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1.
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
2.
Ratnesh K. Shukla Jeff. D. Eldredge 《Theoretical and Computational Fluid Dynamics》2007,21(5):343-368
An inviscid vortex sheet model is developed in order to study the unsteady separated flow past a two-dimensional deforming
body which moves with a prescribed motion in an otherwise quiescent fluid. Following Jones (J Fluid Mech 496, 405–441, 2003)
the flow is assumed to comprise of a bound vortex sheet attached to the body and two separate vortex sheets originating at
the edges. The complex conjugate velocity potential is expressed explicitly in terms of the bound vortex sheet strength and
the edge circulations through a boundary integral representation. It is shown that Kelvin’s circulation theorem, along with
the conditions of continuity of the normal velocity across the body and the boundedness of the velocity field, yields a coupled
system of equations for the unknown bound vortex sheet strength and the edge circulations. A general numerical treatment is
developed for the singular principal value integrals arising in the solution procedure. The model is validated against the
results of Jones (J Fluid Mech 496, 405–441, 2003) for computations involving a rigid flat plate and is subsequently applied
to the flapping foil experiments of Heathcote et al. (AIAA J, 42, 2196–2204, 2004) in order to predict the thrust coefficient.
The utility of the model in simulating aquatic locomotion is also demonstrated, with vortex shedding suppressed at the leading
edge of the swimming body.
相似文献
3.
A hyperbolic multiphase flow model with a single pressure and a single velocity but several temperatures is proposed to deal
with the detonation dynamics of condensed energetic materials. Temperature non-equilibrium effects are mandatory in order
to deal with wave propagation (shocks, detonations) in heterogeneous mixtures. The model is obtained as the asymptotic limit
of a total non-equilibrium multiphase flow model in the limit of stiff mechanical relaxation only (Kapila et al. in Phys Fluids
13:3002–3024, 2001). Special attention is given to mass transfer modelling, that is obtained on the basis of entropy production
analysis in each phase and in the system (Saurel et al. in J Fluid Mech 607:313–350, 2008). With the help of the shock relations
given in Saurel et al. (Shock Waves 16:209–232, 2007) the model is closed and provides a generalized ZND formulation for condensed
energetic materials. In particular, generalized CJ conditions are obtained. They are based on a balance between the chemical
reaction energy release and internal heat exchanges among phases. Moreover, the sound speed that appears at sonic surface
corresponds to the one of Wood (A textbook of sound, G. Bell and Sons LTD, London, 1930) that presents a non-monotonic behaviour
versus volume fraction. Therefore, non-conventional reaction zone structure is observed. When heat exchanges are absent, the
conventional ZND model with conventional CJ conditions is recovered. When heat exchanges are involved interesting features
are observed. The flow behaviour presents similarities with non ideal detonations (Wood and Kirkwood in J Chem Phys 22:1920–1924,
1950) and pathological detonations (Von Neuman in Theory of detonation waves, 1942; Guenoche et al. in AIAA Prog Astron Aeronaut
75: 387–407, 1981). It also present non-conventional behaviour with detonation velocity eventually greater than the CJ one.
Multidimensional resolution of the corresponding model is then addressed. This poses serious difficulties related to the presence
of material interfaces and shock propagation in multiphase mixtures. The first issue is solved by an extension of the method
derived in Saurel et al. (J Comput Phys 228(5):1678–1712, 2009) in the presence of heat and mass transfers. The second issue
poses the difficult mathematical question of numerical approximation of non-conservative systems in the presence of shocks
associated to the physical question of energy partition among phases for a multiphase shock. A novel approach is used, based
on extra evolution equations used to retain the information of the material initial state. This method insures convergence
in the post-shock state. Thanks to these various theoretical and numerical ingredients, one-dimensional and multidimensional
unsteady detonation waves computations are done, eventually in the presence of material interfaces. Convergence of the numerical
hyperbolic solver against ZND multiphase solution is reached. Material interfaces, shocks, detonations are solved with a unified
formulation where the same equations are solved everywhere with the same numerical scheme. 相似文献
4.
