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Abstract This study investigates the yaw angle effect on the aerodynamic performance of a hatchback model fitted with a roof spoiler. Although the aerodynamic performance of road vehicles is highly dependent on its yaw angle, it has rarely been considered in studies pertaining to roof spoiler applications. Two common types of spoilers are studied, namely, strip and wing types. The hatchback model is based on the Ahmed body at 35 ° slant angle. The yaw angle affects the aerodynamic performance of the hatchback model negatively regardless of the presence of a spoiler. However, the impact is more pronounced with the absence of a spoiler, particularly at higher yaw angles. Most importantly, the use of a spoiler prevents the bi-stability behaviour of flow which occurred in the model without the spoiler. Furthermore, the strip spoiler reduces both the drag and lift coefficients (C d and C l), whereas the wing type results in a greater reduction in C l while penalising C d. The results of the surface pressures indicate that the changes in the flow around the rear slanted body are the main factors affecting the aerodynamic performance of the hatchback model using the spoiler. Highlights • The non-symmetric bi-stable flow are detected for the Ahmed body at critical yaw angle. • Use of spoilers prevented bi-stable flow. • Strip spoiler reduced both the drag and lift coefficients. • Rear wing produced greater reduction in lift coefficient while penalising drag coefficient. [ABSTRACT FROM AUTHOR]

A consistent mesh refinement study, relating to the prediction of aerodynamic forces about an experimentally validated reference train geometry, is presented in this paper. The flow about a high-speed train has a multi-scale character which poses challenges for the design of computationally effective meshes. The purpose of this study is to assist in the development of guidelines for effective drag prediction of high-speed trains using numerical simulation. These guidelines should assist CFD practitioners by identifying the regions of the mesh that are critical for the correct estimation of drag as well as providing information on appropriate mesh characteristics, such as volume and surface element length scales. Numerical assessments are validated against an experimental drag measurement program and the extent to which RANS is sufficiently predictive for industrial design is discussed. The results obtained in the work suggest that the mesh about the train nose is essential for the proper assessment of the aerodynamic drag acting on the vehicle. [ABSTRACT FROM AUTHOR]

The effects of deflectors on the aerodynamic drag and near wake of an Ahmed model with a 25° slant angle were experimentally investigated. Experiments were conducted in a closed circuit low speed wind tunnel at a Reynolds number of 8.7×10 5 , based on the free stream oncoming velocity ( U ∞ ) and model length ( l ). The deflectors were placed at the side edges and leading edge of the slant. The height or width of the deflectors was 1%, 2% and 3% of l . Pressure distribution on the rear slanted surface and the vertical base was measured using pressure scanners. The flow velocities and static pressure were measured by Cobra probe at 0.5 l and l downstream in the near wake. Oil film flow visualization technique was deployed to capture the flow structure on the slant. In the absence of control, shear layer separation from the side edges and leading edge of the slant results in remarkable local low pressure regions on the slant, which contribute significantly to the aerodynamic drag. There is a D-shape separation bubble on the slant and the near wake is dominated by one pair of counter rotating trailing vortices. When the height of the deflector placed at the side edges of the slant is 1% of l , its effects on the near wake are negligibly small and the corresponding drag is increased slightly, compared to the uncontrolled case. With the deflector height increased to 2% and 3% of l , the D-shape separation bubble and the trailing vortices were noticeably suppressed, with the drag reduction reaching 3.5% and 7.2%, respectively. The deflector at the leading edge of slant changes the near wake of the model similar to that behind an Ahmed model of larger slant angle (e.g. 30° or 35°), eliminating the D-shape separation bubble on the slant. The corresponding drag reduction reaches 9.3%, 10.7% and 10.9% for the deflector width of 1%, 2% and 3% of l , respectively. For the 25° slant Ahmed model, the deflector placed at the leading edge of the slant is more efficient in reducing drag and suppressing the trailing vortices than those at the side edges of slant. [ABSTRACT FROM AUTHOR]

