LDA Measurements in Rough Surface ZPG Turbulent Boundary layers

2006 ◽  
Author(s):  
Brian Brzek ◽  
Rau´l Bayoa´n Cal ◽  
Gunnar Johansson ◽  
Luciano Castillo
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Laser Doppler Anemometry ◽  
Single Point ◽  
Roughness Parameter ◽  
Reynolds Stresses ◽  
Experimental Conditions ◽  
Boundary Layer Equations ◽  
Entire Boundary ◽  
Boundary Layer Development

A new set of experiments have been performed in order to study the effects of the upstream conditions and the surface roughness on a zero pressure gradient turbulent boundary layer. In order to properly capture the x-dependence of the single point statistics, consecutive measurements of 11 streamwise locations were performed. These 2-D Laser Doppler Anemometry (LDA) measurements enable us to use the full boundary layer equations in order to calculate the skin friction and determine the boundary layer development which is not possible in the majority of experiments on rough surfaces. It will be shown that for fixed experimental conditions (i.e., fixed upstream wind tunnel speed, trip wire, etc), the velocity deficit profiles collapse for each of the scalings investigated but only the Zagarola/Smits scaling (1998) could collapse all the different experimental conditions into a single curve. In addition, the Reynolds stresses were increasingly affected by the surface roughness as the roughness parameter, k+, increased. Moreover, it was found that the shape of the Reynolds stress profiles was very different throughout the entire boundary layer, particularly the < u2 > component. This is likely the result of the flow becoming more isotropic for increased k+, and will be seen in the anisotropy coefficients. Moreover, increased production of < u2 > and < uv > due to roughness is also seen throughout the entire boundary layer although its overall role in the changing shape of the < u2 > profiles still needs to be determined. The effect of roughness on the boundary layer parameters is also evident and their x-dependence is also shown.

scholarly journals Coastal Boundary Layer Characteristics of Wind, Turbulence, and Surface Roughness Parameter over the Thumba Equatorial Rocket Launching Station, India

2014 ◽  
Vol 2014 ◽  
pp. 1-21 ◽  
Author(s):  
K. V. S. Namboodiri ◽  
Dileep Puthillam Krishnan ◽  
Rahul Karunakaran Nileshwar ◽  
Koshy Mammen ◽  
Nadimpally Kiran kumar
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Wind Direction ◽  
Roughness Parameter ◽  
Turbulent Heat ◽  
Surface Roughness Parameter ◽  
South West Monsoon ◽  
Wind Turbulence ◽  
Coastal Boundary Layer ◽  
Coastal Boundary

The study discusses the features of wind, turbulence, and surface roughness parameter over the coastal boundary layer of the Peninsular Indian Station, Thumba Equatorial Rocket Launching Station (TERLS). Every 5 min measurements from an ultrasonic anemometer at 3.3 m agl from May 2007 to December 2012 are used for this work. Symmetries in mesoscale turbulence, stress off-wind angle computations, structure of scalar wind, resultant wind direction, momentum flux (M), Obukhov length (L), frictional velocity (u*), w-component, turbulent heat flux (H), drag coefficient (CD), turbulent intensities, standard deviation of wind directions (σθ), wind steadiness factor-σθ relationship, bivariate normal distribution (BND) wind model, surface roughness parameter (z0), z0 and wind direction (θ) relationship, and variation of z0 with the Indian South West monsoon activity are discussed.

