Design and aerodynamic analysis of an Automotive Adaptive Rear Diffuser

Traditional vehicles are designed to bring out the best performance, good fuel economy, fewer emissions, and good high-speed stability. In this process of designing a vehicle, the underbody geometry of a car plays a vital role and is often neglected because of its complicated design bits. Though the presence of uneven surfaces causes the layers of air to separate resulting in generating turbulence. This report is about designing an active rear diffuser of a car. The rear diffuser is an aerodynamic device that is installed in the end part of the underbody of a car. Diffuser now a day is quite a common aerodynamic device that is used in performance cars. The main moto of attaching a diffuser is to reduce the wake produced behind the car and help the streamlines to converge better. The prime focus of this study is to design an active rear diffuser that will not only help in providing great high-speed stability and aerodynamic efficiency but will also use the aerodynamic forces adversely to help the car stop faster and on its track. This is made possible first by understanding the effects of diffuser angle on the aerodynamic forces acting on the car. Further, to actually transform the computational values into a working model, an electronic circuit is designed which mimics the exact movement of the diffuser according to the speed and other driving conditions. Keywords: Adaptive, diffuser, automobile, aerodynamic, aerodynamic Drag, aerodynamic Lift

3-D Computational Study of a Diffuser Augmented Micro Wind Turbine

The present study focuses on the design optimization of a 3D DAMWT (Diffuser Augmented Micro Wind Turbine geometry). DAMWTS are compact devices with a swept area of only few square meters and energy production capacity of a few kilowatts. Their small size makes it convenient for domestic power generation. The box-shaped shroud makes it possible to stack multiple DAMWTS in an array configuration, thereby multiplying power output. 3-D CFD simulations were carried out using the k-ω SST turbulence model to compare the performance characteristics of different turbine geometries with a square inlet. With a constant shroud diffuser angle of 12 degrees as obtained in a previous study, the shroud nozzle angle and curvature were varied to obtain the maximum velocity factor and minimize flow stagnation at the inlet. Best performance was obtained with a nozzle angle of approximately 27 degrees and semi-concave curvature, with a velocity factor of 1.2. Further increase in nozzle angle resulted in a decline in performance and an increased flow stagnation. To analyze the influence of stacking on flow characteristics, a computational study of two DAMWTS placed horizontally next to each other was carried out. An investigation of the effectiveness of Vortex Generators in inhibiting flow stagnation at the inlet was also conducted.

Quantitative characterization of volume of cavities in hydrodynamic cavitation device using computational fluid dynamics

Hydrodynamic cavitation has been extensively studied for its potential to remove emerging pollutants. Despite the advance of the experimental studies involving this phenomenon, computational studies that evaluate the influence of the geometry of the cavitation devices on the flow parameters are still necessary. The purpose of this article was to evaluate the influence of the change in the geometry of a Venturi device on the volume of cavities formed in its divergent section using Computational Fluid Dynamics (CFD). The geometric parameters modified in the Venturi were: the diffuser angle and the relation between the height and the width of the throat (h/w). The volume of cavities is an important parameter because it influences the cavitation intensity. A cavitational bench system was constructed in order to obtain input data for simulation. The results showed that the increase in the diffuser angle from 6.5° to 18.5° gradually reduced the volume of cavities from 93 mm3 to 10 mm3. Between the relations h/w = 0.05 and h/w = 0.45 was observed the formation of cavities between 106 mm3 and 77 mm3, however between h/w = 0.45 and h/w = 1.0 there was the formation of 213 mm3. Therefore, Venturi’s with diffuser angle less than 6.5º and relation h/w greater than 0.45 produce greater volume of cavities. The greater volume of cavities will not necessarily produce greater cavitational intensity, since cavitation clouds can be formed and reduce the implosion intensity of the cavitation bubbles.

