Validated CFD simulations of vortex formation in jet engine test cells

Vortices can be produced and ingested in to the intake of a jet engine during its operation. This can occur when the plane is on the runway during take-off, or during engine tests in a test cell. The vortex can throw debris into the intake or stall the compressor, causing severe damage to the engine. The runway problem is solved by keeping the runway clear of debris and scheduling the throttle appropriately. However vortices can still occur in test cells. To eliminate vortices at the design stage it is necessary to be able to predict the onset of the vortex. This paper seeks to use the commercial CFD code Fluent to investigate both the runway and test cell problem. The runway problem has been investigated in previous wind tunnel studies by other authors. These studies were recreated in a CFD simulation reported in detail elsewhere. The threshold conditions for vortex formation were located and the effects of suction tube diameter, shear in the test cell inlet, ground boundary layer thickness and suction inlet Reynolds number were investigated. With the computational techniques thus validated, the study is extended to enclosed test cell geometries. The simulations show three stages of flow regime namely regular vortex, deformed vortex and no vortex. Vortices are not formed at cell bypass ratios greater than 50-70% and stable vortices are formed at cell bypass ratios less than 20-30%. The vortex threshold is found to be lower than the threshold for suction over ground plane simulations on the Vi/Vo against H/Di graph, i.e. vortex formation occurs over a wider range of conditions when the flow is enclosed

THE CHARACTERISTICS OF DOUBLE KICK IN THE AIR DURING ACTIVE AND PASSIVE ATTACK FOR ELITE TAE-KWON-DO ATHLETES

The purpose of this study is to discuss the reaction time and movement time of the double kick in the air (DKA) of the active and passive attacks for elite tea-kwon-do athletes. The experiment takes six male tae-kwon-do athletes (average age: 20.5 yearold; average height: 174.8cm; average weight: 63kg) who won the national match in the past 2 years as the subjects. A high speed camera (120Hz) was used to shoot their movements, which is quantified by a Silicon Coach at the same time. Based on the experimental result, the DKA can be a long, short, or rapid jumping attack movement, whose vertical displacement is large and the rolling angle of the body in the air is large. Therefore, it is suitable for the combo attack after the active attack in the competition

The relationship between velocity utilization rate and pole vault performance

In the pole vault event, the velocity of approach is a highly vital factor. As velocity of approach improvements highly impact performance improvements. This study analysed the relationships between sprint running’s speed (SR), pole running (PR, without jump), and the pole vault approach (PVA, with real jump). Analysed too were the relationships between both the approach and performance’s respective running distance, velocity, and velocity utilization rates. Methods: Ten male pole vaulters were recruited. Measured was each 5-meter segment’s average velocity of his respective SR, PR, and PVA, along with the distance to maximum velocity. Results: The maximum average velocity of the PR’s 5m segments altogether was significantly positively correlated with pole vault (PV) performance; The maximum average velocity of the PR’s 5m segments altogether was significantly positively correlated with the last 5m PVA average velocity; The PVA velocity’s utilization rate was significantly negatively correlated with the difference between the distance to the PR’s maximum velocity and the PVA’s distance. Conclusion: The PR segment’s maximum speed capability can evaluate both a pole vaulter’s potential and pole vault-specific abilities. This study’s recruited pole vaulters’ respective approach distances were generally insufficient that resulted in a lower velocity utilization rate. Suggested is that in training, the pole vaulter could first find the distance required to reach the highest velocity upon starting from the PR test. Thus, this subsequently known distance could be applied in tandem with the pole vault’s approach to both improve the PVA’s utilization rate and reach the individual highest speed level