Computational aero-acoustic modelling of external rear-view mirrors on a mid-sized Sedan
TL;DR: In this paper, the authors analyzed the contribution of external rear-view mirrors to the total drag force and the overall sound pressure level at the A, B and C pillars, while optimising the external rearview mirror design accordingly.
Abstract: Ever-rising fuel costs necessitate design of fuel-efficient vehicles. Consequently, modern vehicle manufacturers are focused on designing low aerodynamic drag vehicles which would in-turn reduce the fuel consumption. This study analyses the contribution of external rear-view mirrors to the total drag force and the overall sound pressure level at the A, B and C pillars, while optimising the external rear-view mirror design accordingly. Solid Works renditions of external rear-view mirror models mounted on a reference luxury sedan were analysed using a commercially available computational fluid dynamic package ANSYS FLUENT. A different approach was followed to carry out the empirical flow visualisation and predict sound pressure levels. The aerodynamic characterisation of the vehicle was done utilising the widely used shear stress transport turbulence model, while the analysis of wind noise and the contributing vortices employed a large eddy simulation. This approach significantly reduced computational time ...
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TL;DR: In this article, the shape of a bionic shark fin was applied to the shell of a side view mirror to reduce the negative pressure area and reduce the turbulence intensity at the rear of the mirror.
Abstract: The LES (Large Eddy Simulation) model based on different subgrid-scale models was used to calculate the aerodynamic noise of the side view mirror. The simulation result of Algebraic Wall-Modeled LES Model (WMLES) in LES was proved to be more accurate through the wind tunnel test. In order to explore the noise reduction mechanism of bionic shark fin, the shape of shark fin was studied and applied to the shell of side view mirror. The simulation results indicated that the bionic shark fin structure could effectively comb the streamline of the side view mirror surface and reduce the negative pressure area. The turbulence intensity at the rear of the side view mirror was reduced, which was beneficial to reduce the aerodynamic noise of the side view mirror on the front side window area. The maximum noise reduction could reach 7.3 dB.
6 citations
TL;DR: In this article, a bionic hemispherical convex structure in the A pillar-rear view mirror regions according to actual requirements was adopted, and impacts of the bionic structure on aerodynamic characteristics and noises in the region were studied.
Abstract: The paper adopted a bionic hemispherical convex structure in the A pillar-rear view mirror regions according to actual requirements. Furthermore, impacts of the bionic structure on aerodynamic characteristics and noises in the region were studied. Friction resistance of airflows was greatly reduced, fluctuations and pulsation pressures of flow fields were also reduced, and characteristics of flow fields and sound fields were improved. The computational results were finally verified by the experimental test. Firstly, the aerodynamic lift force coefficient and drag force coefficient of the bionic model were computed, and they were obviously lower than those of the original model. The adhesive force between tires and ground during vehicle running was increased, and the danger degree of “waving” of high-speed vehicle running was weakened. In this way, stability of vehicle running could be improved. Secondly, flow fields of the bionic model were computed. Compared with the original model, an obvious vortex was behind the original model, while no vortexes were behind the bionic model. Therefore, convex structures of the bionic model had obvious impacts on flow fields behind the rear view mirror. Airflow separation situations were obvious improved at wheels, windshield and rear side windows of the bionic model. Due to blocking of convex structures of the A pillar and rear view mirror in the bionic model, airflows was hindered and obvious dragging phenomena were formed. Therefore, flow fields in the side window regions could be improved greatly. In addition, the flow field scope under the rear view mirror in the bionic model was also decreased. Ringed vortex structures appeared behind the rear view mirror in the bionic model. The ringed vortex structures were closely interlaced and then extended together backwards. Vortexes behind the rear view mirror in the original model were chaotic, where most of them were attached on the surface of side windows. In the original model, turbulent flows with certain strength were on the right upper corner of the side window region. In the bionic model, no turbulent flows were in the same regions. This result indicated that through using the bionic convex structures, airflows flowing through side windows could be combed and could move backwards towards upper and lower edges of the side windows. It could be predicted that pulsation pressures on the side window surface would surely decrease. Therefore, aerodynamic noises caused by pulsation pressures in side window regions would also be improved correspondingly. Especially in regions behind A pillar-rear view mirrors, the maximum noise reduction amplitude reached about 20 dB.
3 citations
Cites background from "Computational aero-acoustic modelli..."
...In reference [18], this study analyses the contribution of external rear-view mirrors to the total drag force and the overall sound pressure level at A, B and C pillars, while optimizing the external rear-view mirror design accordingly....
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References
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TL;DR: In this paper, two new two-equation eddy-viscosity turbulence models are presented, which combine different elements of existing models that are considered superior to their alternatives.
