Recent Advances in Wake Dynamics and Active Drag Reduction of Simple Automotive Bodies

This is a compendium of recent progresses in the development of wake dynamics and active drag reduction of three-dimensional simple automotive models, largely focused on the generic Ahmed body. It covers our new understanding of involved instabilities, predominant frequencies, pressure distribution and unsteady flow structures in the high- (12.5° < f < 30°) and low-drag (f > 30°) bodies and the square-back body (f = 0°), where f is the rear slant angle of the body. Various drag reduction methods and their performances are reviewed, including open- and closed-loop controls along with machine-learning control. The involving drag reduction mechanisms, net saving and efficiencies are discussed. Comments are made for the areas that deserve more attention and future investigation.

Investigation of wheelhouse shapes on the aerodynamic characteristics of a generic car model

As vehicle speed increases, the aerodynamic drag reduction becomes increasingly significant. The aim of this paper is to find out the effects of the wheelhouse shapes on the aerodynamics of an Ahmed body with a 35 slant angle. In this paper, based on the detached-eddy simulation method, the effects of the three classic different wheelhouse on the aerodynamic performance and near wake of the Ahmed body are presented. The mesh resolution and methodology are validated against the published test results. The results show that the front wheelhouse has a significant impact on the aerodynamic performance of the Ahmed body, leading to different aerodynamic drag forces and flow fields. Enlarging the wheelhouse cavity volume could result in a gradual increase in aerodynamic drag coefficients, the ratio of the wheelhouse cavity volume increased by 2.9% and 9.8%, the drag coefficients increased by 2.5% and 4.5% respectively. The increase in aerodynamic drag was primarily caused by flow separation in the large cavity volume wheelhouse.

Large Eddy Simulation with wall functions of Ahmed body

Large Eddy Simulation with Wall Function (WFLES) is known to be a cheap alternative to classical LES methods for simulation of flow where large and complex computational meshes are typically required. This makes it attractive for engineering applications. However experience of applying such methods to complex turbulent flows with flow separation and reattachment is still little-known in literature. In this work WFLES of flow around simplified car body with slant angle equal to 25 degrees and ReL = 2.8 · 106 is carried out on Octree mesh to demonstrate the capabilities and limitations of the method in such type of the flow. The results on a series of meshes show that even though the general flow topology is well captured, the critical part of the flow on the slant is hardly predicted even on 100 mln mesh. It is concluded that the prediction of separation above the slant requires significant mesh refinement even in the frame of WFLES.

External aerodynamic investigation over Ahmed body for optimal topology selection between upper and under bodywork using ANN approach

Aerodynamic improvements primarily result in decreased fuel usage and carbon dioxide emissions into the atmosphere. Numerous governments support ongoing aerodynamics development initiatives as a means of addressing the energy problem and reducing air pollution, Ahmed body investigation helps research to investigate versatile approaches and flexibility of design. This study is carried over a generic design of Ahmed body model. We attempted a passive arrangement system to reduce drag coefficient with a correlation of cases such as in primary objective varying parameter of slant angle from 20∘ to 30∘ proposed to monitor the behavior of drag coefficient. Once we finalized the optimum slant angle, which gives a lower drag coefficient, the next proposed configuration is to vary passive arrangement between lower and upper blend length to see the deflection of the boundary layer in correlation with the drag coefficient. The final topology is selected, which gives the lowest drag coefficient. The post-process correlation study was proposed by using an artificial neural network (ANN) scheme. The ANN model is developed between an achieved set of data from CFD investigation, ANN model indicates a strong correlation between the varying percentage of blend angle and increment percentage of the drag coefficient.

