Separating and reattaching flows are important in a large number of engineering configurations. The flow through a sudden expansion (backward-facing step) represents a conceptually simple case of this class of flows and hence has been the subject of numerous studies. The present study focuses on the effect of the expansion ratio (defined as the ratio of downstream channel height to upstream channel height) on the unsteady flow features in the reattachment region and further downstream. It is known that this flow demonstrates two different instabilities; the Kelvin-Helmholtz shear layer instability, which scales with the shear layer thickness, and the instability associated with the separation bubble, which scales with the step height and has similarities to K´arman vortex shedding behind a cylinder.In addition to these, there is also a possibility of the presence of the ‘preferred’ mode of the jet issuing from the inlet channel of the sudden expansion, especially at high expansion ratios, where the flow resembles a wall jet. The aim of this study is to investigate experimentally the changes in the instability of the separation bubble, as the expansion ratio is changed, and its possible interactions with the other instabilities in the flow.One might expect some changes in the flow with expansion ratio, as at low expansion ratios, the configuration represents a simple backward-facing step geometry, while at high expansion ratios, the geometry approaches that of a wall jet. A variable expansion ratio backward-facing step facility has been developed in an open circuit wind tunnel.This facility permits continuous variation of the expansion ratio from 1 to around 6. Attention is focused on the turbulent regime of the flow, where the flow structure has been found in previous studies to be relatively insensitive to the Reynolds number. The inlet conditions have been kept constant with a thin turbulent boundary layer at the step, the boundary layer thickness at separation being approximately 14 % of the inlet channel height. The Reynolds number based on the inlet channel height, H, is kept constant at Re=48,000 and the expansion ratio is varied by changing the channel height downstream of the step. Detailed hot wire measurements have been made to characterize the spatial variation of the dominant frequencies in the flow at different expansion ratios. The expansion ratio has been varied from a low value of 1.14 to a high value of 3.25, and detailed measurements are obtained for five expansion ratios of 1.14, 1.3, 1.5, 2.0 and 3.0. Further, to elucidate the dominant vortical structures in the flow, Particle Image Velocimetry measurements have been undertaken simultaneously with hot wire measurements for the case of expansion ratio 1.5, which have permitted the conditional averaging of vorticity fields.These investigations have brought forth some interesting features of the flow over a backward-facing step. Results for the time-mean properties of the flow indicate that the shear layer separating from the step deviates from a free mixing layer behaviour away from the step, possibly due to its interaction with the wall and the recirculation region underneath it. At any given streamwise location, the shear layer momentum thickness, θ, is seen to increase with the expansion ratio. Further, upto reattachment, the momentum thickness of the shear layer is seen to scale with the step height, h, independent of its initial thickness at separation, θo, as long as the boundary layer at separation is sufficiently thin as compared to the step height. Investigations for the unsteady flow features show that the frequency of the dominant peak in the velocity spectrum, supposed to represent the passage frequency (Strouhal number, S, based on the step height, h, and the inlet velocity, U) of the vortical structures, varies in the cross stream (y) direction, in addition to its expected variation in the streamwise (x) direction. The variation of the Strouhal number in the cross stream direction is seen to scale with the local momentum thickness of the shear layer, except for locations very close to the step. To characterize the development of the dominant frequency in the streamwise direction, the maximum value of the Strouhal number at a streamwise location is taken to be the representative value for that streamwise location. The Strouhal number is seen to decrease in the streamwise direction, from a very high value near the step, to a value of approximately 0.08 in the reattachment region, and remains constant further downstream. This value, supposed to represent the large scale structures shed from the reattachment region, is seen to remain very close to 0.08 for all Expansion ratios investigated. Conditional averaging of the vorticity fields in the reattachment region is done for an expansion ratio of 1.5, to get a detailed picture of the unsteady flow field. The hot wire signal at the outer edge of the shear layer in the reattachment region, which represents the non-dimensional structure passage frequency of S=0.08, is used as the conditioning signal. Results seem to indicate that the recirculation region, or the ‘bubble’ divides into two cells, and sheds the downstream cell quasi-periodically. The passage of these structures through the reattachment region seems to be concomitant With a local vertical motion of the shear layer. Further, the streamwise development of the local Strouhal number, Sθ, based on the local momentum thickness of the shear layer, and the local free stream velocity, Umax, indicates a possibility of a coupling between the shear layer and the structures shed from the reattachment region.