Abstract: Two new two-equation eddy-viscosity turbulence models will be presented. They combine different elements of existing models that are considered superior to their alternatives. The first model, referred to as the baseline (BSL) model, utilizes the original k-ω model of Wilcox in the inner region of the boundary layer and switches to the standard k-e model in the outer region and in free shear flows. It has a performance similar to the Wilcox model, but avoids that model's strong freestream sensitivity
15,459 citations
TL;DR: In this article, an extended period numerical integration of a baroclinic primitive equation model has been made for the simulation and the study of the dynamics of the atmosphere's general circulation, and the solution corresponding to external gravitational propagation is filtered by requiring the vertically integrated divergence to vanish identically.
Abstract: An extended period numerical integration of a baroclinic primitive equation model has been made for the simulation and the study of the dynamics of the atmosphere's general circulation. The solution corresponding to external gravitational propagation is filtered by requiring the vertically integrated divergence to vanish identically. The vertical structure permits as dependent variables the horizontal wind at two internal levels and a single temperature, with the static stability entering as a parameter. The incoming radiation is a function of latitude only corresponding to the annual mean, and the outgoing radiation is taken to be a function of the local temperature. With the requirement for thermal equilibrium, the domain mean temperature is specified as a parameter. The role of condensation is taken into account only as it effectively reduces the static stability. All other external sources and sinks of heat are assumed to balance each other locally, and are thus omitted. The kinematics are th...
12,952 citations
08 May 1969-Philosophical transactions - Royal Society. Mathematical, physical and engineering sciences
TL;DR: In this article, sound generation by turbulence and surfaces in arbitrary motion is discussed, and sound and multipole fields and governing equations are discussed. But sound generation is not discussed in this paper.
Abstract: Monograph on sound generation by turbulence and surfaces in arbitrary motion, discussing sound and multipole fields and governing equations
3,121 citations
"Computational aero-acoustic modelli..." refers methods in this paper
...In equation (18), ui = fluid velocity component in the xi direction, un = fluid velocity component normal to surface f = 0, v x i i = surface velocitycomponent in the direction, vn = surface velocitycomponent normal to thesurface, δ (f) = Dirac delta function, H f ( ) = Heaviside function, a0 = speed of sound in the far-field, ′ p = far-field sound pressure and f = 0 refers to the FW-H surface which is used to embed the external flow problem ( ) f > 0 and facilitates the use of the free-space Green function to obtain the solution....
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Book•
01 Jan 1995
TL;DR: A Thomas's algorithm for the solution of a tridiagonal system of Equations is described in this paper, as well as a detailed discussion of the future of Computational Fluid Dynamics.
Abstract: Part I*Basic Thoughts and Equations 1 Philosophy of Computational Fluid Dynamics 2 The Governing Equations of Fluid Dynamics Their Derivation, A Discussion of Their Physical Meaning, and A Presentation of Forms Particularly Suitable to CFD 3 Mathematical Behavior of Partial Differential Equations The Impact on Computational Fluid Dynamics Part II*Basics of the Numerics 4 Basic Aspects of Discretization 5 Grids and Meshes, With Appropriate Transformations 6 Some Simple CFD Techniques A Beginning Part III*Some Applications 7 Numerical Solutions of Quasi-One-Dimensional Nozzle Flows 8 Numerical Solution of A Two-Dimensional Supersonic Flow Prandtl-Meyer Expansion Wave 9 Incompressible Couette Flow Numerical Solution by Means of an Implicit Method and the Pressure Correction Method 10 Incompressible, Inviscid Slow Over a Circular Cylinder Solution by the Technique Relaxation Part IV*Other Topics 11 Some Advanced Topics in Modern CFD A Discussion 12 The Future of Computational Fluid Dynamics Appendixes A Thomas's Algorithm for the Solution of A Tridiagonal System of Equations References
1,738 citations
Book•
05 Feb 1987
TL;DR: In this paper, the authors present an introduction to automobile aerodynamics, including aerodynamic drag of cars and light vans, and numerical methods for computation of flow around road vehicles, and wind tunnels for automobile aerodynamic testing.
Abstract: Contents: Introduction to automobile aerodynamics. Some fundamentals of fluid mechanics. Performance of cars and light vans. Aerodynamic drag of passenger cars. Driving stability in side winds. Operation, safety and comfort. High performance vehicles. Commercial vehicles. Engine cooling systems. Heating, ventilation and air conditioning of motor vehicles. Wind tunnels for automobile aerodynamics. Measurement and test techniques. Numerical methods for computation of flow around road vehicles.
802 citations