An Effective Slant Detection and Correction Method Based on the Tilted Rectangle Method for Telugu Manuscript Terms

This paper proposes an efficient method called tilted rectangle (TR) for detecting and correcting of slant angle of the manuscript Telugu words (MTW). Telugu language is one of India's common languages spoken by over 80 million individuals. The complex characters are attached with some extra marks known as “maatras” and “vatthus,” and it is challenging to detect slant angle. The proposed TR method initially performs preprocessing and identifies a connected component within the given Telugu manuscript word. Then, it estimates the slant angle of each connected component by deriving connected slant lines on the boundary of each connected component. After this process, the proposed TR method estimates the entire word's overall slant angle from the average of estimated slant angle and height of all connected components. The correction of the word's slant angle is done in the reverse direction by applying a simple shear transformation. With 1000 manuscript records of three different kinds, the algorithm is tested. Experimental findings indicate the efficacy of the approach proposed.

Experimental Study of the Skin-Friction Topology Around the Ahmed Body in Cross-Wind Conditions

In this study, skin friction around a ½-scale Ahmed body was measured experimentally at a Reynolds number of Re = 2×105. The slant angle of the Ahmed body was 25° and the yaw angles ranged from 0° to 8°. This study focused on the flow structure on the slant surface under different cross-wind conditions. A force balance system was applied to measure the aerodynamic drag of the model. The global skin-friction topology was measured by applying a luminescent oil layer with a sub-grid data processing algorithm. The method used to measure the skin friction was conducted for the first time on the Ahmed body. The results indicated that the technique is highly capable of extracting the skin-friction topology. For a yaw angle below 3°, the flow on the slant surface was not significantly affected by the cross-wind condition and the drag of the model was nearly constant. However, at yaw angles above 3°, the flow on the slant surface was highly affected by the roof longitudinal vortexes on the windward side, leading to a dramatic increase in the drag of the model. High consistency in the drag and skin-friction fields was observed. The detailed skin-friction structure at different yaw angles will be discussed in this study.

Method of assessing the reduction of solar heat on window surface shaded by continuous vertically slanted shading devices

The research discusses calibration of the method used to calculate solar heat transfer through shaded windows with continuous vertical slanted shading devices (below is abbreviated as "vertical slanted fins") with any slant angle Θ through a radiation reduction coefficient - Kbt. In order to evaluate the reduction of solar heat on window surface shaded by shading devices, a designated coefficient β of solar heat gain reduction through glazed windows should be established. It is the ratio of the transmitted amount of solar heat (including direct and diffuse radiation) through windows with shading device QK to those without solar shading device QKo. The study also introduces two in-house software programs. These programs help calculating solar heat gain and coefficient β for vertically slanted fins with any slant angle θ for 16 window orientations. The results of this study will be applied to the implementation of the Vietnamese national code QCVN 09:2017/BXD towards energy efficiency in buildings.

Mitigating the Costs of Spatial Transformations With a Situation Awareness Augmented Reality Display: Assistance for the Joint Terminal Attack Controller 3-17

Objective Evaluate and model the advantage of a situation awareness (SA) supported by an augmented reality (AR) display for the ground-based joint terminal attack Controller (JTAC), in judging and describing the spatial relations between objects in a hostile zone. Background The accurate world-referenced description of relative locations of surface objects, when viewed from an oblique slant angle (aircraft, observation post) is hindered by (1) the compression of the visual scene, amplified at a lower slang angle, (2) the need for mental rotation, when viewed from a non-northerly orientation. Approach Participants viewed a virtual reality (VR)-simulated four-object scene from either of two slant angles, at each of four compass orientations, either unaided, or aided by an AR head-mounted display (AR-HMD), depicting the scene from a top-down (avoiding compression) and north-up (avoiding mental rotation) perspective. They described the geographical layout of four objects within the display. Results Compared with the control condition, that condition supported by the north-up SA display shortened the description time, particularly on non-northerly orientations (9 s, 30% benefit), and improved the accuracy of description, particularly for the more compressed scene (lower slant angle), as fit by a simple computational model. Conclusion The SA display provides large, significant benefits to this critical phase of ground-air communications in managing an attack—as predicted by the task analysis of the JTAC. Application Results impact the design of the AR-HMD to support combat ground-air communications and illustrate the magnitude by which basic cognitive principles “scale up” to realistically simulated real-world tasks such as search and rescue.