Effect of aspect ratio on the flow around finite circular cylinder in the critical regime

Abstract

This study aims on the aerodynamic characteristics of flow around finite circular cylinder at critical Reynolds number Four different cylinder models are tested in the low speed wind tunnel Their aspect ratios are 1 2 3 and 4 Concerned with the effects due to the configuration of the finite circular cylinder the flow phenomenon observed could be categorized into three regions namely the free end at the upper level of the model the middle level where the flow can be regarded as passing over an uniform circular cylinder and the lower level where the flow is constricted by the junction of the cylinder model and the ground floor At each level the pressure signals of ±90^° and 180^° on the surface of models are measured The instantaneous flow characteristics in the critical transition range can be discussed with the real-time C_(?P±90?^° ) and C_pb data Also the drag coefficient and the lift coefficient at critical Reynolds number of each finite cylinder are measured by a two-dimensional force balance From the experimental result drag crisis phenomenon can be observed when the aspect ratio of the model is from 2 to 4 When the model’s aspect ratio comes to 1 the drag crisis phenomenon doesn’t occur The instantaneous flow characteristics in the critical transition range can be discussed with the real-time C_L and C_D data Furthermore oil-film visualization method is applied The oil film is prepared with the mixture of paraffin oil and TiO2 powder and is applied on the model surface The aspect ratio of the model in this test is 4 and 1 Discussion on the flow visualization results are focus on the effect due to the configuration of the finite circular cylinder and the unsteadiness of laminar separation bubble(s) to the aerodynamic flow around the finite circular cylinder model

Date of Award	2020
Original language	English
Supervisor	Jiun-Jih Miau (Supervisor)