An Analytical Study of the Effects of Surface Roughness on Boundary-Layer Transition

Merkle, Charles L.; Kubota, T.; Ko, Denny R. S.

doi:10.21236/ada004786

Cited by 32 publications

(17 citation statements)

References 7 publications

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“…The boundary layer may be differently developed for different air intake manifold geometry. In addition, the surface roughness of the intake manifold may determine the pattern of the boundary layer (Merkle et al, 1977). Comparison of the results in Figure 11 shows a slight improvement in the flow coefficient as compared to simulation with a 204-mm intake manifold particularly at L/D ratios of greater than 0.10.…”

Section: Investigation Of the Boundary Layer Within The Intake Manifoldmentioning

confidence: 95%

Study of Flow in Air-Intake System for A Single-Cylinder Go-Kart Engine

Sulaiman¹,

Murad²,

Ibrahim³

et al. 2010

Int J Automot Mech Eng

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Intake-air manifolds have a major effect on a vehicle's engine performance and emission of noise and pollutants. Differences in engine outputs and applications require different designs of intake-air manifolds in order to achieve the best volumetric efficiency and thus the best engine performance. In the present work, the flow characteristics of air flowing in various designs of air-intake manifold of a 200-cc fourstroke Go-Kart engine are studied. The study is done by three dimensional simulations of the flow of air within six designs of air-intake manifold into the combustion chamber by using commercial CFD software, Fluent version 6.2. The simulation results are validated by an experimental study performed using a flow bench. The study reveals that the variations in the geometry of the air-intake system can result in a difference of up to 20% in the mass flow rate of air entering the combustion chamber.

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Section: Investigation Of the Boundary Layer Within The Intake Manifoldmentioning

confidence: 95%

Study of Flow in Air-Intake System for A Single-Cylinder Go-Kart Engine

Sulaiman¹,

Murad²,

Ibrahim³

et al. 2010

Int J Automot Mech Eng

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“…The relationship between the height of the roughness element and the flow disturbance induced is not easily correlated. 6 Roughness elements shorter than the height of the viscous sublayer generally have little effect on the transition process as the disturbances are dissipated away due to the high levels of viscous damping. Additionally as the boundary layer does not have a constant thickness, the effects cannot be generalized along the boundary layer of a rough surface.…”

Section: B Roughness Effectsmentioning

confidence: 99%

Analysis of the Impact of Leading Edge Surface Degradation on Wind Turbine Performance

Langel

Chow

Hurley

et al. 2015

33rd Wind Energy Symposium

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Over time it has been reported wind turbine power output can diminish below manufacturers promised levels. This is clearly undesirable from an operator standpoint, and can also put pressure on turbine companies to make up the difference. A likely explanation for the discrepancy in power output is the contamination of the leading edge due to environmental conditions creating surfaces much coarser than intended. To examine the effects of airfoil leading edge roughness, a comprehensive study has been performed both experimentally and computationally on a NACA 633 − 418 airfoil. A description of the experimental setup and test matrix are provided, along with an outline of the computational roughness amplification model used to simulate rough configurations. The experimental investigation serves to provide insight into the changes in measurable airfoil properties such as lift, drag, and boundary layer transition location. The computational effort is aimed at using the experimental results to calibrate a roughness model that has been implemented in an unsteady RANS solver. Furthermore, a blade element momentum code was used to assess the impact on the performance of a turbine as whole due to discrepancies in clean vs. soiled airfoil characteristics. The results have implications in predicting the power loss due to leading edge surface roughness, and can help to establish an upper bound on admissible surface contamination levels.

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“…Merkle et al [8] found that the presence of surface roughness affects the laminar velocity profile and decreases the transitional Reynolds number by a number of experiments. Mala et al [9] study the effects of the surface roughness on laminar flow in microtubes and considered it in terms of a roughness-viscosity function.…”

Section: Introductionmentioning

confidence: 99%

Optimization of machining parameters for micro-machining nozzle based on characteristics of surface roughness

Cai

Liu

Shi

et al. 2015

Int J Adv Manuf Technol

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Machined surface roughness has significant effects on the performance of micro-nozzles, which are fabricated by micro-machining. Machining process parameters greatly affect surface roughness, for that the manufacturers need to obtain optimal operating parameters. In this paper, machining parameters are optimized for micro-machining nozzle based on the characteristics of surface roughness. First, roughness model of nozzle milling with ball-end mill is presented. A case of nozzle surface is then given to verify the reliability of the roughness model proposed. Second, influences of surface roughness on nozzle average outlet velocity and thrust efficiency are investigated through computational fluid dynamics (CFD) analysis. It is found that vortical flow generates gradually with increasing of surface roughness, which leads to wasted energy increasing. When roughness value reaches a certain threshold, vortical flow is formed, which significantly reduces nozzle performances of velocity and thrust efficiency. Finally, micro-orthogonal machining experiments are performed. It is shown that the remarkable factor influencing the surface roughness of micro-nozzle is axial depth of cut.

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An Analytical Study of the Effects of Surface Roughness on Boundary-Layer Transition

Cited by 32 publications

References 7 publications

Study of Flow in Air-Intake System for A Single-Cylinder Go-Kart Engine

Study of Flow in Air-Intake System for A Single-Cylinder Go-Kart Engine

Analysis of the Impact of Leading Edge Surface Degradation on Wind Turbine Performance

Optimization of machining parameters for micro-machining nozzle based on characteristics of surface roughness

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