Noise Investigation of a High Subsonic, Moderate Reynolds Number Jet Using a Compressible Large Eddy Simulation 总被引:1,自引:0,他引:1
This study investigates the noise radiated by a subsonic circular jet with a Mach number of 0.9 and a Reynolds number of 65000
computed by a compressible Large Eddy Simulation (LES). First, it demonstrates the feasibility of using LES to predict accurately
both the flow field and the sound radiation on a domain including the acoustic field. Mean flow parameters, turbulence intensities,
velocity spectra and integral length scales are in very good agreement with experimental data. The noise generated by the
jet, provided directly by the simulation, is also consistent with measurements in terms of sound pressure spectra, levels
and directivity. The apparent location of the sound sources is at the end of the potential core in accordance with some experimental
observations at similar Reynolds numbers and Mach numbers. Second, the noise generation mechanisms are discussed in an attempt
to connect the flow field with the acoustic field. This study shows that for the simulated moderate Reynolds number jet, the
predominant sound radiation in the downstream direction is associated with the breakdown of the shear layers in the central
jet zone.
Received 24 January 2002 and accepted 16 July 2002 Published online 3 December 2002
RID="*"
ID="*" A preliminary version of some of the results presented here was reported in AIAA Paper 2000–2009 presented at the 6th
AIAA/CEAS Aeroacoustics Conference in Lahaina, Hawaii, June 2000. Computing time was supplied by the Institut du Développement
et des Ressources en Informatique Scientifique (IDRIS – CNRS).
Communicated by T.B. Gatski 相似文献
5.
François Golanski Véronique Fortuné Eric Lamballais 《Theoretical and Computational Fluid Dynamics》2005,19(6):391-416
The ability of Lighthill's analogy to predict the sound radiated by a transitional mixing layer is evaluated by means of direct
numerical simulation (DNS). The specific case of low Mach number flows with density variations is investigated. In order to
limit the global computational cost, the acoustic source information is based on numerical results where the sound waves have
been removed. It is shown that the low Mach number approximation coupled with the acoustic analogy can lead to very accurate
predictions for the radiated sound if the acoustic sources in Lighthill's equation are taken into account carefully. Results
for the acoustic intensity deduced from a repeated use of the Lighthill's analogy over a wide range of Mach numbers allow
us to discuss the adequacy of scaling laws proposed by previous authors (J. Sound Vib. 28(3), 563–585, 1973; 31(4), 391–397, 1973; 48(1), 95–111, 1976) for the prediction of noise from hot jets. 相似文献
6.
Ahmed A. Afify 《Transport in Porous Media》2007,66(3):391-401
An analysis is presented to investigate the effects of temperature-dependent viscosity, thermal dispersion, Soret number and
Dufour number on non-Darcy MHD free convective heat and mass transfer of a viscous, incompressible and electrically conducting
fluid past a vertical isothermal surface embedded in a saturated porous medium. The governing partial differential equations
are transferred into a system of ordinary differential equations, which are solved numerically using a fourth order Runge–Kutta
scheme with the shooting method. Comparisons with previously published work by Hong and Tien [Hong, J. T. and Tien, C. L.:
1987, Int. J. Heat Mass Transfer
30, 143–150] and Sparrow et al. [Sparrow, E. M. et al.: 1964, AIAA J. 2 652–659] are performed and good agreement is obtained. Numerical results of the skin friction coefficient, the local Nusselt
number and the local Sherwood number as well as the velocity, temperature and concentration profiles are presented for different
physical parameters. 相似文献
7.
8.
9.
Jens Rottmann-Matthes 《Journal of Dynamics and Differential Equations》2012,24(2):341-367
It is a well-known problem to derive nonlinear stability of a traveling wave from the spectral stability of a linearization.
