INVESTIGATION OF SURFACE ROUGHNESS IMPACT ON MEAN WIND FLOW USING RNG k-ε MODEL

2016 ◽  
Vol 78 (9) ◽  
Author(s):  
Sheikh Ahmad Zaki Shaikh Salim ◽  
Ahmad Zaki Jaafar ◽  
Ahmad Faiz Mohammad ◽  
Sukri Mohamed Mat Ali ◽  
Azli Abd Razak
Keyword(s):  
Surface Roughness ◽  
Streamwise Velocity ◽  
Navier Stokes ◽  
Future Research ◽  
Small Scale ◽  
Wind Flow ◽  
Roughness Elements ◽  
The Impact ◽  
Scale Roughness ◽  
Packing Densities

Wind flow in the urban boundary layer is influenced by both large- and small-scale surface roughness. In this study, Reynolds-averaged Navier-Stokes simulations using the renormalisation group (RNG) k-ε model were performed to study the wind flow in square arrays with small-scale roughness elements at the front and back of cubical obstacles at packing densities of 25.0% and 30.9%. The presence of small-scale roughness reduces streamwise velocity but increases turbulent kinetic energy. Moreover, small vortices are formed within the canopy because of small-scale roughness. The generated streamwise velocity profiles are similar at packing densities of 25.0% and 30.9%, but the drag coefficient is higher in the latter case. In brief, the impact of small-scale roughness on urban wind flow is considerable. The results of this study can contribute to future research on wind flow, particularly in the urban environment.  

scholarly journals Unmanned Aerial Systems for Investigating the Polar Atmospheric Boundary Layer—Technical Challenges and Examples of Applications

Atmosphere ◽  
2020 ◽  
Vol 11 (4) ◽  
pp. 416 ◽  
Author(s):  
Astrid Lampert ◽  
Barbara Altstädter ◽  
Konrad Bärfuss ◽  
Lutz Bretschneider ◽  
Jesper Sandgaard ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Low Temperatures ◽  
Open Water ◽  
Future Research ◽  
Small Scale ◽  
Unmanned Aerial Systems ◽  
Research Activities ◽  
Aerial Systems ◽  
The Impact

Unmanned aerial systems (UAS) fill a gap in high-resolution observations of meteorological parameters on small scales in the atmospheric boundary layer (ABL). Especially in the remote polar areas, there is a strong need for such detailed observations with different research foci. In this study, three systems are presented which have been adapted to the particular needs for operating in harsh polar environments: The fixed-wing aircraft M 2 AV with a mass of 6 kg, the quadrocopter ALICE with a mass of 19 kg, and the fixed-wing aircraft ALADINA with a mass of almost 25 kg. For all three systems, their particular modifications for polar operations are documented, in particular the insulation and heating requirements for low temperatures. Each system has completed meteorological observations under challenging conditions, including take-off and landing on the ice surface, low temperatures (down to −28 ∘ C), icing, and, for the quadrocopter, under the impact of the rotor downwash. The influence on the measured parameters is addressed here in the form of numerical simulations and spectral data analysis. Furthermore, results from several case studies are discussed: With the M 2 AV, low-level flights above leads in Antarctic sea ice were performed to study the impact of areas of open water within ice surfaces on the ABL, and a comparison with simulations was performed. ALICE was used to study the small-scale structure and short-term variability of the ABL during a cruise of RV Polarstern to the 79 ∘ N glacier in Greenland. With ALADINA, aerosol measurements of different size classes were performed in Ny-Ålesund, Svalbard, in highly complex terrain. In particular, very small, freshly formed particles are difficult to monitor and require the active control of temperature inside the instruments. The main aim of the article is to demonstrate the potential of UAS for ABL studies in polar environments, and to provide practical advice for future research activities with similar systems.

Inferring Ice/Ocean Surface Roughness from Horizontal Current Measurements

1989 ◽  
Vol 111 (2) ◽  
pp. 155-159 ◽  
Author(s):  
M. G. McPhee
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Local Stress ◽  
Horizontal Stress ◽  
Current Speed ◽  
Small Scale ◽  
Horizontal Current ◽  
Similarity Model ◽  
Scale Roughness ◽  
Shear Production

Turbulence measurements in the underice boundary layer from two Arctic drift stations are used to develop a method for estimating the small-scale roughness, zo, of the ice underside from horizontal current and current variance, sampled at one level. Horizontal variance is shown to be well correlated with turbulent kinetic energy (TKE). Measurements also indicate that at depths where turbulence is fully developed to the surface roughness, shear production of TKE is approximately in balance with viscous dissipation, so that the magnitude of local horizontal stress is proportional to flow variance. A similarity model is used to extrapolate local stress to the interface, and zo is estimated from the logarithmic profile for current speed. The method has application for using remote data buoys, equipped with “smart” current meters, for mapping the underice roughness.