Flat diffuser: steady state flow of a viscous incompressible fluid

The article analyzes the evolution of the main single-mode stationary flow of a viscous incompressible fluid in a flat diffuser (with a constant sign in the flow velocity depending on the aperture angle of the diffuser) in the classical formulation of the Jeffrey — Hamel problem. Depending on the determining parameters (the diffuser angle and the Reynolds number), a complete solution of the problem is given. The transition of main single-mode flow at a fixed angle of the diffuser to the multimode modes (where the velocity of flow changes sign depending on the angle of the diffuser) when the Reynolds number has been changed is shown. It is found that starting from a certain critical value of the Reynolds number, the existence of a stationary single-mode flow is impossible. The corresponding bifurcation diagram is constructed and the dependence of this critical value vs. the aperture angle of diffuser is found. The possibility of realization of both single-mode and multimode flows at the same Reynolds number is shown. The parameters of the second and third bifurcation domains are also calculated.

Experimental and numerical investigations of the vehicle aerodynamic drag with single-channel rear diffuser

The main purpose of this paper is to reveal the drag reduction mechanism of single-channel rear diffuser on the vehicle aerodynamic drag and to obtain the relationship between the structure parameters of rear diffuser and the vehicle aerodynamic drag. The influence of the single-channel rear diffuser on the aerodynamic drag is studied using the Reynolds-averaged method with the 25° slant Ahmed model. The accuracy of the numerical method is validated by means of a wind tunnel test. The aerodynamic performance of the Ahmed model with different vertical diffuser angles, lateral diffuser angles, and channel widths is discussed. The results demonstrate that the vortex location will be influenced by the vertical diffuser angle, and with the vortex core approaching to the model, the aerodynamic drag will increase. The aerodynamic drag reaches the minimum value with a vertical diffuser angle of 10.46°. Moreover, the aerodynamic drag decreases with increasing channel width. Finally, the aerodynamic drag can be reduced by 5.3%, when the vertical diffuser angle, lateral diffuser angle, and channel width are 10.46°, 0°, and 351 mm, respectively.

ANALISIS UNJUK KERJA VENTURI VAKUM DENGAN VARIASI DIMENSI DAN VISKOSITAS FLUIDA

In the venturi vacuum, to produce a vacuum condition, a liquid fluid flow is required which is driven by a centrifugal pump through the venturi passage. The amount of vacuum pressure generated by venturi is influenced by the increase of flow velocity due to the diminution of the cross-section which follow Bernoulli principle. The flow velocity on the channel is influenced by the discharge generated by the pump following the continuity law. In addition to speed, channel input pressure is also a variable that affects venturi vacuum pressure. Performance of a setrifugal pump in the form of flow and pressure discharge greatly affect venturi vacuum performance, so that the variables affecting the performance of a setrifugal pump such as fluid viscosity, will also affect the venturi vacuum performance. Therefore, it is necessary to evaluate the effect of viscosity and venturi dimension on vacuum pressure and discharge into the main objective of this study so that the variables can improve the venturi vacuum pump performance. In this study liquid fluid with three variations of viscosity flowed through three different venturi dimension variations. Then measured parameters that occur, such as fluid flow fluid flow, fluid pressure fluid and vacuum pressure that occurs in the tube. From this study obtained, at the angle of diffuser 5o the lowest vacuum pressure of - 66.75 cmHg occurs in water fluid with viscosity of 17 centipoise. Similarly, at the angle of the diffuser 6.5o the value of the lowest vacuum pressure is also produced by a water fluid of -68 cmHg which is the lowest value compared to other diffuser angles and other fluid viscosities. While at 8o diffuser angle, the lowest vacuum pressure value is also produced by water fluid of -64.5 cmHg.

Influence of the Groove-Patterned Cooling Tube on the Film Cooling Performance of Gas Turbine

The gas turbine performance significantly depends on the temperature of working fluid. In order to improve the efficiency of gas turbine, it is required to increase turbine inlet temperature. However, the working fluid in high temperature conditions causes thermal stress which could damage turbine blades. One of the methods to require turbine blades by controlling the temperature of working fluid is a film-cooling method. In this study, cooling tubes with various aspect ratios of groove length (L/Lt) with groove diameter of d = 1.2 mm were considered to enhance the film cooling efficiency. In addition, effects of blowing ratios (M) and diffuser angles (δ) of the cooling tube were considered. Numerical investigations were conducted using ANSYS ver. 17.1, and film cooling efficiencies of each case were obtained. Especially, the case with groove length aspect ratio of L/Lt = 0.4 at blowing ratio M = 1.4 and diffuser angle δ = 3.5° showed the highest cooling efficiency of 18% among all model cases.