In this paper we prove such a result for a large class of hyperbolic systems. To cope with the unknown asymptotic phase, the
problem is reformulated as a partial differential algebraic equation for which asymptotic stability becomes usual Lyapunov
stability. The stability proof is then based on linear estimates from (Rottmann-Matthes, J Dyn Diff Equat 23:365–393, 2011) and a careful analysis of the nonlinear terms. Moreover, we show that the freezing method (Beyn and Thümmler, SIAM J Appl
Dyn Syst 3:85–116, 2004; Rowley et al. Nonlinearity 16:1257–1275, 2003) is well-suited for the long time simulation and numerical approximation of the asymptotic behavior. The theory is illustrated
by numerical examples, including a hyperbolic version of the Hodgkin–Huxley equations. 相似文献
10.
The purpose of this study is to implement a new analytical method which is a combination of the homotopy analysis method (HAM)
and the Padé approximant for solving magnetohydrodynamic boundary-layer flow. The solution is compared with the numerical
solution. Comparisons between the HAM–Padé and the numerical solution reveal that the new technique is a promising tool for
solving MHD boundary-layer equations. The effects of the various parameters on the velocity and temperature profiles are presented
graphically form. Favorable comparisons with previously published works (Crane, J. Appl. Math. Phys. 21:645–647, 1970, and Vajravelu and Hadjinicolaou, Int. J. Eng. Sci. 35:1237–1244, 1997) are obtained. It is predicted that HAM–Padé can have wide application in engineering problems (especially for boundary-layer
and natural convection problems). 相似文献
11.
Matteo Negri 《Journal of Elasticity》2010,98(2):159-187
On the base of many experimental results, e.g., Ravi-Chandar and Knauss (Int. J. Fract. 26:65–80, 1984), Sharon et al. (Phys. Rev. Lett. 76(12):2117–2120, 1996), Hauch and Marder (Int. J. Fract. 90:133–151, 1998), the object of our analysis is a rate-dependent model for the propagation of a crack in brittle materials. Restricting ourselves
to the quasi-static framework, our goal is a mathematical study of the evolution equation in the geometries of the ‘Single
Edge Notch Tension’ and of the ‘Compact Tension’. Besides existence and uniqueness, emphasis is placed on the regularity of
the evolution making reference also to the ‘velocity gap’. The transition to the rate-independent model of Griffith is obtained
by time rescaling, proving convergence of the rescaled evolutions and of their energies. Further, the discontinuities of the
rate-independent evolution are characterized in terms of unstable points of the free energy. Results are illustrated by a
couple of numerical examples in the above mentioned geometries. 相似文献
12.
In this work, the authors study the influence of noise on the dynamics of base-excited elastic cantilever structures at the
macroscale and microscale by using experimental, numerical, and analytical means. The macroscale system is a base excited
cantilever structure whose tip experiences nonlinear interaction forces. These interaction forces are constructed to be similar
in form to tip interaction forces in tapping mode atomic force microscopy (AFM). The macroscale system is used to study nonlinear
phenomena and apply the associated findings to the chosen AFM application. In the macroscale experiments, the tip of the cantilever
structure experiences long-range attractive and short-range repulsive forces. There is a small magnet attached to the tip,
and this magnet is attracted by another one mounted to a high-resolution translatory stage. The magnet fixed to the stage
is covered by a compliant material that is periodically impacted by the cantilever’s tip. Building on their earlier work,
wherein the authors showed that period-doubling bifurcations associated with near-grazing impacts occur during off-resonance
base excitations of macroscale and microscale cantilevers, in the present work, the authors focus on studying the influence
of Gaussian white noise when it is included as an addition to a deterministic base excitation input. The repulsive forces
are modeled as Derjaguin–Muller–Toporov (DMT) contact forces in both the macroscale and microscale systems, and the attractive
forces are modeled as van der Waals attractive forces in the microscale system and magnetic attractive forces in the macroscale
system. A reduced-order model, based on a single mode approximation is used to numerically study the response for a combined
deterministic and random base excitation. It is experimentally and numerically found that the addition of white Gaussian noise
to a harmonic base excitation facilitates contact between the tip and the sample, when there was previously no contact with
only the harmonic input, and results in a response that is nominally close to a period-doubled orbit. The qualitative change
observed with the addition of noise is associated with near-grazing impacts between the tip and the sample. The numerical
and experimental results further motivate the formulation of a general analytical framework, in which the Fokker–Planck equation
is derived for the cantilever-impactor system. After making a set of approximations, the moment evolution equations are derived
from the Fokker–Planck equation and numerically solved. The resulting findings support the experimental results and demonstrate
that noise can be added to the input to facilitate contact between the cantilever’s tip and the surface, when there was previously
no contact with only a harmonic input. The effects of Gaussian white noise are numerically studied for a tapping mode AFM
application, and it is shown that contact between the tip and the sample can be realized by adding noise of an appropriate
level to a harmonic excitation. 相似文献
13.