Heat Transfer Generated by the Interaction of Single and Multiple Tandem Jets in Crossflow

2010 ◽  
Author(s):  
Amina Radhouane ◽  
Nejla Mahjoub ◽  
Hatem Mhiri ◽  
George Lepalec ◽  
Philippe Bournot
Keyword(s):  
Heat Transfer ◽  
Stokes Equations ◽  
Reynolds Stress Model ◽  
Navier Stokes ◽  
Uniform Grid ◽  
Cooling Power ◽  
Small Scale ◽  
Fluid Composition ◽  
Navier Stokes Equations ◽  
The Impact

“Twin jets in Crossflow” is a common configuration that finds application in several large and/or small scale industrial fields. The interest in such a configuration is further enhanced by its dependence in several parameters, that may be geometric, dynamic, thermal, or relative to the handled fluid composition. We propose to focus in the present work on the effect of the number of the emitted jets on the generated heat transfer, in presence of an unchanged uniform crossflow. To reach this goal, single, double and triple jet configurations were simulated, based upon the resolution of the Navier Stokes equations by means of the RSM (Reynolds Stress Model) second order turbulent closure model, together with a non uniform grid system particularly tightened near the emitting nozzles. After validation, we tried to find out the impact of the number of the handled jets on their cooling “power” by tracking the temperature distribution of the resulting flowfield. Since in practically all applications we are in need of higher efficiencies and then of higher operating temperatures, we are constantly concerned about not going beyond the shielding material melting temperature. If the use of cooling jets proves to be efficient, this may bring a significant progress in the technological field.

Experimental Modeling of Wind-Driven Bin-by-Bin Resuspension Factors of Freshly Fallen Radionuclides After an Energetic Release From a Radiological Dispersal Device

2015 ◽  
Vol 1 (1) ◽  
Author(s):  
Sharman Perera ◽  
Edward Waller ◽  
Ali Akhtar
Keyword(s):  
Surface Roughness ◽  
Wind Tunnel ◽  
Lanthanum Oxide ◽  
Experimental Modeling ◽  
Small Scale ◽  
Particle Sizes ◽  
Particle Resuspension ◽  
Measuring Devices ◽  
Radiological Dispersal ◽  
The Impact

Small-scale experiments were carried out to characterize the resuspension factor of radioactive lanthanum oxide powder in an environmentally controlled wind tunnel, with the majority using particle sizes less than 10 μm in order to assess the impact of wind resuspension stresses and surface roughness conditions on resuspension. Operational principles of the measuring devices used in the radionuclide resuspension experiments and corresponding uncertainties are discussed. The average bin-by-bin particle resuspension factors (ki) for particle sizes, in the range of 0.25–7.00 μm and 7.00–12.5 μm for downwind fallout locations, were calculated and are reported here as 1.14×10−3 1/m and 4.39×10−2 1/m, respectively.

scholarly journals INVESTIGATION HYPERBOLIC PARABOLOID SHELL IN THE WIND TUNNEL AND COMPARISON WITH NUMERICAL SIMULATIONS

2018 ◽  
Vol 64 ◽  
Author(s):  
V.V. Stojanov ◽  
S. Jgalli
Keyword(s):  
Numerical Simulation ◽  
Wind Tunnel ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Wind Flow ◽  
Hyperbolic Paraboloid ◽  
Ansys Fluent ◽  
Navier Stokes Equations ◽  
Basic Model ◽  
The Impact

There are different ways to determine aerodynamic parameters, using analytical and experimental data for analyzing the behavior of structures when exposed to wind load. To date, the most developed is considered a numerical method for determining the characteristics of the above methods, based on the numerical solution of the Navier-Stokes equations. The accuracy of the results obtained using such a calculation method and obtaining the values of aerodynamic forces has increased due to the revision of mathematical models and the development of software complexes for the discretization of object bodies. This article gives an analytical overview of the results of research in the field of study the impact of wind loads on hypar (shell square in plan with the form of a hyperbolic paraboloid). The features of the investigated forms a discretization surface depending on pressure coefficients obtained in foreign literatures. Particular attention is paid to the numerical determination of aerodynamic coefficients on the surfaces of a hyperbolic paraboloid. The results were discussed and the nature of the distribution of coefficients depending on the angle of attack of the wind. Achieved analytical comparison computer modeling turbulent wind flows, based on solving the Reynolds equations arising from the use of averaging the Navier-Stokes equations. The basic model of turbulence such as: k-ε Standard Model; MMK; DBN; Shear-Stress Transport k-ω model; Transition k-kl-ω model. The possibility of choosing one or another model depending on the properties and characteristics of the wind flow is analyzed, for application in numerical simulation of wind flow around hyperbolic shells. The same was done, a comparative analysis of the results of physical testing in a wind tunnel with a numerical simulation in Ansys Fluent.

