Rear Shape Research Articles

Effects of Vortex Generators on Aerodynamic Drag Force in the Hatchback Type Car

Aerodynamic drag force is one of the main obstacles on moving a vehicle. This force significantly reduces a vehicle's speed and, as a result, its fuel efficiency. In today’s scenario, fuel efficiency is a prime concern in vehicle design, so a reduction in aerodynamic drag force is highly important. Road vehicles are designed to pass through surrounding air and displace it as efficiently as possible. Due to the rear shape of a car, airflow suddenly separates from the vehicle at a point near the rear windscreen. This flow separation at the rear end of the car is responsible for the drag force, which is the main opposition to the vehicle's forward motion. This drag force is proportional to the square of the velocity of the car and, as a result, increases significantly after certain speeds. To reduce the drag force, the flow separation at the rear end needs to be avoided. In hatch-back type cars, to avoid this separation, a vortex generator (VG) can be used. VG creates the vortex at the rear end of the car, which delays the flow separation and, ultimately, drag is reduced significantly. In this work, the effect of a VG on the pressure distribution, velocity destitution and aerodynamic drag on the hatchback type car, is studied by the numerical simulation. The numerical simulations are carried out using the ANSYS FLUENT® software. The simulation setup is validated with wind tunnel test results.

Flow analysis of rear end body shape of the vehicle for better aerodynamic performance

This paper discusses the aerodynamic flow characteristic of car with various rear shape car body. 80 to 90% of total aerodynamic drag will occurs from base pressure which is created by pressure difference of front and rear side of car. Increasing of pressure difference mainly occurs due to rear end shape of car while it is moving. The proper shape of car, which give less drag and better stability and handling of vehicle by creating streamline flow over the vehicle. For this study, we choose passenger cars with various rear shape such as Hatchback car, Sedan car, Square back car and Fastback car. The experimental work was done in open circuit subsonic wind tunnel with the subscale model 1:10 of all rear shape model at various velocities. The aerodynamic coefficients of drag, lift and pressure (Cd, Cl, and Cp) of car models are plotted to understand the effects of flow condition form the experimental work. The experimental results revels that the sedan car and fast back car are having better aerodynamic performance compare to other car model. And also suggest that researcher will choose better option is hatchback or square back car model for further modification of rear end body to getting better aerodynamic performance.

Analysis of the configuration and the location of thermographic equipment for the inspection in photovoltaic systems

The infrared (IR) thermography is a non-destructive technique (NDT) which is used to carry out maintenance quickly and easily in photovoltaic (PV) systems. IR imaging with thermographic cameras under steady state conditions is a usual method for quality control of PV modules and plants in operation. For the proper IR inspection which determines the severity or the importance of the detected findings, it is necessary to consider different aspects of the configuration and the location of the thermographic equipment which allow reducing measuring errors. This paper considers some elements which contribute to the accurate configuration of the thermographic equipment. The influence of the reflected apparent temperature in outdoor IR inspections is analysed and it is proposed a simple method for obtaining it. Besides, the importance of the emissivity in IR thermography is analysed. For that, the value of the emissivity in PV modules of various types both front and rear shape is determined experimentally. It is also studied the proper location of the thermographic equipment in order to minimize reflections of the sun and the sky. For this objective, it is studied the ideal and minimum height of inspection according to the layout of the PV system. In a particular case, it is also analysed the influence of the horizontal angle of thermographic inspection and the reflected radiation.

Improvement of separator performance with modified pick-off ring and swirler

The swirler and the 1st pick-off ring (POR) of a gas-liquid separator are improved to reduce the pressure drop, ΔPT, in the separator while keeping the flow rate of separated liquid, WST, high. Two swirler designs are presented, i.e. V8 (swirler with eight vanes) and V6 (swirler with six vanes), whose diameters of the hubs supporting the vanes are smaller than that of the normal swirler, N8, and the nose shape of vanes are coned. The swirlers are installed into a one-fifth scale separator with three PORs. The gap width of the 1st POR is reduced to the value of the liquid film thickness in the barrel of the separator and the rear shape of the 1st POR is smoothed. The performance of the downscaled separator with the proposed swirlers and the 1st POR are evaluated under the nominal operating condition of the Hyper BWR and a higher quality condition. As a result, the following conclusions are obtained in the present experimental range: (1) ΔPT in the separator is reduced by 23% using V8, and V8 gives the same WST as N8, confirming that the decrease in the hub diameter and the coned-nose shape of vanes are effective, (2) V6 can realize further reduction of ΔPT (38%) without deteriorating the liquid-separation rate, (3) the reduced gap width of the 1st POR and a tapered shape of the downstream side of the 1st POR are also effective to decrease the pressure drop, i.e. the improved POR decreases ΔPT by 42% and 54% by combining with V8 and V6, respectively, and (4) the improved separators also show good performances in ΔPT and WST at the higher quality condition.

