Rotational speed

About: Rotational speed is a research topic. Over the lifetime, 23327 publications have been published within this topic receiving 151696 citations. The topic is also known as: speed of revolution & revolution rate.

Experimental Investigations on Upper Part Load Vortex Rope Pressure Fluctuations in Francis Turbine Draft Tube

Abstract: The swirling flow developing in Francis turbine draft tube under part load operation leads to pressure fluctuations usually in the range of 02 to 04 times the runner rotational frequency resulting from the so-called vortex breakdown For low cavitation number, the flow features a cavitation vortex rope animated with precession motion Under given conditions, these pressure fluctuations may lead to undesirable pressure fluctuations in the entire hydraulic system and also produce active power oscillations For the upper part load range, between 07 and 085 times the best efficiency discharge, pressure fluctuations may appear in a higher frequency range of 2 to 4 times the runner rotational speed and feature modulations with vortex rope precession It has been pointed out that for this particular operating point, the vortex rope features elliptical cross section and is animated of a self-rotation This paper presents an experimental investigation focusing on this peculiar phenomenon, defined as the upper part load vortex rope The experimental investigation is carried out on a high specific speed Francis turbine scale model installed on a test rig of the EPFL Laboratory for Hydraulic Machines The selected operating point corresponds to a discharge of 083 times the best efficiency discharge Observations of the cavitation vortex carried out with high speed camera have been recorded and synchronized with pressure fluctuations measurements at the draft tube cone First, the vortex rope self rotation frequency is evidenced and the related frequency is deduced Then, the influence of the sigma cavitation number on vortex rope shape and pressure fluctuations is presented The waterfall diagram of the pressure fluctuations evidences resonance effects with the hydraulic circuit The influence of outlet bubble cavitation and air injection is also investigated for low cavitation number The time evolution of the vortex rope volume is compared with pressure fluctuations time evolution using image processing Finally, the influence of the Froude number on the vortex rope shape and the associated pressure fluctuations is analyzed by varying the rotational speed

Propulsion control using steering angle and vehicle speed to determine tolerance range

Abstract: A propulsion control system for motor vehicles for maintaining stable driving conditions, having a computer unit for determining a desired value or a tolerance range for the rotational speed difference of the front wheels or of the lateral acceleration or of the yaw velocity, and having a comparator unit in which this desired value or tolerance range is compared with the measured actual value, in which case the difference between the actual value of the desired value or tolerance range is used as a control signal for the brakes of the wheels and/or for a power control element of the vehicle engine.

Turbofan engine including fans with reduced speed

Abstract: An impeller is directly driven by an output shaft of a core engine. The airflow produced by the impeller rotates an air turbine and a fan disposed integrally with the air turbine. The impeller and the air turbine form a fluid coupling which serves also as a speed reducing mechanism. The rotational speed of the fan can be reduced to be lower than that of the output shaft while retaining efficiency of the core engine. The outer diameter of the fan can be increased, raising a bypass ratio.