Novel interspersed windings to reduce space flux harmonics caused by fractional-slot of synchronous machine
Fractional-slot windings is widely used in synchronous machine due to give us more flexibility on selection of the number of slot at design stage. It is also known that fractional-slot windings produces additional harmonics compare to integral-slot windings. These harmonics may cause increasing of stray losses and stator core vibration This paper describes the result of space flux harmonics caused by fractional-slot windings and propose novel interspersed windings that reduces the even order and/or fractional number space flux harmonic components. The advantage of proposed winding was confirmed by using numerical analysis and experiment using model winding machine.
Special winding to reduce space flux harmonics caused by fractional-slot
It is known that fractional-slot winding produces different harmonics from integral-slot winding. The authors studied space flux harmonics caused by fractional-slot winding and proposed a new winding method that reduces the low order space flux harmonic components (special winding method based on intersperse one coil winding), The advantage of this proposed winding method was confirmed using a model winding.
Turbulent boundary layer wall‐pressure fluctuations downstream from an abrupt change in surface roughness
Spectra of wall‐pressure fluctuations beneath a turbulent boundary layer have been investigated immediately downstream from an abrupt change in surface roughness, from slightly rough to very rough. Over the measurable frequency band (400 Hz to 7 kHz), the spectra in the first 150 mm scale on wall variables. This indicates that the motions responsible for the pressure fluctuations measured in this region are very close to the wall. Farther downstream this scaling procedure breaks down. It is suggested that the initially thin internal layer behaves independently of the flow external to it until it has grown appreciably and only then interacts with the outer boundary layer. It was found that, for all frequencies measured, the dimensional spectral level decreases initially then rises to a maximum at 250 mm from the roughness change before decreasing once more. The position of the maximum is close to where the internal layer ceases to have a distinct edge.