scholarly journals Application of Displacement Height and Surface Roughness Length to Determination Boundary Layer Development Length over Stepped Spillway

Water ◽  
2014 ◽  
Vol 6 (12) ◽  
pp. 3888-3912 ◽  
Author(s):  
Xiangju Cheng ◽  
John Gulliver ◽  
Dantong Zhu
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Roughness Length ◽  
Stepped Spillway ◽  
Development Length ◽  
Displacement Height ◽  
Surface Roughness Length ◽  
Boundary Layer Development ◽  
Layer Development

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

scholarly journals Reduced Sea-Surface Roughness Length at a Coastal Site

Atmosphere ◽  
2021 ◽  
Vol 12 (8) ◽  
pp. 991
Author(s):  
Yuncheng He ◽  
Jiyang Fu ◽  
Pak Wai Chan ◽  
Qiusheng Li ◽  
Zhenru Shu ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Atmospheric Boundary Layer ◽  
Roughness Length ◽  
Sea Surface ◽  
Marine Atmospheric Boundary Layer ◽  
Coastal Site ◽  
Surface Roughness Length ◽  
Sea Surface Roughness ◽  
Roughness Lengths

Sea-surface roughness length is a key parameter for characterizing marine atmospheric boundary layer. Although aerodynamic roughness lengths for homogeneous land and open water surfaces have been examined extensively, the extension of relevant knowledge to the highly inhomogeneous coastal area is problematic due to the complex mechanisms controlling coastal meteorology. This study presented a lidar-based observational analysis of sea-surface roughness length at a coastal site in Hong Kong, in which the wind data recorded from March 2012 to November 2015 were considered and analyzed. The results indicated the turning of wind near the land-sea boundary, leading to a dominative wind direction parallel to the coastline and an acceleration in wind. Moreover, the roughness lengths corresponding to two representative azimuthal sectors were compared, in which the roughness lengths for the onshore wind sector (i.e., 120°–240°) appear to be larger than the constant value (z0 = 0.2 mm) recommended in much existing literature, whereas the values for the alongshore wind sector (i.e., 60°–90°) are significantly smaller, i.e., about two orders of magnitude less than that of a typical sea surface. However, it is to be noted that the effect of atmospheric stability, which is of crucial importance in governing the marine atmospheric boundary layer, is not taken into account in this study.

scholarly journals The Making of the New European Wind Atlas, Part 1: Model Sensitivity

2020 ◽  
Author(s):  
Andrea N. Hahmann ◽  
Tija Sile ◽  
Björn Witha ◽  
Neil N. Davis ◽  
Martin Dörenkämper ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Wind Speed ◽  
Planetary Boundary Layer ◽  
Land Surface ◽  
Roughness Length ◽  
Wrf Model ◽  
Model Sensitivity ◽  
Surface Roughness Length ◽  
Wind Climate

Abstract. This is the first of two papers that documents the creation of the New European Wind Atlas (NEWA). It describes the sensitivity analysis and evaluation procedures that formed the basis for choosing the final setup of the mesoscale model simulations of the wind atlas. An optimal combination of model setup and parameterisations was found for simulating the climatology of the wind field at turbine-relevant heights with the Weather Research and Forecasting (WRF) model. Initial WRF model sensitivity experiments compared the wind climate generated by using two commonly used planetary boundary layer schemes and were carried out over several regions in Europe. They confirmed that the largest differences in annual mean wind speed at 100 m above ground level mostly coincide with areas of high surface roughness length and not with the location of the domains or maximum wind speed. Then an ensemble of more than 50 simulations with different setups for a single year was carried out for one domain covering Northern Europe, for which tall mast observations were available. Many different parameters were varied across the simulations, for example, model version, forcing data, various physical parameterisations and the size of the model domain. These simulations showed that although virtually every parameter change affects the results in some way, significant changes on the wind climate in the boundary layer are mostly due to using different physical parameterisations, especially the planetary boundary layer scheme, the representation of the land surface, and the prescribed surface roughness length. Also, the setup of the simulations, such as the integration length and the domain size can considerably influence the results. The degree of similarity between winds simulated by the WRF ensemble members and the observations was assessed using a suite of metrics, including the Earth Mover's Distance (EMD), a statistic that measures the distance between two probability distributions. The EMD was used to diagnose the performance of each ensemble member using the full wind speed distribution, which is important for wind resource assessment. The most realistic ensemble members were identified to determine the most suitable configuration to be used in the final production run, which is fully described and evaluated in the second part of this study.

