Study on the Downburst Field Characteristics under the Influence of Two-Dimensional Continuous Mountains at Different Distance

2014 ◽  
Vol 580-583 ◽  
pp. 3111-3114
Author(s):  
Yi Sun ◽  
Yuan Ze Wu ◽  
Hai Tao Shi ◽  
Bai Feng Ji
Keyword(s):  
Numerical Simulation ◽  
Boundary Layer ◽  
Wind Field ◽  
Strong Wind ◽  
Two Dimensional ◽  
Field Characteristic ◽  
Main Factors ◽  
Cfd Numerical Simulation ◽  
The Impact

Downburst is an outburst strong wind on or near the ground, and its wind field characteristics are significantly different from boundary layer winds. Continuous mountains at different distance are one of the main factors for the influence of downburst wind field characteristic. In this thesis, the changes of the wind field characteristics under the influence of continuous mountains at different distance after the downburst happened are studied by CFD numerical simulation. The impact of downburst is analysed and summarized through the charts.

Influence of Engine Cabin Simplification on Aerodynamic Characteristics of Car

2014 ◽  
Vol 1042 ◽  
pp. 188-193 ◽  
Author(s):  
Xing Jun Hu ◽  
Jing Chang
Keyword(s):  
Numerical Simulation ◽  
Aerodynamic Drag ◽  
Aerodynamic Characteristics ◽  
Thin Plates ◽  
Average Thickness ◽  
Two Dimensional ◽  
Engine Cooling ◽  
Aerodynamic Drag Coefficient ◽  
Simulation Results ◽  
The Impact

In order to analyze the impact of engine cabin parts on aerodynamic characteristics, the related parts are divided into three categories except the engine cooling components: front thin plates (average thickness of 2mm), bottom-suspension and interior panels. The aerodynamic drag coefficient (Cd) were obtained upon the combination schemes consisting of the three types of parts by numerical simulation. Results show that Cd by simulation is closer to the test value gained by the wind tunnel experiment when front thin plates were simplified to the two-dimensional interface with zero thickness. The error is only 5.23%. Meanwhile this scheme reduces grid numbers, thus decreasing the calculating time. As the front thin plates can guide the flow, there is no difference on the Cd values gained from the model with or without bottom-suspension or interior panels when the engine cabin contains the front thin plates; while only both bottom-suspension and interior panels are removed, the Cd value can be reduced when the cabin doesn’t contain the front thin plates.

Influence of Exhaust Nozzle Geometry on the Jet Potential Core Development

2015 ◽  
Vol 811 ◽  
pp. 145-151 ◽  
Author(s):  
Daniel Eugeniu Crunteanu ◽  
Valentin Ionut Misirliu ◽  
Oana Dumitrescu ◽  
Bogdan Gherman
Keyword(s):  
Numerical Simulation ◽  
Boundary Layer ◽  
Boundary Conditions ◽  
Turbulence Model ◽  
Nozzle Geometry ◽  
Turbofan Engine ◽  
Potential Core ◽  
The Third ◽  
The Impact

In this paper, a numerical simulation was performed on a scale turbofan engine nozzle to asses the influence of two nozzle configurations over the flow performance while the nozzle is situated at a certain distance from the ground. The turbulence model chosen for this numerical simulation was SST k-ω to capture boundary layer detachment and jet attachment to the ground. For this analysis two different computational domains where considered, while for the third case, boundary conditions for secondary inlet where modified. To assess the impact of these geometry changes a comparison between cases is made at different location in the domain.

scholarly journals Microphysical Structure of the Marine Boundary Layer under Strong Wind and Spray Formation as Seen from Simulations Using a 2D Explicit Microphysical Model. Part I: The Impact of Large Eddies

2011 ◽  
Vol 68 (10) ◽  
pp. 2366-2384 ◽  
Author(s):  
J. Shpund ◽  
M. Pinsky ◽  
A. Khain
Keyword(s):  
Boundary Layer ◽  
Marine Boundary Layer ◽  
Surface Fluxes ◽  
Cloud Base ◽  
Small Scale ◽  
Sea Spray ◽  
Strong Wind ◽  
Spray Droplets ◽  
The Impact ◽  
Large Eddies

Abstract The effects of large eddies (LE) on the marine boundary layer (MBL) microphysics and thermodynamics is investigated using a 2D Lagrangian model with spectral bin microphysics including effects of sea spray. The 600 m × 400 m MBL computational area is covered by 3750 adjacent interacting Lagrangian parcels moving in a turbulent-like flow. A turbulent-like velocity field is designed as a sum of a high number of harmonics with random time-dependent amplitudes and different wavelengths including large eddies with scales of several hundred meters. The model explicitly calculates diffusion growth/evaporation, collisions, and sedimentation of droplets forming both as sea spray droplets and background aerosols, as well as aerosol masses within droplets. The turbulent mixing between parcels is explicitly taken into account. Sea spray generation is determined by a source function depending on the background wind speed assumed in the simulations to be equal to 20 m s−1. The results of simulations obtained by taking into account the effects of LE are compared to those obtained under the assumption that the vertical transport of droplets and passive scalars is caused by small-scale turbulent diffusion. Small-scale turbulence diffusion taken alone leads to an unrealistic MBL structure. Nonlocal mixing of the MBL caused by LE leads to the formation of a well-mixed MBL with a vertical structure close to the observed one. LE lead to an increase in the sensible and latent heat surface fluxes by 50%–100% and transport a significant amount of large spray droplets upward. Microphysical processes lead to formation of spray-induced drizzling clouds with cloud base near the 200-m level.

