Near-wall damping in model predictions of separated flows

Skote, Martin; Wallin, Stefan

doi:10.1080/10618562.2016.1194402

Cited by 8 publications

(2 citation statements)

References 25 publications

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“…None of the four has a systematic derivation. (SeeSkote & Wallin (2016) for a review of current wall-damping functions, and an attempt to generalise them into a single model applicable to decelerating and separated flows.) With pressure gradient, −u′v′ deviates from u τ 2…”

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confidence: 99%

Numerical study of turbulent separation bubbles with varying pressure gradient and Reynolds number

2018

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A family of cases each containing a small separation bubble is treated by direct numerical simulation (DNS), varying two parameters: the severity of the pressure gradients, generated by suction and blowing across the opposite boundary, and the Reynolds number. Each flow contains a well-developed entry region with essentially zero pressure gradient, and all are adjusted to have the same value for the momentum thickness, extrapolated from the entry region to the centre of the separation bubble. Combined with fully defined boundary conditions this will make comparisons with other simulations and turbulence models rigorous; we present results for a set of eight Reynolds-averaged Navier–Stokes turbulence models. Even though the largest Reynolds number is approximately 5.5 times higher than in a similar DNS study we presented in 1997, the models have difficulties matching the DNS skin friction very closely even in the zero pressure gradient, which complicates their assessment. In the rest of the domain, the separation location per se is not particularly difficult to predict, and the most definite disagreement between DNS and models is near reattachment. Curiously, the better models tend to cluster together in their predictions of pressure and skin friction even when they deviate from the DNS, although their eddy-viscosity levels are widely different in the outer region near the bubble (or they do not rely on an eddy viscosity). Stratford’s square-root law is satisfied by the velocity profiles, both at separation and reattachment. The Reynolds-number range covers a factor of two, with the Reynolds number based on the extrapolated momentum thickness equal to approximately 1500 and 3000. This allows tentative estimates of the improvements that even higher values will bring to the model comparisons. The solutions are used to assess models through pressure, skin friction and other measures; the flow fields are also used to produce effective eddy-viscosity targets for the models, thus guiding turbulence-modelling work in each region of the flow.

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confidence: 99%

Numerical study of turbulent separation bubbles with varying pressure gradient and Reynolds number

2018

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“…Wall functions that use the pressure-gradient (or some non-dimensional representation of it) have been previously explored in the context of incompressible flows by (for e.g.) Skote & Wallin [70]. Eddy viscosity formulations that use a pressure-gradient parameter such as the one given by Duprat et al [26] and Nituch et al [56] have shown promising results in adverse pressure-gradient, separated flows.…”

Section: Formulationmentioning

confidence: 99%

Wall modeled LES of compressible flows at non-equilibrium conditions

Mettu

Subbareddy

2018

2018 Fluid Dynamics Conference

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METTU, BALACHANDRA REDDY. Wall Modeled LES of Compressible Flows in Non-Equilibrium Conditions. (Under the direction of Pramod Subbareddy.)A turbulent boundary layer is composed of a wide range of length scales and time scales. To resolve all these scales of motion, as with a DNS or traditional wall resolved LES, the grid sizes required scale roughly as the square/cube of the Reynolds number (Re). These requirements make high Re flows computationally very expensive. By modeling the effect of the motions close to the wall, as is proposed in wall modeled LES (WMLES) methods, the computation of high Re flows can be made significantly cheaper. To date, WMLES has been relatively less studied in application with strong compressibility effects.In this study, we implement state-of-the-art wall models for these flows and examine the different challenges which are common to high-speed flow applications: isothermal cold wall conditions, the transition to turbulence, and shock boundary layer interactions (SBLI). It is observed that for cold-wall flows, a more empirical "mixed" scaling for the length scale appearing in the eddy viscosity formulation outperforms the classical semi-local scaling for obtaining predictions of heat-flux and skin-friction. For transitional flows, we develop a modified transition sensor that gave robust predictions for the high Mach number cases we examined. We find that the more computationally expensive non-equilibrium model with an eddy viscosity formulation based on the pressure gradient outperformed the standard equilibrium model for skin-friction predictions in SBLIs. A sensor for detecting regions of non-equilibrium flow was developed based on the resolved Reynolds stress. By using this sensor and switching to an exchange location closer to the wall in the non-equilibrium region for the equilibrium model gave skin-friction and heat flux results close to or even better than the non-equilibrium model at a far cheaper cost. WMLES was performed for SBLI at moderate to high Re with different wall temperature conditions. It was observed that WMLES was able to capture the expansion and shrinking of the separation bubble size when the wall was heated and cooled. Also observed was that using WMLES the low-frequency characteristics of SBLI at high Re was now possible. As a whole, it was seen that WMLES can become a promising tool for exploring the complex physics involved in turbulent high-speed flows at a significantly lower cost than wall resolved LES/DNS and with much higher fidelity compared to pure RANS simulations.

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Artificial neural network-based wall-modeled large-eddy simulations of turbulent channel and separated boundary layer flows

Lee

2023

Aerospace Science and Technology

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Near-wall damping in model predictions of separated flows

Cited by 8 publications

References 25 publications

Numerical study of turbulent separation bubbles with varying pressure gradient and Reynolds number

Numerical study of turbulent separation bubbles with varying pressure gradient and Reynolds number

Wall modeled LES of compressible flows at non-equilibrium conditions

Artificial neural network-based wall-modeled large-eddy simulations of turbulent channel and separated boundary layer flows

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