Experimental Study of the Skin-Friction Topology Around the Ahmed Body in Cross-Wind Conditions

In this study, skin friction around a ½-scale Ahmed body was measured experimentally at a Reynolds number of Re = 2×105. The slant angle of the Ahmed body was 25° and the yaw angles ranged from 0° to 8°. This study focused on the flow structure on the slant surface under different cross-wind conditions. A force balance system was applied to measure the aerodynamic drag of the model. The global skin-friction topology was measured by applying a luminescent oil layer with a sub-grid data processing algorithm. The method used to measure the skin friction was conducted for the first time on the Ahmed body. The results indicated that the technique is highly capable of extracting the skin-friction topology. For a yaw angle below 3°, the flow on the slant surface was not significantly affected by the cross-wind condition and the drag of the model was nearly constant. However, at yaw angles above 3°, the flow on the slant surface was highly affected by the roof longitudinal vortexes on the windward side, leading to a dramatic increase in the drag of the model. High consistency in the drag and skin-friction fields was observed. The detailed skin-friction structure at different yaw angles will be discussed in this study.

The Effect of Single Dielectric Barrier Discharge Actuators in Reducing Drag on an Ahmed Body

The feasibility of a single dielectric barrier discharge (SDBD) actuator in controlling flow over an Ahmed body, representing a simplified car model, has been numerically and experimentally investigated at Reynolds numbers of 7.68×105 and 2.25×105. The Ahmed body had slant angles of 25∘ and 35∘. The results showed that SDBD actuators could significantly enhance the aerodynamic performance of the Ahmed body. Several arrangements of the actuators on the slant surface and the rear face of the model were examined to identify the most effective arrangement for drag reduction. This arrangement resulted in an approximately 6.1% drag reduction. This improvement in aerodynamic performance is attributed to the alteration of three-dimensional wake structures due to the presence of SDBD, which coincides with surface pressure variations on the slant and rear faces of the Ahmed body.

Experimental Study of Flow Control Over a Standard Road Vehicle Using Plasma Actuator

Ahmed Body is a standard and simplified shape of a road vehicle that's rear part has an important role in flow structure and it's drag force. In this paper flow control around the Ahmed body with the rear slant angle of 25° studied by using the plasma actuator system situated in middle of the rear slant surface. Experiments conducted in a wind tunnel in two free stream velocities of U = 10m/s and U = 20m/s using steady and unsteady excitations. Pressure distribution and total drag force were measured and smoke flow visualization carried out in this study. The results showed that at U = 10m/s using plasma actuator suppress the separated flow over the rear slant slightly and be effective on pressure distribution. Also, total drag force reduces in steady and unsteady excitations for 3.65% and 2.44%, respectively. At U = 20m/s, using plasma actuator had no serious effect on the pressure distribution and total drag force.

Experimental Study of Flow Control Over an Ahmed Body Using Plasma Actuator

Ahmed Body is a standard and simplified shape of a road vehicle that's rear part has an important role in flow structure and it's drag force. In this paper flow control around the Ahmed body with the rear slant angle of 25° studied by using the plasma actuator system situated in middle of the rear slant surface. Experiments conducted in a wind tunnel in two free stream velocities of U = 10 m/s and U = 20 m/s using steady and unsteady excitations. Pressure distribution and total drag force was measured and smoke flow visualization carried out in this study. The results showed that at U = 10 m/s using plasma actuator suppress the separated flow over the rear slant slightly and be effective on pressure distribution. Also total drag force reduces in steady and unsteady excitations for 3.65% and 2.44%, respectively. At U = 20 m/s, using plasma actuator had no serious effect on the pressure distribution and total drag force.

Wake Flow Visualization of a Simplified Vehicle Model During Flow State Change

A flow around a three-dimensional bluff body such as an automobile sometimes exhibits a bi-stable state wherein two stable flow states exist for a single condition. Better aerodynamic characteristics can be obtained if we suppress or promote the flow state change between such bi-stable states. Hence, it is necessary to understand the trigger conditions and process of the flow state change. In this study, we investigated the transient aerodynamics of the Ahmed model with the slant angle of 32°, exceeding the critical angle of 30°, known to exhibit bi-stable state under crosswind conditions. Changing the Yaw angle by rotating the model, produced change in the flow state, accompanied by time delay. While continuously measuring fluid force, we performed PIV measurement triggered by a sudden change in fluid dynamic force corresponding to the flow state change. Using these methods, we realized the synchronous measurement of the fluid force and wake flow during the flow state change. At the beginning of the flow state change, flow velocity changed around the trailing edge of the slant surface. Subsequently, the separated flow above the slant surface increased. A gradual decrease of drag coefficient was observed before the flow state change though flow behavior associated with the drag change was not observed in the velocity field of PIV measurement.

