Mean statistics of a heated turbulent pipe flow at supercritical pressure

Nemati, Hassan; Patel, Ashish; Boersma, Bendiks Jan; Pečnik, René

doi:10.1016/j.ijheatmasstransfer.2014.12.039

Cited by 93 publications

(56 citation statements)

References 30 publications

(42 reference statements)

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“…Using the lowMach-number approximation, density and other transport properties can be evaluated independently of pressure fluctuations as a function of temperature only [7,25]. The flow is driven by a constant streamwise pressure gradient.…”

Section: Simulation Detailsmentioning

confidence: 99%

“…Some of the well-known examples which involve variable thermophysical properties include supersonic flows for aircraft and propulsion systems, strongly heated or cooled flows in heat exchangers, or chemically reacting flows in combustion chambers. Furthermore, recently, in order to increase the efficiency of power cycles, there is increased interest in studying turbulent heat transfer to fluids at supercritical pressure [6][7][8]. These fluids exhibit strong thermophysical property variations due to a strong dependence of properties on temperature.…”

Section: Introductionmentioning

confidence: 99%

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Scalar statistics in variable property turbulent channel flows

2017

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Direct numerical simulation of fully developed, internally heated channel flows with isothermal walls is performed using the low-Mach-number approximation of Navier-Stokes equation to investigate the influence of temperature-dependent properties on turbulent scalar statistics. Different constitutive relations for density ρ, viscosity μ, and thermal conductivity λ as a function of temperature are prescribed in order to characterize the turbulent scalar statistics. It is shown that the dominant effect caused by property variations on scalar statistics can be parameterized by two nondimensional parameters, namely the semilocal Reynolds number Re τ ≡ Re τ √ (ρ/ρ w )/(μ/μ w ) (the bar and subscript w denote Reynolds averaging and wall value respectively, while Re τ is the friction Reynolds number based on wall values), and the local Prandtl number Pr = Pr w (μ/μ w )/(λ/λ w ) (Pr w is the molecular Prandtl number based on wall values). Near-wall gradients in Re τ modulate the turbulent heat flux generation mechanism because of structural changes in turbulence. However, the influence of these modulations on the inner scaling of turbulent heat conductivity normalized by local mean viscosity is shown to be weak. Using this observation, a temperature transformation is derived that is invariant of Re τ variations and only exhibits a Pr -dependent shift.

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Section: Simulation Detailsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Scalar statistics in variable property turbulent channel flows

2017

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“…In the low Mach number limit, acoustic wave propagation is ignored and the pressure field is decomposed into a thermodynamic P 0 (t) and a hydrodynamic component p(x i ,t). 22,23 Furthermore, for a calorifically perfect fluid in a closed system with zero net heat flux, it can be shown that P 0 is independent of time. 24 The density and transport properties can then be evaluated independently of the hydrodynamic pressure variations (p ≪ P 0 ) as a function of temperature alone.…”

Section: A Governing Equations and Computational Approachmentioning

confidence: 99%

“…Such a behaviour can qualitatively occur in fluids at supercritical pressures close to the pseudo-critical point; both ρ and µ decrease with increase of temperature. 23 GL corresponds to a gas-like property variation, whereby ρ decreases and µ increases with increase of T. LL corresponds to a liquid-like behaviour as µ deceases with increase of T. Cν refers to a constant kinematic viscosity ν case with ρ(T) = µ(T). Finally, SRe * τCν and SRe * τGL are hypothetical cases that resemble similar Re * τ profiles as cases Cν and GL, respectively, but with different functional relations for ρ and µ.…”

