Passive drag reduction of square back road vehicles

Bluff body vehicles such as trucks and buses do not have a streamlined shapes and hence have high drag which can be reduced to make great savings in operational cost. While rectangular flaps have been widely studied as both passive add-ons and in active drag reducing systems for bluff bodies, changing the basic geometry of the flap has not been explored in literature. In this work, a baseline drag value is obtained for a simplified MAN TGX series truck in a CFD software, and the drag reduction of a proposed elliptically shaped flap is compared to aerodynamically equivalent rectangular flaps. The optimal mounting angle for both flaps is found to be 501. A parametric study of changing the ellipse semi-major axis is carried out to find the optimal length for drag reduction. A maximum drag reduction of 11.1% is achieved using an elliptical flap with 0.12 m semi-major axis; compared to 6.37% for a length equivalent rectangular flap, and 6.84% for a surface area equivalent rectangular flap. Results of the pressure distribution and velocity flow behind the rear of the truck are also given and analyzed

Comparison of high-order accurate schemes for solving the nonlinear viscous burgers equation

In this paper, a comparison between higher order schemes has been performed in terms of numerical accuracy. Four finite difference schemes, the explicit fourth-order compact Pade scheme, the implicit fourth-order Pade scheme, flowfield dependent variation (FDV) method and high order compact flowfie ld dependent variation (HOC-FDV) scheme are tes ted. The FDV scheme is used for time disc retization and the fourth-order compact Pade scheme is used for spatial derivatives. The solution procedures consist of a number of tri-diagonal matrix operations and produce an efficient solver. The comparisons are performed using one dimensional nonlinear viscous Burgers equation to demonstrate the accuracy and the convergence characteristics of the high-resolution schemes. The numerical results show that HOC-FDV is highly accurate in comparison with analytical and with other higher order schemes

Interference Analysis for Vehicle-to-Vehicle Communications at 28 GHz

High capacity and ultra-reliable vehicular communication are going to be important aspects of beyond 5G communication networks. However, the vehicular communication problem becomes complex at a large scale when vehicles are roaming on the road, while simultaneously communicating with each other. Moreover, at higher frequencies (like 28 GHz), the dynamics of vehicular communication completely shift towards unpredictability and low-reliability. These factors may result in high packet error and a large amount of interference, resulting in regular disruptions in communications. A thorough understanding of performance variations is the key to moving towards the next generation of vehicular networks. With this intent, this article aims to provide a comprehensive interference analysis, wherein the closed-form expressions of packet error probability (PEP) and ergodic capacity are derived. Using the expression of the PEP, diversity analysis is provided which unveils the impact of channel nonlinearities on the performance of interference-constrained vehicular networks. The insights provided here are expected to pave the way for reliable and high capacity vehicular communication networks

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Stability and takeoff ground roll issues of hybrid buoyant aircraft

Abstract. In the field of aviation, it is well known that a vehicle’s stability and takeoff flight segment are critical issues for a flight vehicle design. These problems become more critical for a hybrid buoyant aircraft which is concealed as an airship with huge volume of hull as compared with fuselage of a conventional aircraft. In the present work, these issues are discussed for a case of generic model of hybrid airship and of a prototype model of a hybrid aircraft. Special emphasis is given for future sizing of empennages of IWHA-14, a hybrid buoyant aircraft concept proposed for Malaysian inter-island transportation. Effect of gondola position on rotation angle for takeoff ground roll was analyzed and it was found that such configurations can meet the laid down requirement of minimum roll angle

Experimental investigation of wing tip vortex

Particle image velocimetery was used in a low-speed wind tunnel to investigate and characterize wing tip vortex structures. A rectangular wing of a SWIM model was used as a vortex generator in two different configurations, (i) plain wing and (ii) flapped wing with trailing edge flap extended at 20 degrees. Vortex flow quantities and their dependence on angle of attack at a chord base Reynolds Number of 32.8x103 and 43.8x103 were evaluated. Assessment of measured data reveals that the peak values of tangential velocities, vortex strength and vorticities are directly proportional to the angle of attack. The vortex core radius value grows slowly as the angle of attack is increased. Both plain and flapped configurations showed similar trends. The peak tangential velocities and circulation distribution doubled when the flapped configuration was used instead of the plain wing

Yawing force of electric trimmers of a hybrid buoyant aerial vehicle

All buoyant and hybrid buoyant aerial vehicles have directional stability issues at low speed. Electric trimmers are one of the potential solutions for controlling the yaw motion of such vehicles in which partial lift is obtained from the wings. However, available propeller disk area of such trimmers is limited due to small surface area of the vertical tail. In the present work, maximum input power required by thin electric propellers with different pitch values are compared to obtain an optimised value of pitch for propeller selection. Analytical as well as computational techniques are employed to evaluate the moment generated by tangential thrust produced by a ducted propeller. Motocalc® software under predicts the thrust value when compared with the computational results under the same flow conditions. The estimated yaw force produced by the propeller is quite significant and it can also be used for creating differential thrust using twin electric motors

Wind tunnel testing of hybrid buoyant aerial vehicle

Purpose – Realistic data bank of aerodynamic and stability derivatives is still missing for hybrid buoyant aerial vehicles. Such vehicles take-off and land similar to an aircraft with their partial weight balanced by the aerostatic lift. The purpose of this paper is to use wind tunnel testing for a better understanding of the aerodynamic and static stability behavior of such vehicles. Design/methodology/approach – The effect of wing on the aerodynamic and static stability characteristics of a clean configuration hybrid buoyant is analyzed. The free stream velocity is 20 m/s, and ranges of angle of attack and side slip angle are from 8° to 12° and 16°, respectively. Data are corrected to account for the effect of strut interference and zero load condition. The maximum blockage of the model with respect to the cross-section area of the test section is about 2.7 per cent. Findings – A hybrid model manufactured by using wood and metal is an optimum solution with less number of parts. The vehicle is statically, longitudinally and directionally stable. Wings designed to fulfill the partial requirement of lift contribute significantly to counter the huge moment generated by the voluminous hull for centre of gravity location ahead of the leading edge of the wing. Research limitations/implications – There are number of manufacturing constraints for scaling down a model of a hybrid buoyant aerial vehicle configuration. Specially, the thickness of the wing limits the testing envelop of angle of attack and free stream velocity. Practical implications – The data presented here are a preliminary guide for further work on larger size models. The data may also be used to build and perform flight tests on small full-scale instrumented models and to obtain flight dynamics data. Originality/value – The estimated aerodynamic and stability derivatives and slopes can be utilized in future for multidisciplinary design

Impact of a Reverse Delta Type Add-on Device on the Flap-tip Vortex of a Wing

The effect of interactions of vortices produced by an outboard flap-tip of a half-span wing (NACA 23012 in landing configuration) and a slender reverse delta type add-on device, placed in the proximity of the outboard flap-tip, on the upper surface of the half-span wing is investigated using Particle Image Velocimetry in a closed loop low speed wind tunnel. Specifically the characteristics of the vortex interactions generated downstream in planes perpendicular to the free stream direction and their dependence on angles of attack at a chord-based Reynolds number of Rec=2.75×105 have been determined. It was found that the add-on device significantly reduces the tangential velocity magnitude and enlarges the vortex core of the resultant vortex by up to 36%. The aerodynamic performance of the half-span wing model was marginally affected by the use of a reverse delta type add-on device. The reduction in lift coefficient is 3.8% and the increase in drag coefficient is 14.9%