilibrium layer diminishes and gradually vanishes. The viscous component of the wall shear stress decreases, while the
turbulent component increases as the roughness effects extend across the boundary layer. 相似文献
10.
Marc Terracol 《Flow, Turbulence and Combustion》2006,77(1-4):161-184
Hybrid CFD/CAA methods have generally to be used for the numerical simulation of trailing-edge noise (see [9, 20] for instance). This study focuses on the first step of such hybrid methods, which is to predict the unsteady aerodynamic sources by the mean of a 3D unsteady simulation of the flow. Such a simulation is however generally still away from the numerical capabilities of ‘usual’ supercomputers. This paper investigates the use of a zonal LES method (based on the NLDE – Non-Linear Disturbance Equations – technique) for the numerical prediction of the aerodynamic noise sources. This method makes it possible to perform only zonal LES close to the main elements responsible of sound generation, while the overall configuration is only treated by a RANS approach. Attention will be paid to the specific boundary treatment at the interface between the RANS and LES regions. More precisely, the problem of the generation of turbulent inflow conditions for the LES region will be carefully addressed. The method is first assessed in the simulation of a flat plate ended by a blunted trailing-edge, and then applied to the simulation of the flow over a NACA0012 airfoil with blunted trailing-edge. 相似文献
11.
An experimental study was conducted to examine the effects of surface roughness and adverse pressure gradient (APG) on the
development of a turbulent boundary layer. Hot-wire anemometry measurements were carried out using single and X-wire probes in all regions of a developing APG flow in an open return wind tunnel test section. The same experimental conditions
(i.e., T
∞, U
ref, and C
p) were maintained for smooth, k
+ = 0, and rough, k
+ = 41–60, surfaces with Reynolds number based on momentum thickness, 3,000 < Re
θ < 40,000. The experiment was carefully designed such that the x-dependence in the flow field was known. Despite this fact, only a very small region of the boundary layer showed a balance
of the various terms in the integrated boundary layer equation. The skin friction computed from this technique showed up to
a 58% increase due to the surface roughness. Various equilibrium parameters were studied and the effect of roughness was investigated.
The generated flow was not in equilibrium according to the Clauser (J Aero Sci 21:91–108, 1954) definition due to its developing nature. After a development region, the flow reached the equilibrium condition as defined
by Castillo and George (2001), where Λ = const, is the pressure gradient parameter. Moreover, it was found that this equilibrium condition can be used
to classify developing APG flows. Furthermore, the Zagarola and Smits (J Fluid Mech 373:33–79, 1998a) scaling of the mean velocity deficit, U
∞δ*/δ, can also be used as a criteria to classify developing APG flows which supports the equilibrium condition of Castillo
and George (2001). With this information a ‘full APG region’ was defined. 相似文献
12.
Shuojun Li David Montgomery Wesley B. Jones 《Theoretical and Computational Fluid Dynamics》1997,9(3-4):167-181
We report numerical computations of decaying two-dimensional Navier--Stokes turbulence inside a circular rigid boundary.
We summarize previously reported calculations involving no-slip boundary conditions and present results with higher spatial
resolution than achieved before (with, however, no qualitative changes in the observed behavior). We then report new results
with stress-free boundary conditions (for a viscous fluid, but bounded by a perfectly slippery wall). The method used is spectral,
involving expansions of the fields in orthonormal sets of functions which obey two boundary conditions (circular analogues
of the Chandrasekhar–Reid functions). The computation takes place entirely in the spectral space. Large-scale Reynolds numbers
are typically less than a thousand. Interest focuses on the role played by angular momentum, in determining the decay of the
turbulence with no-slip boundary conditions, and the role of possible other ideal invariants in the stress-free case.
Received 30 September 1996 and accepted 5 February 1997 相似文献
13.
This paper is devoted to the computation of turbulent flows by a Galerkin finite element method. Effects of turbulence on the mean field are taken into account by means of a k-? turbulence model. The wall region is treated through wall laws and, more specifically, Reichardt's law. An inlet profile for ? is proposed as a numerical treatment for physically meaningless values of k and ?. Results obtained for a recirculating flow in a two-dimensional channel with a sudden expansion in width are presented and compared with experimental values. 相似文献
14.
The present paper is devoted to the computation of turbulent flows by a Galerkin finite element method. Effects of turbulence on the mean field are taken into account by means of a (k-ε) turbulence model. The wall region is treated through wall laws and, more specifically, Reichardt's law. An inlet profile for ε is proposed as a numerical treatment for physically meaningless values of k and ε. Results obtained for a recirculating flow in a two-dimensional channel with a sudden expansion in width are presented and compared with experimental values. 相似文献
15.
