Browsing by Author "Cheng, HP"

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Analysis of the flow in the grooves of a molecular pump
(2001-07-01)
Tsui, YY
;
Kung, CP
;
Cheng, HP
;
機械工程學系
;
Department of Mechanical Engineering
A computational procedure used to solve conservation equations governing the slip flow in a molecular pump of the Holweck type is developed, The finite volume method is used for discretization and the gr id is arranged in the curvilinear, nonstaggered form The slip boundary condition is imposed on the solid walls. The clearance gap between the rotor and the casing is ignored It is evident fi um the calculation that the pressure difference between the two side walls of the channel, iel med pressure side and suction sick, varies in accordance with the pressure difference between the inlet and the outlet of the pump, Thus, the side-wall pressure difference can play. the role of an indicator of pumping effectiveness, Tests on a variety. of configurations show that to achieve the best performance both the spiral angle and the channel height need to be optimized, Besides, it is better to have fewer flow channels and to place these channels on the rotor instead of on the casing.
Tumbling/squish interaction in loop-scavenged two-stroke engines
(1997-12-01)
Tsui, YY
;
Cheng, HP
;
機械工程學系
;
Department of Mechanical Engineering
This article describes a numerical investigation of the flow in a loop-scavenged two-stroke engine equipped with a head-bowl combustion chamber. The bowl is either placed in the center of the cylinder head or displaced away from the center. Attention is focused on the period of compression and early expansion. Results show that the effects of compression of the tumbling vortex by the piston become prominent after the midcompression stage, resulting in significant cascading of energy from mean flow to turbulence, followed by a fast decay of turbulence. The subsequent emergence of squish and reverse squish helps retard die decay. As a consequence, the cases with head bowls possess higher levels of mean flow and turbulence than those without bowls at top dead center and the later stage. It is also shown in the results that the offset of the head bowl has significant effects on the mean flow and turbulence characteristics, highly dependent on the offset direction.