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The present study numerically investigates turbulent momentum transfer in concentric coaxial (annular) pipe flow with small radius ratios (η=Ri/Ro=0.1,0.04,0.02)$(\eta ={R}_{i}/{R}_{o}=0.1,0.04,0.02)$. To model the flow, a stochastic one‐dimensional turbulence (ODT) model formulated for cylindrical geometry is used that provides full‐scale resolution along a representative radial coordinate. The present investigation extends the model validation by Tsai et al. (PAMM, 22:e202200272, 2023), to radius ratios smaller than 0.1 and addresses boundary layers with strong spanwise curvature effects. The focus is on the assessment and analysis of statistical flow features in the vicinity of the inner cylinder wall, particularly in cases with small radius ratios. Following Boersma & Breugem (Flow Turbul. Combust., 86:113–127, 2011), classical boundary‐layer and mixing‐length theory is utilized to analyze the model predictions. The results demonstrate that the ODT model captures leading‐order curvature and mixing‐length effects by its physics‐compatible construction. Utilizing the model for extrapolation to high Reynolds numbers inaccessible to conventional high‐fidelity numerical approaches shows that curvature effects persist and nonlocally affect the entire boundary layer. The model results provide support for a spanwise‐curvature‐modified wall function. [ABSTRACT FROM AUTHOR]

Reynolds‐averaged Navier–Stokes simulation (RaNS) is state‐of‐the‐art for numerical analysis of complex flows at high Reynolds number. Standalone RaNS may yield a reasonable estimate of the wall‐shear stress and turbulent drag if a proper wall‐function is prescribed, but detailed turbulence statistics cannot be obtained, especially at the wall. This lack in modeling is addressed here by a stochastic deconvolution strategy based on a stochastic one‐dimensional turbulence (ODT) model. Here, a one‐way coupling strategy is proposed in which a forcing term is computed from the balanced RaNS solution that is in turn utilized in the ODT model. The temporally developing ODT solution exhibits turbulent perturbations but relaxes toward the local RaNS solution due to resolved molecular‐diffusive processes. It is demonstrated that the approach is able to recover the distribution of positive wall‐shear stress fluctuations in turbulent channel flow. When formulated as post‐processing tool, it is suggested that RaNS can be enhanced by ODT providing economical means for local high‐fidelity numerical modeling based on a low‐fidelity flow solution. [ABSTRACT FROM AUTHOR]

Simultaneous momentum and passive scalar transfer in weakly heated pressure‐driven turbulent concentric annular pipe flow is numerically investigated using the cylindrical formulation of the stochastic one‐dimensional turbulence (ODT) model, which is utilized here as standalone tool. In the present study, we focus on the model calibration for heated annular pipes based on recent reference direct numerical simulations (DNS) from Bagheri and Wang (Int. J. Heat Fluid Flow 86, 108725, 2020; Phys. Fluids 33, 055131, 2021). It is shown that the model is able to individually capture scalar and momentum transfer, but not both equally well at the same time. We attribute this to less dissimilar scalar and momentum transport in the model at the low Reynolds number investigated. It is argued that the model prefers a fully developed turbulent state due to its construction. Nevertheless, it is demonstrated that ODT is able to reasonably capture the radial inner‐outer asymmetry of the scalar and momentum boundary layers which yields better predictive capabilities than wall‐function‐based approaches. [ABSTRACT FROM AUTHOR]