A Numerical Study on Vibrations of a Roller Bearing With a Surface Crack in the Races

Vibrations of roller bearings will be affected when a surface crack is caused in the bearing system. Thus, it is very helpful to study relationships between the sizes of the surface crack and vibrations of the bearings for detecting and diagnosing the surface crack in the bearing systems. In this study, a dynamic finite element model for a roller bearing with a vertical or slant surface crack on its outer race is presented using an explicit dynamic finite element software package. All components of the roller bearing are formulated as elastic bodies in the finite element model, which can consider the elastic deformations in the bearing system. Effects of the depth and slope angle of the surface crack on the contact forces between the roller and races of the bearing are studied, as well as the vibrations of the bearing. The simulation results show that the explicit dynamic finite element analysis method can be applied for studying the vibration characteristics produced by a vertical or slant surface crack in roller bearings.

Drag Reduction on the 25-deg Ahmed Model Using Fluidic Oscillators

Transportation of goods and people involves moving objects through air, which leads to a force opposing motion. This drag force can account for more than 60% of power consumed by a ground vehicle, such as a car or truck, at highway speeds. This paper studies drag reduction on the 25-deg Ahmed generic vehicle model with quasi-steady blowing at the roof–slant interface using a spanwise array of fluidic oscillators. A fluidic oscillator is a simple device that converts a steady pressure input into a spatially oscillating jet. Drag reduction near 7% was attributed to separation control on the rear slant surface. Particle image velocimetry (PIV) and pressure taps were used to characterize the flow structure changes behind the model. Oil flow visualization was used to understand the mechanism behind oscillator effectiveness. An energy analysis suggests that this method may be viable from a flow energy perspective.

“8 Plate”: An Alternative Device to Fix Highly Recurrent Traumatic Anterior Gleno-Humeral Instability in Patients with Severe Impairment of the Anterior Capsule

Background: There is still debate about the best treatment option for highly recurrent anterior shoulder dislocation in patients with severe impairment of the anterior capsule and/or recurrence after either arthroscopic or open capsulorrhaphy. Materials and Methods: The clinical and radiological findings of 7 patients treated with an open capsulorrhaphy stabilized with an “8 plate” for a highly recurrent traumatic anterior shoulder dislocation with severe impairment of the anterior capsule and a large Bankart lesion were retrospectively reviewed. Follow-up evaluation included VAS for pain, Constant-Murley, Simple Shoulder Test, ASES, UCLA, Quick DASH, Rowe, Walsch-Duplay scores, as well as X-rays of the operated shoulder. Results: At follow-up none of the patients reported subsequent dislocations. Range of motion of the shoulder was complete in all cases, but one. Results of the functional scoring systems were satisfactory. X-rays showed no osteolysis and good position of the plate. Conclusion: To our knowledge, this is the first report in the literature about an open capsular tensioning and Bankart lesion repair performed with an “8 plate”. We believe that this is a reliable and effective procedure to address traumatic anterior re-dislocation of the gleno-humeral joint when the capsule is extensively torn and frayed or in revision cases. Moreover the “8 plate” is ideal to be applied in such a narrow space on the slant surface of the scapular neck close to the glenoid rim.

Effect of KIII on Fatigue Crack Growth Behavior

In this study, mixed-mode fatigue tests are conducted using surface-cracked specimens. Slant surface-cracked specimens are prepared with crack angles of 15 deg, 30 deg, 45 deg, and 60 deg. It is shown that a “factory roof” fracture is formed at the deepest point of the surface crack due to ΔKIII and causes the crack growth rate to decrease. Additionally, fatigue crack growth is simulated using the superposition finite element method (FEM) with crack growth criteria. It is shown that conventional crack growth criteria are not applicable to factory roof fractures. Finally, a modified criterion for the prediction of crack growth rate is proposed, fatigue crack growth simulation is conducted using this criterion, and the results are compared with experimental results.

Numerical Simulation of Solid-Liquid Multiphase Flow in Horizontal Flexural Pipes

We need to hold flow characteristic for water- and/or oil-sediments, with low-middle volume fraction of the particles in horizontal flexural pipes, in order to design logging tool and build interpretation methods for the producing profile. To achieve this, we built governing equations and boundary conditions for the water- and/or oil-sediments based on the mixture algebraic slip model (MASM), and gained numerical solution by the finite difference method and the successive over relaxation. 3-D simulation results in flexural horizontal pipes indicated that volume of oil is obviously greater than that of water in the downhill but opposite in upgrade. When the velocity in the entrance is small enough, “die oil” perhaps presents at top of the borehole in downhill. Moreover, this entrance velocity arisen “die oil” is increasing with height of interface. The volume of deposited particle in lowest location is reducing with increasing the entrance velocity when the entrance velocity is small and increasing with the entrance velocity when the entrance velocity is large, and slant surface of deposited particle volume is gradually emerged. This is due that deposited particles are hiked once again and carried forward when the flow velocity is greater than incipient velocity for a particle size.