Improving Aerodynamic Performance of a Truck: a Numerical Based Analysis

With a change in EU-legislation regarding the dimensions of heavy trucks [1] coming up, specifically allowing aerodynamic devices fitted to the back of trailers, the transportation industry is set to largely decrease its environmental impact in the near future. These aerodynamic devices have been researched for quite some time [2] but have not yet gained widespread market acceptance, partly because of the transportation industry’s complex owner structures and partly because of size regulations of the past. Though with this new legislation and other expected new EU-legislation on CO2 emissions, development of these aerodynamic devices looks set to become a field of intense study. The study explores different options regarding the influence of changing the rear shape of a generalized ground transportation system (GTS), a simplified model of a truck geometry. By changing the rear shape the drag force induced by the oncoming air flow was reduced, and the overall coefficient of drag (CD) value lowered. There is also an investigation as to how an added suction slot, and that slots location, affects the CD. Computational Fluid Dynamics (CFD) in the form of the commercial computer software STAR-CCM+ was used to simulate the flow around the GTS, and the results were verified with similar studies and experiments [3] on the same geometry. RANS equations and Menter k-! SST turbulence model was used for all simulations. The results show that CD can be lowered by 21% compared to a baseline case. Further on the added suction slots can reduce drag, but depending on slot location also can add to the drag force experienced by the GTS

Scanning tunneling microscope study of the morphology of chemical vapor deposited copper films and its correlation with resistivity

In this article we report the results of the scanning tunneling microscope study of the surface morphology of copper films grown by metalorganic chemical vapor deposition from the precursor $Cu(tbaoac)_2$. Films$\infty$100 nm in thickness were grown by varying the reactor pressure. The images reveal the crucial role of the reactor pressure and growth rate on the morphology and grain growth of the films. Films grown at a low growth rate have a smooth surface with small well connected grains of $\infty$10–40 nm diameter with relatively lower resistivity, while films grown at higher growth rates have rougher surfaces and larger grain sizes of $\infty$10–100 nm diameter with poor connectivity that leads to higher resistivity. The correlation of the morphology with resistivity ($\rho$) and the temperature dependence of $\rho$ in the range 300–4.2 K was investigated. Comparison with the $\rho$ of pure bulk copper shows that these films have much higher resistivities. A large part of the high resistivity at room temperature arises from an enhanced temperature dependent part of $\rho$ and is not due to an enhancement of the residual resistivity alone. The films exhibit deviations from Matthiessen’s rule. From a semi-quantitative analysis of the data using existing theories we could assign the large $\rho$ as well as the temperature dependence of $\rho$ to grain boundary scattering and surface scattering. However, for T>50 K we find that an extra temperature dependent $\rho$ term which may be related to enhancement of electron-phonon interactions by the rough film surface is required

Scanning tunneling microscope study of the morphology of chemical vapor deposited copper films and its correlation with resistivity

In this article we report the results of the scanning tunneling microscope study of the surface morphology of copper films grown by metalorganic chemical vapor deposition from the precursor Cu(tbaoac). Films ≈100 nm in thickness were grown by varying the reactor pressure. The images reveal the crucial role of the reactor pressure and growth rate on the morphology and grain growth of the films. Films grown at a low growth rate have a smooth surface with small well connected grains of ≈10-40 nm diameter with relatively lower resistivity, while films grown at higher growth rates have rougher surfaces and larger grain sizes of ≈10-100 nm diameter with poor connectivity that leads to higher resistivity. The correlation of the morphology with resistivity (ρ) and the temperature dependence of ρ in the range 300-4.2 K was investigated. Comparison with the ρ of pure bulk copper shows that these films have much higher resistivities. A large part of the high resistivity at room temperature arises from an enhanced temperature dependent part of ρ and is not due to an enhancement of the residual resistivity alone. The films exhibit deviations from Matthiessen's rule. From a semi-quantitative analysis of the data using existing theories we could assign the large ρ as well as the temperature dependence of ρ to grain boundary scattering and surface scattering. However, for T>50 K we find that an extra temperature dependent ρ term which may be related to enhancement of electron-phonon interactions by the rough film surface is required