Small-scale processes in atmospheric boundary layers are typically not resolved due to cost constraints but modeled based on physical relations with the resolved scales, neglecting expensive backscatter. This lack in modeling is addressed in the present study with the aid of the one-dimensional turbulence (ODT) model. ODT is applied as stand-alone column model to numerically investigate stratification effects in long-lived transient Ekman flows as canonical example of polar boundary layers by resolving turbulent winds and fluctuating temperature profiles on all relevant scales of the flow. We first calibrate the adjustable model parameters for neutral cases based on the surface drag law which yields slightly different optimal model set-ups for finite low and moderate Reynolds numbers. For the stably stratified cases, previously calibrated parameters are kept fixed and the model predictions are compared with various reference numerical simulations and also observations by an exploitation of boundary layer similarity. ODT reasonably captures the temporally developing flow for various prescribed stratification profiles, but fails to fully capture the near-surface laminarization by remaining longer in a fully developed turbulent state, which suggests preferential applicability to high-Reynolds-number flow regimes. Nevertheless, the model suggests that large near-surface turbulence scales are primarily affected by the developing stratification due to scale-selective buoyancy damping which agrees with the literature. The variability of the wind-turning angle represented by the ensemble of stratified cases simulated covers a wider range than reference reanalysis data. The present study suggests that the vertical-column ODT formulation that is highly resolved in space and time can help to accurately represent multi-physics boundary-layer and subgrid-scale processes, offering new opportunities for analysis of very stable polar boundary layer and atmospheric chemistry applications. [ABSTRACT FROM AUTHOR]

The incompressible temporally developing turbulent boundary layer (TBL) is analysed using the map-based stochastic one-dimensional turbulence (ODT) model. The TBL is a canonical flow problem, which is, in the present study, formed by a planar moving wall and a free stream at rest. An understanding of this idealised flow is of fundamental relevance for the numerical analysis of turbulent boundary-layer-type flows. In the present ODT simulations, the flow variables are resolved on all scales along a wall-normal, one-dimensional domain. These variables are evolved by a deterministic and a stochastic process. The latter models the effect of turbulent advection and pressure fluctuations, whereas the former represents molecular diffusion. The model is appropriate for high Reynolds numbers for which the turbulence field exhibits a broad range of scales and is notionally featureless. We show that ODT is able to capture salient features of the TBL by comparing the various statistics with available reference direct numerical simulation (DNS) results for different bulk Reynolds numbers in the range 250 ≤ R e b ≤ 2000 using fixed model parameters. The influence of the model parameters is analysed for R e b = 1000 and optimal parameter values are provided. The results discussed in this paper suggest that ODT is an economical and reasonably accurate approach for the simulation of transient turbulent boundary-layer-type flows. [ABSTRACT FROM AUTHOR]

In this paper we overcome a key problem in an otherwise highly potential approach to study turbulent flows, ODTLES (One‐Dimensional Turbulence Large Eddy Simulation). From a methodological point of view, ODTLES is an approach in between Direct Numerical Simulations (DNS) and averaged/filtered approaches like RANS (Reynolds Averaged Navier‐Stokes) or LES (Large Eddy Simulations). In ODTLES, a set of 1D ODT models is embedded in a coarse grained 3D LES. On the ODT scale, the turbulent advection is modeled as a sequence of stochastic eddy events, also known as triplet maps, while the other (deterministic) terms are fully resolved in space (along the ODT‐line) and time. Schmidt et al. first (2008) introduced ODTLES and Gonzalez et al. (2011) applied the model for a variety of wall‐bounded flow problems. Although the results were notable for a first proof of concept, the numerical methods used are subject to debate. First of all, an unstable discretization for the large scale 3D advective terms was used, as shown by Glawe (2015). This scheme can be stabilized by reducing the CFL number for the explicitly discretized LES terms down to the order of the small scale ODT time step, but this of course reduces the advantage of the ODTLES multi‐scale approach. The stochastic ODT eddies were also allowed to overlap two LES cells introducing an artificial smoothing (stabilizing) effect. Glawe (2015) limited the overlap consistently to one LES cell and used a stable Runge Kutta (RK) discretization, maintaining, however the low CFL number problem. In this paper we adapt a new implicit/explicit (IMEX) time scheme to ODTLES in order to remedy the small CFL number issue. For the problems investigated, the results indicate a performance increase of the IMEX scheme by a factor of 17 based on the ratio of applied CFL numbers. This allowed simulations of a turbulent channel flow with characteristic friction Reynolds number Reτ=2040 on one Banana Pi single board computer. We compare results to available DNS data and discuss in general the efficiency and potential of ODTLES for high Reynolds number flows. In this paper we overcome a key problem in an otherwise highly potential approach to study turbulent flows, ODTLES (One‐Dimensional Turbulence Large Eddy Simulation). From a methodological point of view, ODTLES is an approach in between Direct Numerical Simulations (DNS) and averaged/filtered approaches like RANS (Reynolds Averaged Navier‐Stokes) or LES (Large Eddy Simulations). In ODTLES, a set of 1D ODT models is embedded in a coarse grained 3D LES. On the ODT scale, the turbulent advection is modeled as a sequence of stochastic eddy events, also known as triplet maps, while the other (deterministic) terms are fully resolved in space (along the ODT‐line) and time... [ABSTRACT FROM AUTHOR]