Section: Numerical Experimentsmentioning

confidence: 99%

Semi-local scaling and turbulence modulation in variable property turbulent channel flows

et al. 2015

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We theoretically and numerically investigate the effect of temperature dependent density and viscosity on turbulence in channel flows. First, a mathematical framework is developed to support the validity of the semi-local scaling as proposed based on heuristic arguments by Huang, Coleman, and Bradshaw ["Compressible turbulent channel flows: DNS results and modelling," J. Fluid Mech. 305, 185-218 (1995)]. Second, direct numerical simulations (DNS) of turbulent channel flows with different constitutive relations for density and viscosity are performed to assess and validate the semi-local scaling for turbulent statistics. The DNS database is obtained by solving the low-Mach number approximation of the Navier-Stokes equation. Finally, we quantify the modulation of turbulence due to changes in fluid properties. In the simulations, the fluid is internally heated and the temperature at both channel walls is fixed, such that the friction Reynolds number based on wall quantities is Re τ = 395 for all cases investigated. We show that for a case with variable density ρ and viscosity µ, but constant semi-local Reynolds number Re * τ ≡  (ρ/ρ w )/(µ/µ w )Re τ (where bar and subscript w, denote Reynolds averaging and averaged wall quantity, respectively), across the whole channel height, the turbulent statistics exhibit quasi-similarity with constant property turbulent flows. For cases where Re * τRe τ across the channel, we found that quasi-similarity is maintained for cases with similar Re * τ distributions, even if their individual mean density and viscosity profiles substantially differ. With a decrease of Re * τ towards the channel center (Re * τ < Re τ ), we show that the anisotropy increases and the pre-multiplied stream-wise spectra reveal that this increase is associated with strengthening of the large scale streaks in the buffer layer. The opposite effect is observed when Re * τ increases towards the channel center. The present results provide an effective framework for categorizing turbulence modulation in wall-bounded flows with variable property effects, and can be applied to any Newtonian fluid that is heated or cooled. C 2015 AIP Publishing LLC. [http://dx

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“…These two values can significantly differ in the case of strong temperature fluctuations or in the case in which the constitutive relation for ψ is highly sensitive to the value of its argument, as is the case for turbulent flows at supercritical pressures [35]. In all flow cases considered here, this inconsistency in fluid property evaluations is limited and does not affect the results and our discussion.…”

Section: Base Flow Profilesmentioning

confidence: 87%

Linear stability of buffer layer streaks in turbulent channels with variable density and viscosity

et al. 2017

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We investigate the stability of streaks in the buffer layer of turbulent channel flows with temperature-dependent density and viscosity by means of linear theory. The adopted framework consists of an extended set of the Orr-Sommerfeld-Squire equations that accounts for density and viscosity nonuniformity in the direction normal to the walls. The base flow profiles for density, viscosity, and velocity are averaged from direct numerical simulations (DNSs) of fully developed turbulent channel flows. We find that the inner scaling based on semilocal quantities provides an effective parametrization of the effect of variable properties on the linearized flow. The spanwise spacing of optimal buffer layer streaks scales to λ z,opt ≈ 90 for all cases considered and the maximum energy amplification decreases, compared to the one for a flow with constant properties, if the semilocal Reynolds number Re τ increases away from the walls, consistently with less energetic streaks observed in DNSs of turbulent channels. A secondary stability analysis of the two-dimensional velocity profile formed by the mean turbulent velocity and the nonlinearly saturated optimal streaks predicts a streamwise instability mode with wavelength λ x,cr ≈ 230 in semilocal units, regardless of the fluid property distribution across the channel. The threshold for the onset of the secondary instability is reduced, compared to a constant property flow, if Re τ increases away from the walls, which explains the more intense ejection events reported in DNSs. The opposite behavior is predicted by the linear theory for decreasing Re τ , in accord with DNS observations. We finally show that the phase velocity of the critical mode of secondary instability agrees well with the convection velocity calculated by DNSs in the near-wall region for both constant and variable viscosity flows.

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Mean statistics of a heated turbulent pipe flow at supercritical pressure

Cited by 93 publications

References 30 publications

Scalar statistics in variable property turbulent channel flows

Scalar statistics in variable property turbulent channel flows

Semi-local scaling and turbulence modulation in variable property turbulent channel flows

Linear stability of buffer layer streaks in turbulent channels with variable density and viscosity

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