The turbulence structure near a wall is a very active subject of research and a key to the understanding and modeling of this
flow. Many researchers have worked on this subject since the fifties Hama et al. (J Appl Phys 28:388–394, 1957). One way to study this organization consists of computing the spatial two-point correlations. Stanislas et al. (C R Acad
Sci Paris 327(2b):55–61, 1999) and Kahler (Exp Fluids 36:114–130, 2004) showed that double spatial correlations can be computed from stereoscopic particle image velocimetry (SPIV) fields and can
lead to a better understanding of the turbulent flow organization. The limitation is that the correlation is only computed
in the PIV plane. The idea of the present paper is to propose a new method based on a specific stereoscopic PIV experiment
that allows the computation of the full 3D spatial correlation tensor. The results obtained are validated by comparison with
2D computation from SPIV. They are in very good agreement with the results of Ganapthisubramani et al. (J Fluid Mech 524:57–80,
2005a). 相似文献
16.
In this paper, a numerical investigation of laminar natural convection flows in a vertical channel with obstructions is carried
out. The main purpose was to analyze the effects of the locations of symmetric obstructions. The computations were performed
in a two-dimensional domain and a symmetric uniform wall temperature has been taken as thermal boundary condition. The governing
equations were solved using a control volume method and the SIMPLER algorithm for the velocity–pressure coupling was employed.
The profiles of the local Nusselt number were given for three different locations of the obstructions. The variation of the
average Nusselt number and inlet flow rate versus the modified Rayleigh number were investigated. The results demonstrated
that the average Nusselt number decreases as the distance of the obstructions from the inlet increases.
Received on 17 January 2000 相似文献
17.
We present a generalised treatment of the wall boundary conditions for RANS computation of turbulent flows and heat transfer.
The method blends the integration up to the wall (ItW) with the generalised wall functions (GWF) that include non-equilibrium effects. Wall boundary condition can thus be defined irrespective of whether the wall-nearest
grid point lies within the viscous sublayer, in the buffer zone, or in the fully turbulent region. The computations with fine
and coarse meshes of a steady and pulsating flow in a plane channel, in flow behind a backward-facing step and in a round
impinging jet using the proposed compound wall treatment (CWT) are all in satisfactory agreement with the available experiments and DNS data. The method is recommended for computations
of industrial flows in complex domains where it is difficult to generate a computational grid that will satisfy a priori either
the ItW or WF prerequisites. 相似文献
18.
Incompressible 3-D DNS is performed in non-decaying turbulence with single step chemistry to validate a new analytical expression
for turbulent burning velocity. The proposed expression is given as a sum of laminar and turbulent contributions, the latter
of which is given as a product of turbulent diffusivity in unburned gas and inverse scale of wrinkling at the leading edge.
The bending behavior of U
T at higher u′ was successfully reproduced by the proposed expression. It is due to decrease in the inverse scale of wrinkling at the leading
edge, which is related with an asymmetric profile of FSD with increasing u′. Good agreement is achieved between the analytical expression and the turbulent burning velocities from DNS throughout the
wrinkled, corrugated and thin reaction zone regimes. Results show consistent behavior with most experimental correlations
in literature including those by Bradley et al. (Philos Trans R Soc Lond A 338:359–387, 1992), Peters (J Fluid Mech 384:107–132, 1999) and Lipatnikov et al. (Progr Energ Combust Sci 28:1–74, 2002). 相似文献
19.
Babanin and Haus (J Phys Oceanogr 39:2675–2679, 2009) recently presented evidence of near-surface turbulence generated below steep non-breaking deep-water waves. They proposed
a threshold wave parameter a
2ω/ν = 3,000 for the spontaneous occurrence of turbulence beneath surface waves. This is in contrast to conventional understanding
that irrotational wave theories provide a good approximation of non-wind-forced wave behaviour as validated by classical experiments.
Many laboratory wave experiments were carried out in the early 1960s (e.g. Wiegel 1964). In those experiments, no evidence of turbulence was reported, and steep waves behaved as predicted by the high-order irrotational
wave theories within the accuracy of the theories and experimental techniques at the time. This contribution describes flow
visualisation experiments for steep non-breaking waves using conventional dye techniques in the wave boundary layer extending
above the wave trough level. The measurements showed no evidence of turbulent mixing up to a value of a
2ω/ν = 7,000 at which breaking commenced in these experiments. These present findings are in accord with the conventional understandings
of wave behaviour. 相似文献
20.
Steady turbulent viscous incompressible fluid flow in a plane channel is calculated for the case of uniform blowing and suction
through opposite walls. There are no experimental data for flows of this type. The flows were calculated by two methods: a
direct numerical simulation method and using a three-parameter turbulence model. Direct numerical simulation was carried out
using the same (apart from the boundary conditions) algorithm for numerical solution of the Navier-Stokes equations as that
used earlier for calculating flows in pipes and channels with impermeable walls. In the second group of calculations the version
of the model published in 1978 was used. The results obtained by the two methods are in good agreement. The difference is
within the spread of the experimental data used for determining the parameters of the model. The agreement obtained makes
it possible to assert that the turbulence direct numerical simulation algorithm developed can be used for the analysis of
flows with quite different boundary conditions, including cases where there are no corresponding experimental data.
Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 6, pp. 18–26, November–December,
1998.
The work was financially supported by the Russian Foundation for Basic Research (project Nos. 96-01-00602 and 96-01-00259). 相似文献