INVESTIGATION OF SINGLE-POINT DRESSING OVERLAP RATIO AND DIAMOND-ROLL DRESSING INTERFERENCE ANGLE ON SURFACE ROUGHNESS IN GRINDING

2010 ◽  
Vol 34 (2) ◽  
pp. 295-308 ◽  
Author(s):  
Akram Saad ◽  
Robert Bauer ◽  
Andrew Warkentin
Keyword(s):  
Surface Roughness ◽  
Material Removal Rate ◽  
Empirical Model ◽  
Material Removal ◽  
Removal Rate ◽  
Single Point ◽  
Experimental Conditions ◽  
Workpiece Surface ◽  
Different Depths ◽  
Overlap Ratio

This paper investigates the effect of both single-point and diamond-roll dressing techniques on the workpiece surface roughness in grinding. Two empirical surface roughness models are studied – one that incorporates single-point dressing parameters, and another that incorporates diamond-roll dressing parameters. For the experimental conditions used in this research, the corresponding empirical model coefficients are found to have a linear relationship with the inverse of the overlap ratio for single-point dressing and the interference angle for diamond-roll dressing. The resulting workpiece surface roughness models are then experimentally validated for different depths of cut, workpiece speeds and dressing conditions. In addition, the models are used to derive a relationship between overlap ratio for single-point dressing, and interference angle for diamond-roll dressing such that both dressing techniques produce a similar surface finish for a given material removal rate.

Boundary Layers on a Rotating Rough Disk

1994 ◽  
Author(s):  
Ali Heydari ◽  
Ramin Miryan ◽  
Saeid Sharifi
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Parabolic Equations ◽  
Roughness Parameter ◽  
Rotating Disk ◽  
Turbulent Fluid Flow ◽  
Uniform Wall Temperature ◽  
Curve Fit ◽  
Uniform Wall ◽  
Finite Difference Solution

Abstract In this paper the turbulent fluid flow over a rotating disk with roughness is considered. The disk is assumed to be at uniform wall temperature. The surface roughness is assumed to influence the turbulent boundary layer by adding a roughness parameter height k. Boundary-layer approximation reduces the elliptic Navier-Stockes equations to parabolic equations, where the Keller-Cebeci method of finite-difference solution is used to solve the resulting system of partial-differential equations. The resulting curve-fit equations to the numerically calculated results for three regions of laminar, transition and turbulent flow is shown to be consistent to those obtained for flow over a flat plate or inside a circular cylinder. Calculations for various surface roughness parameters are made and results are presented.

DNS of a turbulent boundary layer with surface roughness

2013 ◽  
Vol 729 ◽  
pp. 603-637 ◽  
Author(s):  
James Cardillo ◽  
Yi Chen ◽  
Guillermo Araya ◽  
Jensen Newman ◽  
Kenneth Jansen ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Turbulent Boundary Layer ◽  
Normal Component ◽  
Shear Stresses ◽  
Reynolds Stresses ◽  
Multi Scale ◽  
Smooth Case ◽  
Pod Analysis ◽  
Low Order

AbstractA pioneer direct numerical simulation (DNS) of a turbulent boundary layer at $R{e}_{\theta } = 2077{{\unicode{x2013}}}2439$, was performed, on a rough surface and with a zero pressure gradient (ZPG). The boundary layer was subjected to transitional, 24-grit sandpaper surface roughness, with a roughness parameter of ${k}^{+ } \simeq 11$. The computational method involves a synergy of the dynamic multi-scale approach devised by Araya et al. (2011) for prescribing inlet turbulent boundary conditions and a new methodology for mapping high-resolution topographical surface data into a computational fluid dynamics (CFD) environment. It is shown here that the dynamic multi-scale approach can be successfully extended to simulations which incorporate surface roughness. The DNS results demonstrate good agreement with the laser Doppler anemometry (LDA) measurements performed by Brzek et al. (2008) and Schultz & Flack (2003) under similar conditions in terms of mean velocity profiles, Reynolds stresses and flow parameters, such as the skin friction coefficient, boundary and momentum thicknesses. Further, it is demonstrated that the effects of the surface roughness on the Reynolds stresses, at the values of $R{e}_{\theta } = 2077{{\unicode{x2013}}}2439$, are scale-dependent. Roughness effects were mainly manifested up to $y/ \delta \approx 0. 1$. Generally speaking, it was observed that inner peak values of Reynolds stresses increased when considering outer units. However, decreases were seen in inner units. In the outer region, the most significant differences between the present DNS smooth and rough cases were computed in the wall-normal component $\langle {v}^{\prime 2} \rangle $ of the Reynolds stresses and in the Reynolds shear stresses $\langle {u}^{\prime } {v}^{\prime } \rangle $ in outer units. From the resulting flow fields a proper orthogonal decomposition (POD) analysis is performed and the effects of the surface roughness are distinctly observed in the most energetic POD modes. The POD analysis shows that the surface roughness causes a redistribution of the kinetic energy amongst the POD modes with energy being shifted from low-order to high-order modes in the rough case versus the smooth case. Also, the roughness causes a marked decrease in the characteristic wavelengths observed in the POD modes, particularly in the streamwise component of the velocity field. Low-order modes of the streamwise component demonstrated characteristic wavelengths of the order of $3\delta $ in the smooth case, whereas the same modes for the rough case demonstrated characteristic wavelengths of only $\delta $.