Effect of Surface Roughness on Loss Behaviour, Aerodynamic Loading and Boundary Layer Development of a Low-Pressure Gas Turbine Airfoil

2010 ◽  
Author(s):  
Marco Montis ◽  
Reinhard Niehuis ◽  
Andreas Fiala
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Low Pressure ◽  
Test Facility ◽  
Hot Wire ◽  
Wire Probe ◽  
Aerodynamic Loading ◽  
Boundary Layer Development ◽  
Layer Development ◽  
Effect Of Surface

Aerodynamic measurements on the linear low-pressure turbine cascade T106C were conducted in a high speed test facility, in order to investigate the effect of surface roughness on loss behaviour, aerodynamic loading, and boundary layer development. Three different roughnesses were investigated, with a ratio of the center line average roughness to the profile chord of 0.8·10−5, 5·10−5 and 25·10−5. Tests were carried out under design outlet Mach number (Ma2th = 0.6), outlet Reynolds number ranging from Re2th = 5·104 to Re2th = 7·105 and inlet turbulence level Tu1 = 3% and Tu1 = 6%. The flow field downstream of the cascade and the loading distribution on the profiles were measured for each investigated operating point using five hole probes and surface static pressure taps. Additional measurements with a hot-wire probe in the suction surface (SS) boundary layer were also conducted, in order to investigate the differences in boundary layer development due to surface roughness. From loss and blade loading measurements it was found that roughness has no influence on the pressure distribution on the profile, although the highest investigated roughness produces a significant loss reduction at low Reynolds numbers. Hot-wire probe surveys show that at Re2th = 9·104 the boundary layer for the highest roughness immediately upstream of the flow separation point on the SS is substantially thinner than for the middle roughness and the smooth profile.

scholarly journals The making of the New European Wind Atlas – Part 1: Model sensitivity

2020 ◽  
Vol 13 (10) ◽  
pp. 5053-5078 ◽  
Author(s):  
Andrea N. Hahmann ◽  
Tija Sīle ◽  
Björn Witha ◽  
Neil N. Davis ◽  
Martin Dörenkämper ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Wind Speed ◽  
Planetary Boundary Layer ◽  
Roughness Length ◽  
Wrf Model ◽  
Model Sensitivity ◽  
Surface Roughness Length ◽  
Wind Climate ◽  
Physical Parameterizations

Abstract. This is the first of two papers that document the creation of the New European Wind Atlas (NEWA). It describes the sensitivity analysis and evaluation procedures that formed the basis for choosing the final setup of the mesoscale model simulations of the wind atlas. The suitable combination of model setup and parameterizations, bound by practical constraints, was found for simulating the climatology of the wind field at turbine-relevant heights with the Weather Research and Forecasting (WRF) model. Initial WRF model sensitivity experiments compared the wind climate generated by using two commonly used planetary boundary layer schemes and were carried out over several regions in Europe. They confirmed that the most significant differences in annual mean wind speed at 100 m a.g.l. (above ground level) mostly coincide with areas of high surface roughness length and not with the location of the domains or maximum wind speed. Then an ensemble of more than 50 simulations with different setups for a single year was carried out for one domain covering northern Europe for which tall mast observations were available. We varied many different parameters across the simulations, e.g. model version, forcing data, various physical parameterizations, and the size of the model domain. These simulations showed that although virtually every parameter change affects the results in some way, significant changes in the wind climate in the boundary layer are mostly due to using different physical parameterizations, especially the planetary boundary layer scheme, the representation of the land surface, and the prescribed surface roughness length. Also, the setup of the simulations, such as the integration length and the domain size, can considerably influence the results. We assessed the degree of similarity between winds simulated by the WRF ensemble members and the observations using a suite of metrics, including the Earth Mover's Distance (EMD), a statistic that measures the distance between two probability distributions. The EMD was used to diagnose the performance of each ensemble member using the full wind speed and direction distribution, which is essential for wind resource assessment. We identified the most realistic ensemble members to determine the most suitable configuration to be used in the final production run, which is fully described and evaluated in the second part of this study (Dörenkämper et al., 2020).

Assessing the Influence of Aerosol on Radiation and Its Roles in Planetary Boundary Layer Development

2021 ◽  
Vol 35 (2) ◽  
pp. 384-392
Author(s):  
Zhigang Cheng ◽  
Yubing Pan ◽  
Ju Li ◽  
Xingcan Jia ◽  
Xinyu Zhang ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Planetary Boundary Layer ◽  
Boundary Layer Development ◽  
Layer Development

Numerical Simulation of Turbine Blade Boundary Layer and Heat Transfer and Assessment of Turbulence Models

1997 ◽  
Vol 119 (4) ◽  
pp. 794-801 ◽  
Author(s):  
J. Luo ◽  
B. Lakshminarayana
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Low Reynolds Number ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Bypass Transition ◽  
Boundary Layer Development ◽  
Low Reynolds ◽  
Layer Development

The boundary layer development and convective heat transfer on transonic turbine nozzle vanes are investigated using a compressible Navier–Stokes code with three low-Reynolds-number k–ε models. The mean-flow and turbulence transport equations are integrated by a four-stage Runge–Kutta scheme. Numerical predictions are compared with the experimental data acquired at Allison Engine Company. An assessment of the performance of various turbulence models is carried out. The two modes of transition, bypass transition and separation-induced transition, are studied comparatively. Effects of blade surface pressure gradients, free-stream turbulence level, and Reynolds number on the blade boundary layer development, particularly transition onset, are examined. Predictions from a parabolic boundary layer code are included for comparison with those from the elliptic Navier–Stokes code. The present study indicates that the turbine external heat transfer, under real engine conditions, can be predicted well by the Navier–Stokes procedure with the low-Reynolds-number k–ε models employed.

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