scholarly journals A MODIFIED TWO-SCALE MICROWAVE SCATTERING MODEL FOR A GAUSSIAN-DISTRIBUTED CONDUCTING ROUGH SURFACE

2018 ◽  
Vol XLII-3 ◽  
pp. 2141-2146
Author(s):  
F. Yu ◽  
H. Wang ◽  
Z. Y. Chen
Keyword(s):  
Surface Roughness ◽  
Rough Surface ◽  
Large Scale ◽  
Incident Angle ◽  
Wavelet Packet ◽  
Small Scale ◽  
Backscattering Coefficient ◽  
Microwave Scattering ◽  
Scattering Model ◽  
Scale Roughness

A modified two-scale microwave scattering model (MTSM) was presented to describe the scattering coefficient of natural rough surface in this paper. In the model, the surface roughness was assumed to be Gaussian so that the surface height <i>z(x, y)</i> can be split into large-scale and small-scale components relative to the electromagnetic wavelength by the wavelet packet transform. Then, the Kirchhoff Model (KM) and Small Perturbation Method (SPM) were used to estimate the backscattering coefficient of the large-scale and small-scale roughness respectively. Moreover, the ‘tilting effect’ caused by the slope of large-scale roughness should be corrected when we calculated the backscattering contribution of the small-scale roughness. Backscattering coefficient of the MTSM was the sum of backscattering contribution of both scale roughness surface. The MTSM was tested and validated by the advanced integral equation model (AIEM) for dielectric randomly rough surface, the results indicated that, the MTSM accuracy were in good agreement with AIEM when incident angle was less than 30&amp;deg; (<i>&amp;theta;<sub>i</sub></i>&amp;thinsp;&amp;lt;30&amp;deg;) and the surface roughness was small (<i>ks</i>&amp;thinsp;=&amp;thinsp;0.354).

Preparing for PhD: exploring doctoral students’ preparation strategy

2020 ◽  
Vol 11 (1) ◽  
pp. 89-106 ◽  
Author(s):  
Ahmad Thamrini Fadzlin Syed Mohamed ◽  
Ahmad Fahimi Amir ◽  
Nur Khadirah Ab. Rahman ◽  
Emily Abd Rahman ◽  
Afifah Quraishah Abdul Nasir
Keyword(s):  
Doctoral Students ◽  
Academic Career ◽  
Future Research ◽  
Small Scale ◽  
Content Type ◽  
Preparation Phase ◽  
Personal Level ◽  
Preparation Strategy ◽  
Professional Doctorates ◽  
The Impact

Purpose The purpose of this paper is to give insight on the important preparation task needed to be considered by prospective PhD candidates prior to the start of their study. As pursuing and obtaining a higher degree qualification is becoming more eminent for those who want to advance their academic career, crucial preparation is needed before embarking on the doctoral quest. Design/methodology/approach A small-scale study of the PhD experience was carried out in a public university in Malaysia using semi-structured in-depth interviews with eight successful doctoral students representing three different faculties to assess respondents’ experiences concerning the preparation aspect, challenges faced and strategies used to overcome the problem. Findings From the interview data, three overarching themes emerged: motives, task and financial and health as important dominators that could influence a successful venture of a PhD journey. Research limitations/implications As the present research respondents were few, further research with bigger number of respondents may shed better light in identifying other important aspect in preparation for PhD. The authors are unable, in the space of this paper, to fully explore the implications of the data, and the work of others that it builds on, for the future of professional doctorates or other types of PhD awards. As professional doctorates are fully concentrated on their professional endeavour, i.e. nursing and education, the preparation needed may include different groundwork. In addition, this study was carried out in Malaysia, where the system may not necessarily share the same characteristics to other doctoral systems in other countries. Cultural differences, the impact of age, gender and race, were other variables that could be weighed by future research in the same area. Practical implications The university’s graduate office should line-up courses to inform future doctoral candidates on the aspect of preparation at personal level that the students need to carry out. Social implications The study provides new views where potential doctoral students should be helped and guided to become more consciously aware of their decision in pursuing a higher degree. This paper provides suggestions on the guidelines of the initial preparation needed before embarking on a PhD journey and managing their own learning. Originality/value The paper establishes the important aspect of the preparation phase needed to be considered by future doctoral students before pursuing their doctoral quest.