The aerodynamic loadings of a 5:1 rectangular cylinder in one-dimensional sinusoidal flows are experimentally tested in a multiple-fan active control wind tunnel. A series of single-frequency streamwise sinusoidal flows, which are fully coherent in the spanwise direction, are generated by changing the frequency and amplitude. Spectral analysis indicates that the total drag, lift forces, and pitching moment contain the inflow-induced components as well as those induced by vortex shedding. To identify the two-dimensional aerodynamic admittances (2D AAF), the vortex-induced components are separated from the inflow-induced components by using the POD method. Subsequently, the 2D AAFs of the drag, lift forces and pitching moment are identified and compared with the empirical or theoretical models. Results show that the inflow amplitude has a limited influence on the 2D AAFs, while the angle of attack (AoA) can cause significant changes in them. At a zero AoA, the 2D drag AAF is in alignment with the Davenport function and the 2D lift AAF is close to Horlock's AAF at low frequencies. Meanwhile, the 2D drag AAF is less influenced by the AoA than the lift and moment AAFs. The relationships between the inflow-induced and vortex shedding-induced components of the total forces are also discussed. The two-dimensional drag, lift, and moment aerodynamic admittances of a 5:1 rectangular cylinder are experimentally identified in one-dimensional streamwise sinusoidal flows. The vortex-induced components of total forces are separated from the inflow-induced ones and the latter is utilized to identify the two-dimensional aerodynamic admittances. Results show that the inflow amplitude has limited influences on the 2D AAF, while the angle of attack (AoA) causes significant changes in them. At zero AoA, the 2D drag AAF is in agreement with Davenport's AAF, and the 2D lift AAF is close to the Horlock's AAF at low frequencies (ω ​≤ ​5). On the other hand, the 2D lift and moment AAF at zero AoA are much higher than those at non-zero AoAs, indicating more unsteady features. The present method can be applied in the buffeting analyses of large-span line-like structures. Image 1 • Aerodynamic forces on a 5:1 rectangular cylinder are measured in sinusoidal flows. • Inflow-induced and vortex-induced components of the total forces are separated. • Two-dimensional drag, lift, and moment aerodynamic admittance (AAF) are identified. • Effects of inflow amplitude and attack angle on the AAFs are analyzed. [ABSTRACT FROM AUTHOR]

Wind tunnel experiments on flow interference of adjacent (spacing ratio P / B ​= ​1.75) twin square cylinders in various attack angles α were conducted at a Reynolds number of 8.0 ​× ​104 considering both horizontal and diagonal arrangements of models. Investigations on the mean and fluctuating aerodynamic force coefficients, mean and fluctuating wind pressure coefficients, spanwise correlations, power spectrum densities (PSD) of lift, and Strouhal numbers of two cylinders, as well as the inter-cylinder correlations between them, are presented. The results show that the aerodynamic characteristics of two diagonal cylinders differ significantly from those of horizontal ones. Compared with the single-cylinder, the pressure distributions on adjacent cylinders are dramatically changed, leading to the negative drag, attractive lift, or repulsive lift on the downstream cylinder. At small α , diagonal cylinders present stronger mean drag and higher fluctuating forces than horizontal cylinders do. Besides, a stronger spanwise correlation is found for the diagonal ones. The vortex shedding pattern can be divided into four stages for the horizontal arrangement and six for the diagonal case. PSD curves and Strouhal numbers are similar between two cylinders for both arrangements, suggesting that the two closely spaced cylinders act like one bluff body in the vortex shedding. • Horizontal and diagonal cylinders have quite different aerodynamic properties. • Two closely spaced square cylinders act like one bluff body in vortex shedding. • Negative drag and attractive lift on the downstream cylinder exist at α ​≤ ​30°. [ABSTRACT FROM AUTHOR]

This study deals with the effects of wind turbulence on the mean aerodynamic drag, lift and moment coefficients of a stationary ice-accreted section model of a bridge cable for different wind angles of attack. The experiments were conducted in the Reynolds number range between 2.5·104 and 1.36·105. While the yawed/inclined cable model was experimentally iced in a climatic wind tunnel, the development of the ice shape was registered using photogrammetry. Later on, the ice-accreted model was reproduced on a smaller scale via three-dimensional printing. For the model in cross-flow, a series of wind tunnel tests were performed in low and moderately turbulent flow conditions with turbulence intensities of 3% and 12%, respectively. The obtained results were compared with those obtained experimentally for a circular smooth cylinder. The principal finding is that the flow turbulence significantly reduces the drag coefficient. • The experimental process was conducted to create an ice accretion on a cable model. • The ice-accreted model was reproduced in smaller scale by 3D printing method. • The aerodynamic coefficients were tested in low and moderately turbulent wind. • The effect of wind turbulence on aerodynamic coefficients was examined. [ABSTRACT FROM AUTHOR]