B. Straughan 《Transport in Porous Media》2009,77(2):159-168
We revisit the problem of thermal convection in a bidispersive porous medium, first addressed by Nield and Kuznetsov (Int.
J. Heat Mass Transfer, 49: 3068–3074, 2006). We investigate the possibility of oscillatory convection by using a highly accurate
Chebyshev tau
numerical method. We also develop a nonlinear energy stability theory for the same problem. This yields a global stability
threshold below which instabilities cannot arise. These thresholds together with the linear instability boundaries yield a
zone where thermal instability may be found. The results and theory of Nield and Kuznetsov (Int. J. Heat Mass Transfer, 49:
3068–3074, 2006) are thus proven to be a highly important development in the modern theory of designer porous materials, cf.
Nield and Bejan (Convection in Porous Media, Springer, New York, 2006), pp. 94–97.
This work was supported in part by a Research Project Grant of the Leverhulme Trust—Grant Number F/00128/AK. 相似文献
14.
Analytical expressions for the scaling factor (A) in the Wooding and Chapman (J Geophys Res 71:2895–2902, 1966) solution for steady-state flow to drains on a sloping bed
are presented. Otherwise A needs to be obtained by matching numerical and solutions. Corrections to various errors in other analytical solutions are
given. The HYDRUS2D numerical model was used to generate results for steady-state flow to drains on a sloping bed which were
compared to published Hele-Shaw cell results. The numerical results were used to compute both the pressure head on the bottom
and the height of the phreatic surface. The numerical results for maximum water-table height are almost exactly the same as
the published Hele-Shaw cell results and are greater than the numerical values for the maximum pressure heads on the sloping
base. These HYDRUS2D model results were then compared with various analytical solutions, and it was found that Towner’s (Water
Resour Res 11:144–147, 1975) solution gave the best results for both estimation of the maximum height of the phreatic surface
and the position on the slope where this occurs. 相似文献
15.
A brief review of recent progress in the field of computational aeroacoustics (CAA) is proposed. This paper is complementary to the previous reviews of Tam [(1995a) “Computational aeroacoustics: issues and methods”, AIAA J. 33(10), 1788–1796], Lele [(1997) “Computational Aeroacoustics: a review”, AIAA Paper 97–0018, 35th Aerospace Sciences Meeting and Exhibit, Reno, Nevada] and Glegg [(1999) “Recent advances aeroacoustics: the influence of computational fluid dynamics”, 6th International Congress on Sound and Vibration, Copenhagen, Danemark, 5–8 July, 43–58] on advances in CAA. After a short introduction concerning the current motivations of jet noise studies, connections between computational fluid dynamics (CFD) and CAA using hybrid approaches are discussed in the first part. The most spectacular advances are probably provided by the direct computation of jet noise, and some recent results are shown in the second part. 相似文献
16.