scholarly journals In-Hospital Mortality Following Traumatic Brain Injury Among Older Medicare Beneficiaries, Comparing Statin Users With Nonusers

2017 ◽  
Vol 33 (6) ◽  
pp. 225-236 ◽  
Author(s):  
Bilal Khokhar ◽  
Linda Simoni-Wastila ◽  
Julia F. Slejko ◽  
Eleanor Perfetto ◽  
Min Zhan ◽  
...  
Keyword(s):  
Older Adults ◽  
Traumatic Brain Injury ◽  
Brain Injury ◽  
Hospital Mortality ◽  
Health Concern ◽  
Future Research ◽  
Small Scale ◽  
Medicare Beneficiaries ◽  
The Impact ◽  
Statin Use

Background: Traumatic brain injury (TBI) is a significant public health concern for older adults. Small-scale human studies have suggested pre-TBI statin use is associated with decreased in-hospital mortality following TBI, highlighting the need for large-scale translational research. Objective: To investigate the relationship between pre-TBI statin use and in-hospital mortality following TBI. Methods: A retrospective study of Medicare beneficiaries 65 and older hospitalized with a TBI during 2006 to 2010 was conducted to assess the impact of pre-TBI statin use on in-hospital mortality following TBI. Exposure of interest included atorvastatin, fluvastatin, lovastatin, pravastatin, rosuvastatin, and simvastatin. Beneficiaries were classified as current, recent, past, and nonusers of statins prior to TBI. The outcome of interest was in-hospital mortality. Logistic regression was used to obtain odds ratios (ORs) and 95% confidence intervals (CIs) comparing current, recent, and prior statin use to nonuse. Results: Most statin users were classified as current users (90%). Current atorvastatin (OR = 0.88; 95% = CI 0.82, 0.96), simvastatin (OR = 0.84; 95% CI = 0.79, 0.91), and rosuvastatin (OR = 0.79; 95% CI = 0.67, 0.94) use were associated with a significant decrease in the risk of in-hospital mortality following TBI. Conclusions: In addition to being the most used statins, current use of atorvastatin, rosuvastatin, and simvastatin was associated with a significant decrease in in-hospital mortality following TBI among older adults. Future research must include clinical trials to help exclude the possibility of a healthy user effect in order to better understand the impact of statin use on in-hospital mortality following TBI.

Performance and Emission Assessment on a 3kW Micro Gas Turbine: Comparison of RANS and LES Predictions

2021 ◽  
Author(s):  
Alessio Pappa ◽  
Francesco F. Nicolosi ◽  
Antoine Verhaeghe ◽  
Laurent Bricteux ◽  
Massimiliano Renzi ◽  
...  
Keyword(s):  
Gas Turbine ◽  
Industrial Applications ◽  
Combustion Stability ◽  
Navier Stokes ◽  
Small Scale ◽  
Significant Discrepancy ◽  
Performance And Emission ◽  
Micro Gas Turbine ◽  
Inlet Conditions ◽  
The Impact

Abstract Computational fluid dynamics represent a powerful tool to assess the performance of a combustor and identify possible issues/instabilities, helping thus e.g. to investigate the impact of advanced cycle modifications on the combustion in mGTs. The steady Reynolds-averaged Navier-Stokes (RANS) approach is still mostly used in this framework. With growing computational power, Large Eddy Simulation (LES) has gained more interest. LES provides higher details concerning flow structures and can better predict possible instabilities, specifically needed for advanced cycle modelling. On the other hand, LES remain rather challenging for real industrial applications. This work aims at providing an answer whether the advantages of LES justify the much higher computational costs. The objective of the present study is thus to assess the combustion performance and emissions of a typical small-scale 3.2 kWe micro gas turbine (mGT), using steady RANS and LES for various fuels. In this framework, a comparison of RANS and LES approaches (two levels of fidelity) is performed on a typical industrial case, to point out the strengths and weakness of each method with regard to industrial and research needs. The results show that both RANS (at a reduced cost) and LES can accurately predict the time-averaged trends of the main performance parameters, like temperature levels and emissions, also using various non-conventional inlet conditions. For the accurate prediction of the instabilities, the LES approach stands out as this approach takes into account the time-variation of the different quantities. Finally, a significant discrepancy has been observed between the CO levels provided by RANS and LES approaches where LES is overestimating the level of CO in the exhaust gases. Whereas it is difficult for LES to compete with convincing results provided by RANS, especially in the prediction of global emissions at reduced simulation cost, the LES strengths come out especially in flame and combustion stability analysis.

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