The turbulent asymptotic suction boundary layer is studied using a one-dimensional turbulence (ODT) model. ODT is a fully resolved, unsteady stochastic simulation technique. While flow properties reside on a one-dimensional domain, turbulent advection is represented using mapping events whose occurrences are governed by a random process. Due to its reduced spatial dimensionality, ODT achieves major cost reductions compared to three-dimensional (3D) simulations. A comparison to recent direct numerical simulation (DNS) data at moderate Reynolds number (Re=u∞/v0= 333, whereu∞andv0are the free stream and suction velocity, respectively) suggests that the ODT model is capable of reproducing several velocity statistics, i.e. mean velocity and turbulent kinetic energy budgets, while peak turbulent stresses are under-estimated by ODT. Variation of the Reynolds number in the rangeRe∈ [333,400,500,1000] shows that ODT can reproduce various trends observed as a result of increased suction in turbulent asymptotic suction boundary layers, i.e. the reduction of Reynolds stresses and enhanced skin friction. While up toRe= 500 our results can be directly compared to recent LES data, the simulation atRe= 1000 is currently not feasible through full 3D simulations, hence ODT may assist the design of future DNS or LES simulations at larger Reynolds numbers. [ABSTRACT FROM AUTHOR]

We numerically investigate the Reynolds number dependency of the transport of a passive scalar in incompressible, fully‐developed turbulent channel flows. The stochastic one‐dimensional turbulence (ODT) model is used to make such numerical simulation feasible up to the friction Reynolds number Reτ = uτ δ/ν ≈ 5200 (channel half‐height δ, friction velocity uτ, kinematic viscosity ν) in the Schmidt number range 1 ≤ Sc = ν/Γ = 400 (mass diffusion coefficient Γ). The ODT simulations exhibit a turbulent boundary layer for which we show that the simulated mass transfer coefficient K+ follows the functional dependency suggested by Schwertfirm and Manhart, Int. J. Heat Fluid Flow 28, 1204–1214 (2007). The agreement is good for Sc ≤ 25 but a different scaling is obtained for Sc ≥ 49 investigated. [ABSTRACT FROM AUTHOR]

We investigate incompressible temporally developing turbulent boundary layers for the first time using the One‐Dimensional Turbulence (ODT) model. ODT is spatially fully resolved along the 1D domain, only turbulent advection is represented by stochastic mapping events. We compare the mean and root mean square velocity profiles with the Direct Numerical Simulations (DNS) results for bulk Reynolds numbers, Reb = 500 and 1000 (Reb = Ubd/ν, where ν is the kinematic viscosity, Ub is the velocity provided at the bottom wall and d is the trip wire diameter for experiments). The study demonstrates that ODT has the capability to systematically investigate developing boundary layers. [ABSTRACT FROM AUTHOR]

A map-based stochastic approach, One-Dimensional Turbulence (ODT), is applied to analyze the incompressible spatially developing turbulent boundary layer (SBL). In the present study, the SBL is formed by a plane moving wall and a free stream at rest. The flow variables are resolved on all scales along a 1-D domain. A deterministic process represents the molecular diffusion and a stochastic process is modeling the effect of turbulent advection and pressure fluctuations. Due to the reduced dimensions in the model, it achieves major cost reductions as compared to the full 3-D simulations and is, thus, able to explore large parameter regimes. The simulations are presented for momentum thickness Reynolds numbers, Re θ , varied in the range Re θ ≈ 1968 - 8000. We have investigated various features related to the SBL, such as mean, root mean square, Reynolds shear stress, skewness, flatness and pre-multiplied velocity profiles and skin friction coefficient and shape factor, all for two bulk velocities using ODT and compared our results to the available reference Direct Numerical Simulations (DNS) and large-eddy simulations (LES) results. We have further compared the results for spatial and temporal ODT formulations used to investigate the turbulent boundary layer with the reference data at matched Re θ . The comparison presented suggests that ODT is a reasonably accurate approach for the simulations of the spatially developing turbulent boundary layers which can be further improved to yield accurate statistics at high Reynolds number by implementing Fourier transformation of the kernels which in the present formulation of the model is not implemented. [ABSTRACT FROM AUTHOR]