The injection of CO2 in exploited natural gas reservoirs as a means to reduce greenhouse gas (GHG) emissions is highly attractive as it takes
place in well-known geological structures of proven integrity with respect to gas leakage. The injection of a reactive gas
such as CO2 puts emphasis on the possible alteration of reservoir and caprock formations and especially of the wells’ cement sheaths
induced by the modification of chemical equilibria. Such studies are important for injectivity assurance, wellbore integrity,
and risk assessment required for CO2 sequestration site qualification. Within a R&D project funded by Eni, we set up a numerical model to investigate the rock–cement
alterations driven by the injection of CO2 into a depleted sweet natural gas pool. The simulations are performed with the TOUGHREACT simulator (Xu et al. in Comput
Geosci 32:145–165, 2006) coupled to the TMGAS EOS module (Battistelli and Marcolini in Int J Greenh Gas Control 3:481–493, 2009) developed for the TOUGH2 family of reservoir simulators (Pruess et al. in TOUGH2 User’s Guide, Version 2.0, 1999). On the basis of field data, the system is considered in isothermal (50°C) and isobaric (128.5 bar) conditions. The effects of the evolving reservoir gas composition are taken into account before,
during, and after CO2 injection. Fully water-saturated conditions were assumed for the cement sheath and caprock domains. The gas phase does not
flow by advection from the reservoir into the interacting domains so that molecular diffusion in the aqueous phase is the
most important process controlling the mass transport occurring in the system under study. 相似文献
17.
In this study, we use the method of homogenization to develop a filtration law in porous media that includes the effects of
inertia at finite Reynolds numbers. The result is much different than the empirically observed quadratic Forchheimer equation.
First, the correction to Darcy’s law is initially cubic (not quadratic) for isotropic media. This is consistent with several
other authors (Mei and Auriault, J Fluid Mech 222:647–663, 1991; Wodié and Levy, CR Acad Sci Paris t.312:157–161, 1991; Couland
et al. J Fluid Mech 190:393–407, 1988; Rojas and Koplik, Phys Rev 58:4776–4782, 1988) who have solved the Navier–Stokes equations
analytically and numerically. Second, the resulting filtration model is an infinite series polynomial in velocity, instead
of a single corrective term to Darcy’s law. Although the model is only valid up to the local Reynolds number, at the most,
of order 1, the findings are important from a fundamental perspective because it shows that the often-used quadratic Forchheimer
equation is not a universal law for laminar flow, but rather an empirical one that is useful in a limited range of velocities.
Moreover, as stated by Mei and Auriault (J Fluid Mech 222:647–663, 1991) and Barree and Conway (SPE Annual technical conference
and exhibition, 2004), even if the quadratic model were valid at moderate Reynolds numbers in the laminar flow regime, then
the permeability extrapolated on a Forchheimer plot would not be the intrinsic Darcy permeability. A major contribution of
this study is that the coefficients of the polynomial law can be derived a priori, by solving sequential Stokes problems.
In each case, the solution to the Stokes problem is used to calculate a coefficient in the polynomial, and the velocity field
is an input of the forcing function, F, to subsequent problems. While numerical solutions must be utilized to compute each coefficient in the polynomial, these
problems are much simpler and robust than solving the full Navier–Stokes equations. 相似文献
18.
The velocity field and skin friction distribution around a row of five jets issuing into a crossflow from short (L/D ≃ 1) pipes inclined by 35° with respect to the streamwise direction, (i.e., “short holes”) are presented for two different
jet supply flow directions. Velocity was measured using PIV, while the skin friction was measured with oil-film interferometry.
The flow features are compared with previously published data for jets issuing through holes oriented normal to the crossflow
and with numerical simulations of similar geometries. The distinguishing features of the flow field include a reduced recirculation
region in comparison to the 90° case and markedly different in-hole flow physics. The jetting process caused by in-hole separations
force the bulk of the jet fluid to issue from the leading half of the streamwise-angled injection hole, as previously reported
by Brundage et al. (Tech Rep ASME 99-GT-35, 1999) and predicted by Walters and Leylek (ASME J Turbomach 122:101–112, 2000). The flow structure impacts the skin friction distribution around the holes, resulting in higher near-hole shear stress
for a counter-flow supply plenum (jet fluid supplied by a high speed plenum flowing opposite to the free stream direction).
In contrast, the counter-flow supply plenum was previously found to have the lowest near-hole wall shear stress for normal
injection holes (Peterson and Plesniak in Exp Fluids 37:497–503, 2004b). Streamwise-angled injection generally reduces the near-hole skin friction due to the reduced jet trajectory resulting from
the lower wall-normal jet momentum. Far downstream, the skin friction distributions are similar for the two injection angle
cases. 相似文献
19.
