Drag measurements for excrescence arrays of square section mounted on a smooth wall and subjected to two adverse pressure gradients in equilibrium are obtained. Differences in drag which arise when the excrescences are uniformly distributed and when tending to isolation are shown. Flow visualization photographs using the surface oil flow technique are presented to illustrate different flow patterns around arrays of varying spacing. A prediction model for the drag of excrescence arrays based on the results obtained was devised. Its range of application could be extended to excrescences of varying shape providing they are sufficiently small to be immersed in the logarithmic part of the boundary layer. Drag results are determined by both a momentum defect and a pressure distribution technique. These results are compared and the difference between them is partially attributed to the change in surface friction between the excrescences and partially to some lack of two-dimensionality in the test procedure. Corrections for the latter effect are made to the data obtained.

No description available.

Includes bibliographical references. / This thesis deals with a system that reduces the oncoming boundary layer displacement thickness in a wind tunnel. The device is then used to examine the effect that this boundary layer has on the aerodynamic drag of a standard truck, which is classified as a bluff body with a high ground clearance and the same truck fitted with skirts all round, which is then classified as a bluff body with a low ground clearance. To gain insight into this field of industrial aerodynamics, an extensive literature survey was done in which all the relevant SAE papers onwards from the late sixties were studied and summarised in the first section of this report. The second section deals with a system that can limit the boundary layer displacement thickness in the test section of the 3/4 open jet wind tunnel. Through investigations and an extensive literature research a suction device was designed and built. This boundary layer removal system was then tested to ensure that the main flow indicators are not influenced by the suction and thus lie within internationally accepted limits. Included in this section are a description of the truck model and the other instruments or devices used to complete the testing. The third section deals with the aerodynamic drag experienced by the bluff body with a high ground clearance. Included in the third section is an investigation that deals with the aerodynamic drag of the same truck model, when skirting has been added which considerably lowers the ground clearance. The results obtained from the above investigations indicate that the drag of the Ground Simulation model without skirts is increased by about 3.8% with the removal of the boundary layer and up to 10% for the model with the skirts. It is thus shown that the farther the object protrudes into the boundary layer, the larger the increase in drag will be once this boundary layer has been removed. These figures were obtained from testing the model at 22.2m/s free stream velocity and a 6mm wheel-ground clearance, with the wheels rotating.

The accuracy of existing methods for estimating the drag based on experimental flow field measurements were assessed for two-dimensional bodies. The effects of control volume boundary placement and inherent simplifying assumptions were also investigated. Wind tunnel experiments were performed on a circular cylinder operating at a Reynolds number of 8,000 and 20,000, and on a NACA 0018 airfoil operating at a chord Reynolds number of 100,000 for three angles of attack (α), specifically, 5◦, 10◦, and 15◦. The circular cylinder experiments fall within the the shear layer transition flow regime. Airfoil investigations span both types of flow development common to low Reynolds number airfoil operation. For α = 5◦ and 10◦, a separation bubble forms on the upper surface of the airfoil, while, for α = 15◦, the flow separates without reattaching, resulting in a stalled airfoil. Wake velocity and pressure measurements were performed at several downstream locations to investigate the impact of control volume boundary placement. Wake profiles were measured between 3 and 40 diameters downstream from the circular cylinder axis and between 1 and 4.5 chord lengths from the trailing edge of the airfoil. In addition to wake profiles, the outer flow velocity variation was quantified to investigate the appropriate location to measure freestream flow characteristics in a test section with streamwise-varying outer flow conditions. The results show that drag estimates are strongly dependent on the streamwise position of the measured wake profile for all methods investigated. Drag estimates improved, and streamwise variation decreased, with increasing streamwise position of the flow measurements. For the pressure based method examined, wake measurements should be taken at least 10 times the projected model height downstream of the model. In the case of the circular cylinder, this is equivalent to 10 diameters and, for the airfoil investigated, it is approximately 1 chord length from the trailing edge. For the methods relying on velocity measurements, acceptable estimates of drag were possible when based on measurements taken at least 30 projected heights downstream, i.e., 30 diameters for the circular cylinder and 3 chord lengths for the airfoil model investigated. The findings highlight the importance of providing a detailed description of the methodology and experimental implementation for drag estimates based on flow field measurements. Finally the study offers guidelines for implementing momentum integral based drag calculations in future investigations.

This thesis deals with road loads, coastdown tests and evaluation of measured data. Thesis consists of two main parts: theoretical and computational. The first part describes road loads with focus on aerodynamic drag and lift force. In the second part, a software tool for processing the measurement per ISO 10521-1 is designed and lift force measured with running resistance method is calculated.

The master's thesis deals with the aerodynamic interaction od two vehicles, modelling in CFD software, how the vehicle behaves in leeward.

The master's thesis deals with the aerodynamic interaction od two vehicles, modelling in CFD software, how the vehicle behaves in leeward.

This thesis deals with the effect of the aerodynamic forces on a vehicle. It contains the description of the test run of the vehicle, the proposal on how to process the measurements, the processing of the measurements themselves, and the final assessment of the results as to their accuracy and the possibility of repeating the experiment. Furthermore, this thesis contains the comparison of the effect of the individual aerodynamic features on the race car.

