Analysis of hysteresis and phase shifting phenomena in unsteady three-dimensional wakes期刊界 All Journals 搜尽天下杂志传播学术成果专业期刊搜索期刊信息化学术搜索

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Analysis of hysteresis and phase shifting phenomena in unsteady three-dimensional wakes

Authors:	Email author" target="_blank">P?Gilliéron Email author F?Chometon J?Laurent

Institution:	(1) Renault SA, Direction de la Recherche, Service 64260, code API: TCR RUC 405, 1, Avenue du Golf, 78288 Guyancourt Cedex, France;(2) Conservatoire National des Arts et Métiers, 15 rue Marat, 78210 Saint Cyr l'Ecole, France

Abstract:	The aerodynamic characteristics of automobiles are greatly influenced by the unsteady change in the direction of relative airflow. The aim of this paper is to analyse how such a change influences vehicle wake flow patterns. An analysis was conducted on a simplified model capable of reproducing the typical structures encountered under the aerodynamic conditions of an automobile. The results were processed by mapping the steady and unsteady total pressure losses around the model. The findings should enable automobile development engineers inter alia to identify and analyse the physical phenomena that occur when a vehicle is subjected to a sudden gust of side wind.List of symbols B rod - l length of rod B (m) - angle of rod B (degrees) - D disk - P connection point between disk D and rod B - M _o drive motor of disk D - O centre of rotation of disk D - e radius of disk D (m) - angle of disk (degrees) - t moment of time t (s) - _o angle (degrees) at instant of time t=0 - d diameter of model (m) - C centre of rotation of model - x _c abscissa of centre of rotation C of model (m) - M connection point between model and rod B - pi value=3.14159 - incidence of model (degrees) - _M maximum value of incidence (degrees) - _m minimum value of incidence (degrees) - angular amplitude (degrees) - _c critical angle of incidence (degrees) for steady evolutions - $\alpha _{\rm{c}}^$ critical angle of incidence (degrees) for the unsteady evolutions - ̄ mean angle of incidence (degrees) - angle (degrees) of the model such that =+ - pulse (rad s^–1) - T period (s) - f frequency (Hz) - R radius of model in meter (m) - $\vec V_{\rm{o}}$ velocity vector of incident airflow - V _o intensity of velocity vector $\vec V_{\rm{o}}$ (m s^–1) - P _io total pressure associated with upstream airflow velocity $\vec V_{\rm{o}}$ (Pa) - P _i local total pressure (Pa or J m^–3) - density (kg m^–3) - C _x drag coefficient - $C_{P_i }$ total pressure coefficient - (m, n) dimensions of grid: lines m, columns n - x X coordinate of sampling plane (m) - y _j Y coordinate of point of index j for j1,n] - z _k Z coordinate of point of index k for k1,m] - P _i(x,y _j,z _k,(t)) continuous data of unsteady total pressure (Pa) - $P_i^ \left( {x,y_j ,z_k ,\alpha ^* \left( t \right)} \right)$ discrete data of unsteady total pressure (Pa) - N number of tomographic images, from 1 upwards over an oscillation period T - $C_{P_{i\max } }$ maximum value of total pressure coefficients for steady evolutions - $C_{P_{i\max } }^{\, + }$ maximum value of total pressure coefficients for unsteady evolutions and increasing incidences - $C_{P_{i\max } }^{\, - }$ maximum value of total pressure coefficients for unsteady evolutions and decreasing incidences - $\Delta C_{P_{i\max } }^ +$ differential between $C_{P_{i\max } }$ and $C_{P_{i\max } }^{\, + }$ - $\Delta C_{P_{i\max } }^ -$ differential between $C_{P_{i\max } }$ and $C_{P_{i\max } }^{\, - }$ - phase shifting (degrees)

Keywords:	Automobile aerodynamics Drag coefficient Total pressure loss Unsteady airflow Wake structure
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