آیرودینامیک

This research delves into the practical implications of the effect of exhaust gases on the wake region of an Audi car, which includes vortices and separated flowing from its surface. The findings could potentially inform future vehicle design and performance strategies. The car model's rear configuration is akin to the standard DrivAer Estateback car, which the Aerodynamics Institute of the Technical University of Munich has modeled. The SST k-ω turbulence model is selected for simulation using computational fluid dynamics, considering the problem's nature and the flow stability analysis. To validate the solution method, the numerical results obtained from flow simulation at a Reynolds number of 4.87×106 around the standard model are compared with the experimental results obtained from the wind tunnel. After validating the solution method, it was determined in the initial investigation that at the given Reynolds number, the drag coefficient of the Audi car with an exhaust system is 1.15 % lower than the drag coefficient of the car without an exhaust system. Furthermore, the effects of increasing the vehicle speed, the angle of the exhaust pipe outlet, and finally, the presence of an exhaust on one side of it on the value of the drag coefficient are examined.

In this research, one of the widely used control systems of tailless aircraft, named Crow Flap, has been simulated by numerical method and the appropriate opening direction of this system has been investigated. By creating a differential drag on both sides of the aircraft, this system creates the necessary yawing moment and directional control. This system consists of two moving surfaces that are deflected against each other to neutralize each other's force and produce drag. One of the important issues in control systems is the reduction of disturbing moments. Determining the suitable opening direction with the least drag and disturbing moment and increasing the useful moments is the aim of this research. For this purpose, the measurement of these moments and forces are compared in two states of normal and reverse-opening. The UAV under investigation is a lambda-shaped UAV named Swing. Experiments have been carried out at AOAs of 0 to 12° for three opening angles. The created Mesh is unstructured. In this simulation, the continuity, momentum, and scalar equations have been solved by the Simple C algorithm after discretization with the finite volume method, and the turbulence model (K-ω-SST) has also been used. In this research, the opposite opening direction of the Crow Flap, unlike the usual opening direction mentioned in some articles, had a better result, so that at high AOAs, this opening direction has between 5 and 32% less drag and it has produced 10.5 to 35% more Yawing moment along with reducing disturbing moments.

Improving the aerodynamic performance of vehicles due to the impact on fuel consumption, stability and controllability of vehicles has always been on the attention of engineers. In this study, in order to obtain a brief view of the effectiveness of methods to improve the aerodynamic performance of vehicles, a review of research conducted to reduce aerodynamic forces using the passive flow control method, which can be effective in consideration, implementation and selection of the proper method. The results show the high importance of car body design in reducing drag and lift such that implementing the channel and curvature on the sides of the car to transfer air flow from high pressure areas in front of the body to low pressure areas behind the body has the highest value of reduction in drag force. Also, using a spoiler at the end of the body to delay separation and to direct airflow upwards reduces the lifting force. The effect of these methods on reducing aerodynamic forces is more than other mechanisms, but the exact extent of the effectiveness of each method depends on the type of vehicle and the way of its implementation on the body.

The aerodynamic coefficients of any flying object can be estimated with high accuracy, by aero-ballistic tests, monitored in aerodynamic laboratories. For test-running management, it is necessary to determine the number and type of estimated variables and the station placement of each test. For this purpose, the sensitivity of variables under measurement, in relation to the associated aerodynamic coefficients must be calculated and surveyed. As the trajectory path is a nonlinear equation with six degrees of freedom, in this article we estimate the aerodynamic coefficients and sensitivity of each output to the changes of aerodynamic coefficients using the least square method and fisher data matrix. In other word, if the test data such as the speed and pitch angle are to be measured in an aero-ballistic test, the results of this research can specify their accuracy and sensitivity to each aerodynamic coefficient and the relevant coefficient errors.

The flow separation at the rear of a vehicle generates more pressure drag. A vortex generator can cause delay in developing of separation by chang-ing the distribution of momentum in boundary layer. The comparison be-tween the results of with and without vortex generator reveals the effects of vortex generator on drag reduction considerably. In this study, an effi-cient vortex generator is designed for the Peugeot 405 sedan. The numeri-cal simulations are performed using ANSYS FLUENT and also the model and mesh are generated by ICEM.