Dois dos principais objetivos no estudo da aerodinâmica de veículos comerciais são a redução no consumo de combustível e o aumento na eficiência da refrigeração do motor. Esses objetivos podem ser alcançados através do desenvolvimento de dispositivos que modifiquem o escoamento do ar ao redor do veículo e também através da alteração da forma das superfícies externas. A inclinação das superfícies da parte traseira de um ônibus, por exemplo, tem grande influência sobre a esteira turbulenta que se forma atrás do veículo. O uso de ferramentas computacionais permite uma redução de custo e maior flexibilidade na análise aerodinâmica de autoveículos. Ainda é preciso, no entanto, que o resultado dessas ferramentas computacionais seja verificado com o maior número possível de casos para que se possa escolher e ajustar o modelo matemático de forma adequada. O objetivo do presente trabalho é a verificação dos resultados computacionais e experimentais no desenvolvimento de metodologias que visem à redução no consumo de combustível e aumento na eficiência da refrigeração do motor. Foram comparados resultados experimentais e computacionais do escoamento sobre um modelo de um ônibus comercial em escala 1:17,5. Para a realização do experimento foi utilizado um túnel de vento de seção aberta, onde foram analisadas as distribuições de pressão nas superfícies da carroceria e o arrasto aerodinâmico. Para o teste computacional, foi utilizado um software de dinâmica dos fluidos computacional em que as equações de Navier-Stokes com média de Reynolds são resolvidas pelo método dos volumes finitos usando um modelo de turbulência RNG 'capa' - 'épsilon' / Two main objectives in the study of commercial vehicle aerodynamics are the reduction in fuel consumption and the improvement in engine refrigeration efficiency. These objectives can be achieved through development of devices which vary the flow characteristics around the vehicle and also through modification of the shape of external surfaces. The slope of rear surfaces, for instance, has large influence over the wake turbulence which forms behind the vehicle. The use of computational tools yields cost reduction and greater flexibility in automotive aerodynamic analysis. There is still a need, however, for verification of results, generated by these computational tools, with the largest possible number of test cases so that the mathematical model is adequately chosen and adjusted. The objective of the present work is the verification of experimental and computational results in the development of methodologies aiming at reduction of fuel consumption and improvement in engine refrigeration efficiency. Experimental and computational aerodynamic results were compared for a commercial bus model with a 1:17.5 scale. The experiments were conducted in an open section wind tunnel where pressure distribution and aerodynamic drag were analyzed. The numerical analysis was conducted using computational fluid dynamics software which solves the Reynolds Averaged Navier-Stokes equations using the finite volume method with a RNG 'capa' - 'épsilon' turbulence model

Dois dos principais objetivos no estudo da aerodinâmica de veículos comerciais são a redução no consumo de combustível e o aumento na eficiência da refrigeração do motor. Esses objetivos podem ser alcançados através do desenvolvimento de dispositivos que modifiquem o escoamento do ar ao redor do veículo e também através da alteração da forma das superfícies externas. A inclinação das superfícies da parte traseira de um ônibus, por exemplo, tem grande influência sobre a esteira turbulenta que se forma atrás do veículo. O uso de ferramentas computacionais permite uma redução de custo e maior flexibilidade na análise aerodinâmica de autoveículos. Ainda é preciso, no entanto, que o resultado dessas ferramentas computacionais seja verificado com o maior número possível de casos para que se possa escolher e ajustar o modelo matemático de forma adequada. O objetivo do presente trabalho é a verificação dos resultados computacionais e experimentais no desenvolvimento de metodologias que visem à redução no consumo de combustível e aumento na eficiência da refrigeração do motor. Foram comparados resultados experimentais e computacionais do escoamento sobre um modelo de um ônibus comercial em escala 1:17,5. Para a realização do experimento foi utilizado um túnel de vento de seção aberta, onde foram analisadas as distribuições de pressão nas superfícies da carroceria e o arrasto aerodinâmico. Para o teste computacional, foi utilizado um software de dinâmica dos fluidos computacional em que as equações de Navier-Stokes com média de Reynolds são resolvidas pelo método dos volumes finitos usando um modelo de turbulência RNG 'capa' - 'épsilon' / Two main objectives in the study of commercial vehicle aerodynamics are the reduction in fuel consumption and the improvement in engine refrigeration efficiency. These objectives can be achieved through development of devices which vary the flow characteristics around the vehicle and also through modification of the shape of external surfaces. The slope of rear surfaces, for instance, has large influence over the wake turbulence which forms behind the vehicle. The use of computational tools yields cost reduction and greater flexibility in automotive aerodynamic analysis. There is still a need, however, for verification of results, generated by these computational tools, with the largest possible number of test cases so that the mathematical model is adequately chosen and adjusted. The objective of the present work is the verification of experimental and computational results in the development of methodologies aiming at reduction of fuel consumption and improvement in engine refrigeration efficiency. Experimental and computational aerodynamic results were compared for a commercial bus model with a 1:17.5 scale. The experiments were conducted in an open section wind tunnel where pressure distribution and aerodynamic drag were analyzed. The numerical analysis was conducted using computational fluid dynamics software which solves the Reynolds Averaged Navier-Stokes equations using the finite volume method with a RNG 'capa' - 'épsilon' turbulence model