Numerical Study of Roughness Effects on a NACA0012 Airfoil Using a New Two-Equation Closure of the Rough Wall Layer Modeling

Measurements of the spanwise and wall-normal components of vorticity and their constituent velocity derivative fluctuations have been made in a turbulent boundary layer over a mesh-screen rough wall using a four-hot-wire vorticity probe. The measured spectra and variances of vorticity and velocity derivatives have been corrected for the effect of spatial resolution. The high-wavenumber behaviour of the spectra conforms closely with isotropy. Over most of the outer layer, the normalized magnitudes of the velocity derivative variances differ significantly from those over a smooth wall layer. The differences are such that the variances are much more nearly isotropic over the rough wall than on the smooth wall. This behaviour is consistent with earlier observations that the large-scale structure in this rough wall layer is more isotropic than that in a smooth wall layer. Isotropy-based approximations for the mean energy dissipation rate and mean enstrophy are consequently more reliable in this rough wall layer than in a smooth wall layer. In the outer layer, the vorticity variances are slightly larger than those over a smooth wall; reflecting structural differences between the two flows.

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Experimental and numerical study of wall layer development in a tribocharged fluidized bed

Journal of Fluid Mechanics ◽

10.1017/jfm.2018.412 ◽

2018 ◽

Vol 849 ◽

pp. 860-884 ◽

Cited By ~ 8

Author(s):

Petteri Sippola ◽

Jari Kolehmainen ◽

Ali Ozel ◽

Xiaoyu Liu ◽

Pentti Saarenrinne ◽

...

Keyword(s):

Pressure Drop ◽

Fluidized Bed ◽

Numerical Study ◽

Single Layer ◽

Wall Layer ◽

Small Scale ◽

Average Charge ◽

Particle Layer ◽

Column Wall ◽

Triboelectric Charging

The effects of triboelectricity in a small-scale fluidized bed of polyethylene particles were investigated by imaging the particle layer in the vicinity of the column wall and by measuring the pressure drop across the bed. The average charge on the particles was altered by changing the relative humidity of the gas. A triboelectric charging model coupled with a computational fluid dynamics–discrete element method (CFD-DEM) model was utilized to simulate gas–particle flow in the bed. The electrostatic forces were evaluated based on a particle–particle particle–mesh method, accounting for the surface charge on the insulating walls. It was found that simulations with fixed and uniform charge distribution among the particles capture remarkably well both the agglomeration of the particles on the wall and the associated decrease in the pressure drop across the bed. With a dynamic tribocharging model, the charging rate had to be accelerated to render the computations affordable. Such simulations with an artificial acceleration significantly over-predict charge segregation and the wall becomes rapidly sheeted with a single layer of strongly charged particles.

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A New Rough Wall Layer Modeling Using the Brinkman Equation in Turbulent Boundary Layers

46th AIAA Aerospace Sciences Meeting and Exhibit ◽

10.2514/6.2008-649 ◽

2008 ◽

Author(s):

Meng-Huang Lu ◽

William Liou

Keyword(s):

Boundary Layers ◽

Turbulent Boundary Layers ◽

Wall Layer ◽

Rough Wall ◽

Brinkman Equation

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Effect of Kinematic Operating Conditions on Ridge Deformation—Numerical Study With Experimental Comparison

Journal of Tribology ◽

10.1115/1.4034764 ◽

2016 ◽

Vol 139 (3) ◽

Author(s):

Ildikó Ficza ◽

Petr Šperka ◽

Ivan Křupka ◽

Martin Hartl

Keyword(s):

Numerical Study ◽

Operating Conditions ◽

Experimental Comparison ◽

Roughness Effects ◽

Mean Velocity ◽

Recent Experimental Work ◽

Theoretical Analyses ◽

Highly Loaded ◽

Contact Part ◽

Ehl Contact

The behavior of roughness features under rolling–sliding inside highly loaded elastohydrodynamically lubricated (EHL) contacts is studied in detail for many years now. In particular, the roughness deformation was subject to different theoretical analyses as well as experiments. A recent experimental work developed by Šperka et al. (2016, “Experimental Study of Roughness Effects in a Rolling–Sliding EHL Contact—Part I: Roughness Deformation,” Tribol. Trans., 59(2), pp. 267–276) studied the effect of kinematic operating conditions (mean velocity and slide to roll ratio) on the deformed profile of a ridge. The current paper presents results of full numerical simulations and their direct comparison to experiments in order to study the dependency of roughness deformation on the operating conditions. The assumption of non-Newtonian lubricant behavior seems to have a significant influence on the results as well. Results indicate that, in agreement with experiments, the variation of mean velocity causes changes in the deformed profiles of roughness while, on the other hand, the magnitude of slide to roll ratio (for sliding larger than ±50%) does not have influence on the size of the deformation.

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Rough Wall Layer Modeling Using the Brinkman Equation

5th AIAA Theoretical Fluid Mechanics Conference ◽

10.2514/6.2008-4241 ◽

2008 ◽

Author(s):

William Liou ◽

Meng-Huang Lu

Keyword(s):

Wall Layer ◽

Rough Wall ◽

Brinkman Equation

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Numerical study of passive and active flow separation control over a NACA0012 airfoil

Computers & Fluids ◽

10.1016/j.compfluid.2007.10.010 ◽

2008 ◽

Vol 37 (8) ◽

pp. 975-992 ◽

Cited By ~ 58

Author(s):

Hua Shan ◽

Li Jiang ◽

Chaoqun Liu ◽

Michael Love ◽

Brant Maines

Keyword(s):

Flow Separation ◽

Numerical Study ◽

Separation Control ◽

Flow Separation Control ◽

Naca0012 Airfoil ◽

Active Flow

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Numerical Study of Roughness Effects on a Turbine Stage Performance

Volume 5: Turbo Expo 2004, Parts A and B ◽

10.1115/gt2004-53750 ◽

2004 ◽

Cited By ~ 2

Author(s):

Young-Seok Kang ◽

Jae-Chun Yoo ◽

Shin-Hyoung Kang

Keyword(s):

Numerical Study ◽

Measured Data ◽

Suction Surface ◽

Roughness Effects ◽

Performance Variables ◽

High Profile ◽

Noticeable Reduction ◽

High Roughness ◽

Profile Loss ◽

Good Agreement

Turbine performance deteriorations due to blade surface roughness were numerically estimated. Numerical calculations were carried out for a low speed, single-stage axial turbine with a commercial CFD code, CFX-Tascflow, using a modified wall function boundary condition for rough surfaces. Two equivalent sand-grain roughness heights of 106μm (transitionally rough regime) and 400μm (fully rough regime) were considered. Two performance variables, stage work coefficient and efficiency were compared with the measured data. The calculated results showed qualitatively good agreement with the measured data. The calculated and measured performance variables deteriorated as the roughness height increased. High roughness induced small changes in deviation angles of the stator and rotor. These changes in the deviation angles result in a noticeable reduction in the work coefficient. One dimensional analysis shows that the stator deviation angle is more sensitive to the work coefficient reduction. On the other hand, the stage efficiency reduction due to the roughness was accountable with an additional profile loss due to the roughness. Loss generation in the stator stage was approximately 10% higher than that of the rotor due to very high profile loss occurred on the suction surface trailing edge of the stator.

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