Trajectory planning for mini unmanned helicopter in obstacle and windy environments

2018 ◽  
Vol 90 (5) ◽  
pp. 806-814
Author(s):  
Jinwu Xiang ◽  
Tong Shen ◽  
Daochun Li
Keyword(s):  
Boundary Layer ◽  
Trajectory Planning ◽  
Wind Field ◽  
High Speed ◽  
Pseudospectral Method ◽  
Strong Wind ◽  
Unmanned Helicopter ◽  
Wind Fields ◽  
Content Type ◽  
Flight Dynamics Model

Purpose Obstacle and wind field are common environmental factors for mini unmanned helicopter (MUH) flight. This paper aims to develop a trajectory planning approach guiding MUH to avoid static and dynamic obstacles and to fly in steady uniform or boundary-layer wind field. Design/methodology/approach An optimal control model including a nonlinear flight dynamics model and a cubic obstacle model is established for MUH trajectory planning. Radau pseudospectral method is used to generate the optimal trajectory. Findings The approach can plan reasonable obstacle-avoiding trajectories in obstacle and windy environments. The simulation results show that high-speed wind fields increase the flight time and fluctuation of control inputs. If boundary-layer wind field exists, the trajectory deforms significantly and gets closer to the ground to escape from the strong wind. Originality/value The key innovations in this paper include a cubic obstacle model which is straightforward and practical for trajectory planning and MUH trajectory planning in steady uniform wind field and boundary-layer wind field. This study provides an efficient solution to the trajectory planning for MUH in obstacle and windy environments.

A Sensitivity Research of Numerical Simulation about Winter Sea-Land Breeze

2013 ◽  
Vol 380-384 ◽  
pp. 1800-1803
Author(s):  
Xiao Lan Tang ◽  
Shui Yuan Cheng
Keyword(s):  
Numerical Simulation ◽  
Wind Field ◽  
Wrf Model ◽  
Horizontal Resolution ◽  
Land Breeze ◽  
Threshold Values ◽  
Tropical Island ◽  
Wind Field Simulation ◽  
Field Simulation ◽  
The Impact

Using the WRF model and NCEP data, a typical winter sea-land breeze progress in China tropical island was simulated, analyzing the impact of wind field simulation with the horizontal resolution, analog range, nesting level, and analog time. The results showed: the simulate effects of the WRF model could not always keep step with the increase of horizontal resolution. Obviously there was a threshold for the model horizontal resolution. By the same token, analog range, nesting level, and analog time have its threshold. The accuracy of the simulation reduced when the threshold values were exceeded.

scholarly journals Instabilities in oblique shock wave/laminar boundary-layer interactions

2016 ◽  
Vol 789 ◽  
pp. 1-35 ◽  
Author(s):  
F. Guiho ◽  
F. Alizard ◽  
J.-Ch. Robinet
Keyword(s):  
Boundary Layer ◽  
Shock Wave ◽  
Shear Layer ◽  
Laminar Boundary Layer ◽  
Oblique Shock ◽  
Oblique Shock Wave ◽  
Two Dimensional ◽  
Linear Framework ◽  
Displacement Thickness ◽  
The Impact

The interaction of an oblique shock wave and a laminar boundary layer developing over a flat plate is investigated by means of numerical simulation and global linear-stability analysis. Under the selected flow conditions (free-stream Mach numbers, Reynolds numbers and shock-wave angles), the incoming boundary layer undergoes separation due to the adverse pressure gradient. For a wide range of flow parameters, the oblique shock wave/boundary-layer interaction (OSWBLI) is seen to be globally stable. We show that the onset of two-dimensional large-scale structures is generated by selective noise amplification that is described for each frequency, in a linear framework, by wave-packet trains composed of several global modes. A detailed analysis of both the eigenspectrum and eigenfunctions gives some insight into the relationship between spatial scales (shape and localization) and frequencies. In particular, OSWBLI exhibits a universal behaviour. The lowest frequencies correspond to structures mainly located near the separated shock that emit radiation in the form of Mach waves and are scaled by the interaction length. The medium frequencies are associated with structures mainly localized in the shear layer and are scaled by the displacement thickness at the impact. The linear process by which OSWBLI selects frequencies is analysed by means of the global resolvent. It shows that unsteadiness are mainly associated with instabilities arising from the shear layer. For the lower frequency range, there is no particular selectivity in a linear framework. Two-dimensional numerical simulations show that the linear behaviour is modified for moderate forcing amplitudes by nonlinear mechanisms leading to a significant amplification of low frequencies. Finally, based on the present results, we draw some hypotheses concerning the onset of unsteadiness observed in shock wave/turbulent boundary-layer interactions.

Impact of Elevated Kevin-Helmholtz Billows on the Atmospheric Boundary Layer

2021 ◽  
Author(s):  
Qingfang Jiang
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Shear Layer ◽  
Exponential Growth ◽  
Three Dimensional ◽  
Large Eddy Simulations ◽  
Two Dimensional ◽  
Large Eddy ◽  
Saturation Stage ◽  
The Impact

AbstractThe impact of Kelvin-Helmholtz billows (KHBs) in an elevated shear layer (ESL) on the underlying atmospheric boundary layer (BL) is examined utilizing a group of large-eddy simulations. In these simulations, KHBs develop in the ESL and experience exponential growth, saturation, and exponential decay stages. In response, strong wavy motion occurs in the BL, inducing rotor circulations near the surface when the BL is stable. During the saturation stage, secondary instability develops in the ESL and the wavy BL almost simultaneously, followed by the breakdown of the quasi-two-dimensional KH billows and BL waves into three-dimensional turbulence. Consequently, during and after a KH event, the underlying BL becomes more turbulent with its depth increased and stratification weakened substantially, suggestive of significant lasting impact of elevated KH billows on the atmospheric BL. The eventual impact of KHBs on the BL is found to be sensitive to both the ESL and BL characteristics.

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