Investigation of aerodynamic drag reduction devices in automotive engineering

Ovaj diplomski rad je dio razvojnog procesa u području aerodinamike u projektu CULT. Glavni zadatak diplomskoga rada su uređaji za smanjenje aerodinamičkog otpora zraka za vozila koja pripadaju A-segmentu. Ti uređaji služe kako bi utjecali na strujanje zraka oko vozila s ciljem smanjenja aerodinamičkog otpora. Na vozilu CULT nalazi se nekoliko takvih uređaja, koje je potrebno optimirati. Jedan primjer su bočna osvrtna zrcala – retrovizori, koji su oblikovani na način da utječu na strujanje zraka iza automobila smanjujući aerodinamičke gubitke u vrtložnom tragu. Konstrukcija retrovizora opisana je u poglavlju 3., a njihova optimizacija u poglavlju 7. Istraživanje u ovome radu je napravljeno pomoću CFD-a (eng. Computational Fluid Dynamics – Računalna dinamika fluida), te su numerički rezultati su uspoređeni i potvrđeni s mjerenjima u zračnom tunelu. Drugi zadatak rada je prikazati cjelokupni proces aerodinamičke optimizacije pomoću CFD-a u automobilskoj industriji – od CAD površina do analize CFD rezultata. Analiza numeričkih i eksperimentalnih rezultata u ovom istraživanju je pokazala da se značajno smanjenje aerodinamičkog otpora može postići sa samo malim izmjenama na geometriji automobila. Pozivajući se na primjer iznad, dokazano je da retrovizori mogu služiti kao uređaji za smanjenje aerodinamičkog otpora zraka.This thesis is a part of the project CULT (Cars’ Ultra Light Technologies), carried out by the company Magna Steyr, Graz, Austria. The CULT vehicle is a small city car, belonging to the A-segment vehicles with 4 seats. The main idea of the project is to develop a realistic, production-ready vehicle with CO2 emissions of only 49g/km. In order to achieve this goal, large efforts in aerodynamics development are inevitable, especially the aerodynamic drag should be as low as possible. Main objective in this thesis is to investigate various drag reduction devices for A-segment vehicles. One example are side mirrors (rear-view mirrors), which are designed with the idea influencing the flow at the back of the car and reducing aerodynamic losses in the wake behind the car. Investigation work in this thesis is carried out with the help of Computational Fluid Dynamics (CFD) and numerical results are validated against the results from the wind-tunnel measurements. In the last decades CFD has become very popular engineering tool in automotive industry. In early stages of vehicle development CFD offers clear advantages compared to the classic wind tunnel testing. Smart and parallel usage of these two methods represents a successful formula for good aerodynamic optimization, not only in automotive industry but also in other branches of modern engineering. Another objective of this thesis is to show the complete CFD process in automotive aerodynamics – from design of CAD surfaces to the analysis of CFD results. Understanding of this process is very important for the correct application of CFD in design and development of new cars, especially for a young engineer starting his/her professional career in automotive industry. Analysis of numerical and experimental results in this investigation showed that considerable drag reduction can be achieved with only small changes of vehicle geometry. Referring to the example above, it was proved that side mirrors can serve as drag reduction devices