The Combined Effects of Surface Roughness with Upstream Wakes on the Boundary Layer Development of an Ultra-High-Lift LPT Blade

2017 ◽  
Vol 34 (1) ◽  
Author(s):  
Sun Shuang ◽  
Lei Zhijun ◽  
Lu Xin’gen ◽  
Zhang Yanfeng ◽  
Zhu Junqiang
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Combined Effects ◽  
High Lift ◽  
Linear Cascade ◽  
Low Pressure Turbine ◽  
Boundary Layer Development ◽  
Large Measurement ◽  
Lp Turbine ◽  
Layer Development

AbstractThe combined effects of upstream wakes and surface roughness on boundary layer development have been investigated experimentally to improve the performance of ultra-high-lift low-pressure turbine (LPT) blades. The measurement was performed on a linear cascade with an ultra-high-lift LP turbine profile named IET-LPTA with a Zweifel loading coefficient of about 1.4. The wakes were simulated by the moving cylindrical bars upstream of the cascade. The surface roughness was achieved using sandpaper strips which were placed into the slot incised on the blades surfaces. Three types of slots combined with three types of roughness heights formed a large measurement matrix. The roughness with a height of 8.82 μm (1.05×10

Characterizing Surface Roughness Effects on Supersonic Turbulent Boundary Layers

2021 ◽  
Author(s):  
Rozie Zangeneh
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Practical Importance ◽  
Rough Wall ◽  
Reynolds Stresses ◽  
Roughness Effects ◽  
Mean Velocity ◽  
Modeling Tools ◽  
Turbulent Statistics ◽  
The Impact

Abstract Flight vehicles traveling at supersonic or hypersonic speeds are vulnerable to the onset of surface roughness, which can result in changes in the state of the boundary layer, ultimately affecting the performance of the vehicle. While the majority of the wetted surface area of a vehicle is relatively smooth, every vehicle will contain roughness on some level. The concept of similarity between smooth- and rough-wall flows is of great practical importance as most computational and analytical modeling tools rely on it either explicitly or implicitly in predicting flows over rough walls. While a number of important questions have yet to be answered, significant progress has been made in the understanding of flows over rough surfaces in recent years. This paper will be conducting numerical research in rough-wall-bounded turbulent flows in supersonic regimes. Wall-modeled Large Eddy Simulation (WMLES) on a flat plate with various roughness ratios will be conducted at M∞ = 2 to evaluate the boundary layer responses. These responses will be characterized in ensemble averaged mean velocity characteristics as well as turbulent intensity responses through the Reynolds Stresses. The second goal is to characterize the streamwise development of mechanical distortions in the domain. In addition, the near-wall coherent structures will be analyzed to determine the impact of roughness effects. The mean and turbulent statistics scaled by the roughness friction velocity will be compared to other results.