Katja Lappalainen Mikko Manninen Ville Alopaeus Juhani Aittamaa John Dodds 《Transport in Porous Media》2009,77(1):17-40
Capillary pressure is considered in packed-beds of spherical particles. In the case of gas–liquid flows in packed-bed reactors,
capillary pressure gradients can have a significant influence on liquid distribution and, consequently, on the overall reactor
performance. In particular, capillary pressure is important for non-uniform liquid distribution, causing liquid spreading
as it flows down the packing. An analytical model for capillary pressure–saturation relation is developed for the pendular
and funicular regions and the factors affecting capillary pressure in the capillary region are discussed. The present model
is compared to the capillary pressure models of Grosser et al. (AIChE J., 34:1850–1860, 1988) and Attou and Ferschneider (Chem.
Eng. Sci., 55:491–511, 2000) and to the experiments of Dodds and Srivastava (Part Part Syst. Charact., 23:29–39, 2006) and
Dullien et al. (J. Colloid Interface Sci., 127:362–372, 1989). The non-homogeneity of real packings is considered through
particle size and porosity distributions. The model is based on the assumption that the particles are covered with a liquid
film, which provides hydrodynamic continuity. This makes the model more suitable for porous or rough particles than for non-porous
smooth particles. The main improvements of the present model are found in the pendular region, where the liquid dispersion
due to capillary pressure gradients is most significant. The model can be used to improve the hydrodynamic models (e.g., CFD
and cellular automata models) for packed-bed reactors, such as trickle-bed reactors, where gas, liquid, and solid phases are
present. Models for such reactors have become quite common lately (Sáez and Carbonell, AIChE J., 31:52–62, 1985; Holub et al.,
Chem. Eng. Sci, 47, 2343–2348, 1992; Attou et al., Chem. Eng. Sci., 54:785–802, 1999; Iliuta and Larachi, Chem. Eng. Sci.,
54:5039–5045, 1999, IJCRE 3:R4, 2005; Narasimhan et al., AIChE J., 48:2459–2474, 2002), but they still lack proper terms causing
liquid dispersion. 相似文献
20.
This paper reports on the simulation of the near-nozzle region of an isothermal Mach 0.6 jet at a Reynolds number of 100,000
exhausting from a round nozzle geometry. The flow inside the nozzle and the free jet outside the nozzle are computed simultaneously
by a high-order accurate, multi-block, large eddy simulation (LES) code with overset grid capability. The total number of
grid points at which the governing equations are solved is about 50 million. The main emphasis of the simulation is to capture
the high frequency noise generation that takes place in the shear layers of the jet within the first few diameters downstream
of the nozzle exit. Although we have attempted to generate fully turbulent boundary layers inside the nozzle by means of a
special turbulent inflow generation procedure, an analysis of the simulation results supports the fact that the state of the
nozzle exit boundary layer should be characterized as transitional rather than fully turbulent. This is believed to be most
likely due to imperfections in the inflow generation method. Details of the computational methodology are presented together
with an analysis of the simulation results. A comparison of the far field noise spectrum in the sideline direction with experimental
data at similar flow conditions is also carried out. Additional noise generation due to vortex pairing in the region immediately
downstream of the nozzle exit is also observed. In a second simulation, the effect of the nozzle exit boundary layer thickness
on the vortex pairing Strouhal frequency (based on nozzle diameter) and its harmonics is demonstrated. The limitations and
deficiencies of the present study are identified and discussed. We hope that the lessons learned in this study will help guide
future research activities towards resolving the pending issues identified in this work.
Presented as AIAA Paper 2006-2499 at 12th AIAA/CEAS Aeroacoustics Conference, 8–10 May 2006, Cambridge, MA, USA. 相似文献
Presented as AIAA Paper 2006-2499 at 12th AIAA/CEAS Aeroacoustics Conference, 8–10 May 2006, Cambridge, MA, USA. 相似文献