Abstract: A stochastic modeling approach, the so‐called One‐Dimensional Turbulence (ODT), is used to study passive scalar transport in incompressible, fully‐developed, turbulent channel flows up to very high Schmidt numbers Sc = ν/Γ ∼ 104 (kinematic viscosity ν, scalar diffusivity Γ). Good agreement is obtained between ODT and Direct Numerical Simulation (DNS) results with respect to the mean, the fluctuation statistics, and the dimensionless mass transfer coefficient K+. ODT yields the mass transfer coefficient to become independent of the Reynolds number at high Schmidt numbers, which is similar to reference laboratory measurements and DNS. The present ODT results exhibit the power law K+ ∝ Sc−0.65 with a scaling exponent that is only slightly larger than in the reference laboratory measurements and DNS. The results obtained suggests that ODT can be a versatile tool for turbulent transport modeling in a wide range of physical parameters. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Friction factor enhancements in pipe-flows subject to fixed electric fields are evaluated using the stochastic One-Dimensional Turbulence (ODT) model. To that extent, low Mach asymptotics are used to derive the leading order effects of the governing equations in electrohydrodynamic (EHD) flows considering low mobility ratios. Temporal and spatial ODT formulations are then carried out for three different Reynolds numbers (Re = 3000 , Re = 4000 and Re = 5000) at a set of electrohydrodynamic numbers in the range 0 ≤ N EHD ≤ 600. The ODT simulation results are compared to published experimental data on Darcy friction factor enhancements of Nelson et al. (1990). The results signalize the importance of the developing flow for the EHD-enhanced drag. On one hand, the ratio N EHD 2/Re2 characterizes the enhancement. On the other hand, the developing flow and the laminar-to-turbulent transition also have an important contribution to the friction factor. The ODT results presented here show that reduced order models can deliver relevant insights in otherwise numerically challenging flow simulations, therefore aiding the quantitative analysis of experimental observations in EHD flows. [ABSTRACT FROM AUTHOR]

• We introduce an extension of the spatial ODT formulation (S-ODT), in order to study a variable density internal air flow. • S-ODT results are compared to the results of a traditional temporal ODT formulation (T-ODT) and to reference DNS data. • For bulk quantities, both the T-ODT and S-ODT formulations have a similar performance in comparison to DNSs. • For the evaluation of radial distributions, the S-ODT formulation clearly outperforms the T-ODT formulation. A novel spatial formulation of the One-Dimensional Turbulence (ODT) model is applied to a vertical pipe-flow with heat transfer, analogous to the Direct Numerical Simulation (DNS) performed by Bae et al. [Phys. Fluids 18, (075102) (2006)]. The framework presented here is an extension for radially confined domains of the cylindrical ODT spatial formulation for low Mach number flows with variable density. The variable density simulations for air (Prandtl number P r = 0.71) are performed at an initial bulk Reynolds number R e b , 0 , D N S = 6000 and Grashof number G r 0 , D N S = 6.78 × 10 6. ODT results are presented for both the spatial formulation introduced in this work and the standard temporal formulation for cylindrical flows introduced by Lignell et al. [Theor. Comput. Fluid Dyn. 32, 4 (2018), pp. 495–20]. Streamwise bulk profiles and radial profiles at specific streamwise positions for the temporal and spatial formulations are in good agreement with the DNS results from Bae et al. For the present application, the spatial formulation yields physically better results in comparison to the temporal formulation. Overall, the findings in the original work of Bae et al. were corroborated with ODT. Although the framework proposed in this work is not a compressible framework and has some clear limitations regarding conservation properties, we suggest its use for future studies in the low Mach number variable density regime. [ABSTRACT FROM AUTHOR]