Simulation of Transitional Boundary-Layer Development on a Highly-Loaded Turbine Cascade With Advanced RANS Modeling

2003 ◽  
Author(s):  
D. Keith Walters ◽  
James H. Leylek
Keyword(s):  
Boundary Layer ◽  
Single Point ◽  
Turbulence Models ◽  
Boundary Layer Transition ◽  
Mean Velocity ◽  
Layer Transition ◽  
New Model ◽  
Boundary Layer Development ◽  
Layer Development ◽  
Highly Loaded

This paper documents computational simulations of the flow over a modern, highly-loaded turbine vane, including boundary-layer transition. Accurate prediction of transition has traditionally been difficult for commonly available RANS-based turbulence models. The present simulations used an advanced version of a three-equation eddy viscosity model recently developed and documented by the current authors. The new model is an elliptic single-point method, developed based on considerations of the universal character of pre-transitional boundary layers that have recently been published in the open literature. Simulations were performed at an engine-realistic chord Reynolds number (2.3×105) and with varying freestream turbulence intensities of 0.6, 10, and 19.5%. Detailed comparisons are made within the developing boundary layer, on both the suction and pressure surfaces, between the simulations and high-fidelity experimental measurements that have been previously documented in the open literature. Comparison of both mean velocity and Reynolds stress profiles indicates that the new model shows potential for predicting boundary layer development, including development of pre-transitional fluctuations and subsequent breakdown to turbulence.

Unsteady dissipation measurements on a flat plate subject to wake passing

2003 ◽  
Vol 217 (4) ◽  
pp. 413-419 ◽  
Author(s):  
R. D. Stieger ◽  
H. P. Hodson
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Laser Doppler Anemometry ◽  
Boundary Layer Separation ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
High Lift ◽  
Pressure Distributions ◽  
Lp Turbine ◽  
Wake Passing

Boundary layer measurements were performed on a flat plate with an imposed pressure gradient typical of a high-lift low-pressure (LP) turbine blade and subject to incoming turbulent wakes shed from a moving bar wake generator. A multiple-orientation one-dimensional laser doppler anemometry (LDA) technique was used to measure the ensemble-average mean flow and Reynolds stresses. These ensembleaverage measurements were used to calculate the boundary layer dissipation, thereby providing unprecedented experimental evidence of the loss-reducing mechanisms associated with wake-induced transition. The benign character of the calmed zone was confirmed and the early stages of boundary layer separation were found to have laminar levels of dissipation. A deterministic natural transition phenomenon was identified between wake passing events, highlighting the existence of natural transition phenomena in LP turbine style pressure distributions.

LDA-Measurements of Transitional Flows Induced by a Square Rib

2001 ◽  
Vol 124 (1) ◽  
pp. 108-117 ◽  
Author(s):  
S. Becker ◽  
C. M. Stoots ◽  
K. G. Condie ◽  
F. Durst ◽  
D. M. McEligot
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Boundary Layers ◽  
Laser Doppler Anemometry ◽  
Plate Boundary ◽  
Index Of Refraction ◽  
Wall Region ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Turbulent Statistics

New fundamental measurements are presented for the transition process in flat plate boundary layers downstream of two-dimensional square ribs. By use of laser Doppler anemometry (LDA) and a large Matched-Index-of-Refraction (MIR) flow system, data for wall-normal fluctuations and Reynolds stresses were obtained in the near wall region to y+<0.1 in addition to the usual mean streamwise velocity component and its fluctuation. By varying velocity and rib height, the experiment investigated the following range of conditions: k+=5.5 to 21, 0.3<k/δ1<1,180<Rek<740,6×104<Rex,k<1.5×105,ReΘ660,−125<x−xk/k<580. Consequently, results covered boundary layers which retained their laminar characteristics through those where a turbulent boundary layer was established shortly after reattachment beyond the forcing rib. For “large” elements, evolution of turbulent statistics of the viscous layer for a turbulent boundary layer y+<∼30 was rapid even in flows where the mean velocity profile still showed laminar behavior.

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