Rear shape in 3 dimensions summarized by principal component analysis is a good predictor of body condition score in Holstein dairy cows

Body condition is an indirect estimation of the level of body reserves, and its variation reflects cumulative variation in energy balance. It interacts with reproductive and health performance, which are important to consider in dairy production but not easy to monitor. The commonly used body condition score (BCS) is time consuming, subjective, and not very sensitive. The aim was therefore to develop and validate a method assessing BCS with 3-dimensional (3D) surfaces of the cow’s rear. A camera captured 3D shapes 2 m from the floor in a weigh station at the milking parlor exit. The BCS was scored by 3 experts on the same day as 3D imaging. Four anatomical landmarks had to be identified manually on each 3D surface to define a space centered on the cow’s rear. A set of 57 3D surfaces from 56 Holstein dairy cows was selected to cover a large BCS range (from 0.5 to 4.75 on a 0 to 5 scale) to calibrate 3D surfaces on BCS. After performing a principal component analysis on this data set, multiple linear regression was fitted on the coordinates of these surfaces in the principal components’ space to assess BCS. The validation was performed on 2 external data sets: one with cows used for calibration, but at a different lactation stage, and one with cows not used for calibration. Additionally, 6 cows were scanned once and their surfaces processed 8 times each for repeatability and then these cows were scanned 8 times each the same day for reproducibility. The selected model showed perfect calibration and a good but weaker validation (root mean square error=0.31 for the data set with cows used for calibration; 0.32 for the data set with cows not used for calibration). Assessing BCS with 3D surfaces was 3 times more repeatable (standard error=0.075 versus 0.210 for BCS) and 2.8 times more reproducible than manually scored BCS (standard error=0.103 versus 0.280 for BCS). The prediction error was similar for both validation data sets, indicating that the method is not less efficient for cows not used for calibration. The major part of reproducibility error incorporates repeatability error. An automation of the anatomical landmarks identification is required, first to allow broadband measures of body condition and second to improve repeatability and consequently reproducibility. Assessing BCS using 3D imaging coupled with principal component analysis appears to be a very promising means of improving precision and feasibility of this trait measurement.

Effect of Car Rear Shape on Pollution Dispersion in Near Wake Region

Dispersion of vehicle exhaust gas is a primary source of air pollution in urban areas. Thus, it has become an important subject in the automotive field. This paper consists of two parts. First, the fastback MIRA model was selected as study object and a standardκ-εtwo-equation turbulence model was used. The simulation results were compared and analyzed with experimental data. The feasibility of the turbulence model and grid strategy was then verified, and the results were used in the next research step. Second, we used propane as tracer gas while ignoring the effect of the vehicle wake field force on this gas. The tracer gas diffusion in the wake flow field was then simulated through fastback, notchback, and square-back MIRA models. This study focuses on analyzing the characteristics of wake field diffusion effects, particularly in the near wake of a vehicle.

Numerical and Experimental Investigations on the Aerodynamic Characteristic of Three Typical Passenger Vehicles

The numerical simulation and wind tunnel experiment were employed to investigate the aerodynamic characteristics of three typical rear shapes: fastback, notchback and squareback. The object was to investigate the sensibility of aerodynamic characteristic to the rear shape, and provide more comprehensive experimental data as a reference to validate the numerical simulation. In the wind tunnel experiments, the aerodynamic six components of the three models with the yaw angles range from -15 and 15 were measured. The realizable k-e model was employed to compute the aerodynamic drag, lift and surface pressure distribution at a zero yaw angle. In order to improve the calculation efficiency and accuracy, a hybrid Tetrahedron-HexahedronPentahedral-Prism mesh strategy was used to discretize the computational domain. The computational results showed a good agreement with the experimental data and the results revealed that different rear shapes would induce very different aerodynamic characteristic, and it was difficult to determine the best shape. For example, the fastback would obtain very low aerodynamic drag, but it would induce positive lift which was not conducive to stability at high speed, and it also would induce bad crosswind stability. In order to reveal the internal connection between the aerodynamic drag and wake vortices, the turbulent kinetic, recirculation length, position of vortex core and velocity profile in the wake were investigated by numerical simulation and PIV experiment.