An increase in environmental awareness and energy concerns had recently prompted efforts to make pavement construction cheaper and more environmentally friendly. Warm mix asphalt (WMA) is an asphalt mixture production technology that promises to reduce production costs and greenhouse gas emissions. Foamed asphalt binder is increasingly being used to produce WMA. This dissertation addresses several issues related to the use of foamed asphalt binder for WMA applications. The first objective of the research presented in this dissertation is to develop a method and metrics to precisely quantify the characteristics of asphalt binder foams. Laboratory measurements were obtained using the newly developed method to evaluate the extent and stability of foams produced using different asphalt binders at different water contents and laboratory foaming devices. Results demonstrate that the method developed is promising in terms of its ability to provide a detailed history of the behavior of foamed asphalt binder as the foam collapses. In addition, results indicate that the method is sensitive to distinguish between foaming characteristics of different asphalt binders as well as different water contents and foaming devices. The second objective of this study was to relate intrinsic properties of the asphalt binder to its foaming characteristics. A physical model was developed for expansion of asphalt binder foam based on foam physics and fluid mechanics of micro-droplets. The model relates foamant water and asphalt binder mixing efficiency with the surface tension of the asphalt binder. The model can be used to predict which binder can be effectively foamed and used, and whether any chemical modification to the binder is necessary to achieve the same. Results indicate that only a small percentage of water is effective in foaming the asphalt binder. The last objective of this research was to evaluate the influence of foaming on asphalt binder residues and mixture workability and coatability. The influence of foaming process on the rheological properties of asphalt binder residue was investigated. In addition, the significance of foamed asphalt binder characteristics on mixture workability and coatability was evaluated. Results from this last part of the study can be used to optimize binder foaming such that the resulting mixture is coated and compacted without compromising performance. / text

An experimental study was designed to investigate the effect of different parameters on the development and structure of turbulent 3D offset jets. The present investigation considered the effects of offset height ratio, expansion ratio, surface roughness and rib placement on the flow dynamics of a turbulent 3D offset jet. The velocity measurements were performed using an acoustic Doppler velocimetry (ADV) and particle image velocimetry (PIV). Measurements were conducted within the symmetry and lateral planes. For the PIV technique, the measurements in the symmetry and lateral planes were conducted over a streamwise range of 0 ≤ x/bo ≤ 80 and 12 ≤ x/bo ≤ 60, respectively (where bo is the nozzle height). Likewise, velocity measurements using the ADV technique were conducted over a range of 4 ≤ x/bo ≤ 45 in both the symmetry and lateral planes. The velocity measurements were analyzed using both one-point and multi-point statistics. The one-point statistics included profiles of the mean velocities, Reynolds stresses and some of the budget terms in the turbulent kinetic energy transport equation. The quadrant analysis technique was used to investigate the dominant events that contribute towards the Reynolds shear stress. The two-point correlation analysis was used to investigate how the turbulence quantities are correlated. Information obtained from the two-point correlation analysis was also used to investigate the inclination of vortical structures within the inner and outer shear layers of the 3D offset jet. The direction of the positive mean shear gradient played an active role in the inclination of these vortical structures within the inner and outer shear layers. The reattachment process resulted in the breakdown of these structures within the developing region. Similarly, various length scales were estimated from these structures. The proper orthogonal decomposition was used to examine the distribution of the turbulent kinetic energy within the offset jet flow. Also, the dynamic role of the large scale structures towards the turbulent intensities, turbulent kinetic energy and Reynolds shear stress was investigated. / October 2016

The thesis is focused on the proposal of production of a stamped part of the uni-axial rod located in the axle of the truck. The uni-axial rod is made of materiál S420MC with thicknes of 4 mm and the planned series production is 84 000 pieces per year for 7 years. The most difficult point for production is a collar, which create support of the bushing. It is not posibble to produce a required height with conventional one-stage process, which was experimentally verified. In the programm PAM-STAMP there was designed multiple-stage process of the production with the use of numerical simulation. The progressive die was designed for this process of the production. Maximal load of a forming press is 5 057 kN. Production will be located on the forming press Kaiser 8000-50-F5-RKM by ANDRITZ Metals. Maximum force of the forming press is 8 000 kN.