The Aerodynamic Characteristics of a Microbus

This work is focused on the reduction of the aerodynamic resistance of a microbus. The approach is the three dimensional (3-D) numerical simulation. The RNG k–ε turbulence models are adopted in the computation. Based on the model of SC6350 Chang’an microbus and the improved rear shape, the aerodynamic characteristics of both models at different speeds are studied. Flow maps drawn on the basis of the computed results can offer a reliable method to study the flow field around a microbus. The computed results can give a reference for study of the aerodynamic resistance reduction on a microbus for energy saving. And the results of the optimized shape can provide a theoretical basis for the related research.

Multidisciplinary Shape Optimization of Aerostat Envelopes

an = coefficient for parabolic rear shape a1, a2, b1, b2, c1, c2, d1, d2 = coefficients of cubic splines that parameterize the center portion of the envelope CD = drag coefficient d = envelope diameter l = envelope length n = load per unit length along meridians, i.e., in warp direction n’ = load per unit length along latitude circles, i.e., in weft direction pR = internal overpressure in the aerostat envelope R = radius of curvature of spherical front portion of envelope R1, R2 = radii of curvature and transverse curvature of an inflated structure XD = design vector for shape optimization

Sensory selection in vehicle detection and avoidance

A general paradigm for vehicle detection and avoidance by proper selection of visual and sonar sensors is presented. The most appropriate sensor for detection and navigation of the robot is selected in accordance with the sensor functions and limitations. This strategy is activated when one sensor cannot obtain enough information for navigation of the robot because of sensor limitations. Five types of actions based on stereotyped motion are used for the navigation system: Moving Along Wall, Moving Along, Moving Toward, Tracking Motion and Danger Estimation. The first is sonar based and the rest are vision based actions. Visual detection of the vehicle is based on the locomotion strategy “Sign Pattern based Stereotyped Motion” . The sign pattern of the vehicle is the shadow underneath the vehicle, which is darker than any other parts of the paved road. The robot detects the sign pattern of a vehicle from a distance of more than 30 m and extracts its front or rear shape on 2-D image by video rate processing. Moreover, to make a decision for further action of the robot, a time series information of vehicles on the paved road are provided during tracking process.

Improvement of vehicle aerodynamics by wake control

The rear-end shape of a car is one of the most important parts from the view point of aerodynamics. It governs the aerodynamic characteristics of the car, especially drag and rear lift. However, a rear-end shape like a spoiler often increases drag on recent low-drag cars. In this paper, the relation of rear-end shape to drag and lift is studied by consideration of the wake structure, which is obtained by wind tunnel testing and CFD. Finally, a new rear shape which reduces rear lift without increasing drag and front lift is discussed.

Vortex shedding mechanism from a triangular prism in a subsonic flow

Alternate periodic vortices shed from a triangular prism arranged as either a wedge or a reversed wedge are studied experimentally at a Mach number of 0.377 and at a Reynolds number of 1.73 × 105 (based on the prism height). It is found that the flow around the triangular prism arranged as a wedge (referred to as prism 1) separates at the sharp trailing edges, and the main vortices are generated immediately after the separation. No secondary vortex is generated around prism 1 ; however the flow around the other triangular prism arranged as a reversed wedge (prism 2) separates at the sharp leading edges. The main vortices are not formed immediately after the separation; rather their formation is finished either over or under the trailing edge. In this case, strong secondary vortices on and beneath the trailing edge are generated by the upper and lower main vortices, respectively. The vortices behind prism 1 are weaker than those behind prism 2, but the rate of the vortex shedding process behind prism 1 is higher than that behind prism 2. That is, the weaker the vortices are, the higher the rate of the vortex shedding process (or the Strouhal number) is, and vice versa. The vertical spacing between the loci of the upper and lower main vortices behind prism 1 is wider than that behind prism 2, but the width of the wake behind prism 1 is narrower than that behind prism 2. It is suggested that the Strouhal number for a wedge is sensitive to the front shape (i.e. the wedge angle), but that for a reversed wedge is not sensitive to the rear shape. Finally, the vortex shedding mechanism from a triangular prism arranged as either a wedge or reversed wedge has been proposed. It is concluded that, irrespective of the arrangement, vortex shedding is maintained by the unstable system of three vortices generated in the vortex formation region, but the effect of the downstream oscillating wake on vortex shedding is not critical.