The steady-state response and breathing mechanism of a cracked rotor supported by flexible bearings are investigated in this paper. The generalized and efficient method proposed in this paper can be used to study the dynamics of complicated cracked structures without much modification. First, a three-dimensional finite element model of the cracked rotor-bearing system is established in the rotating frame and a general contact model for modeling the breathing crack is proposed. A component mode synthesis is used to form a reduced-order model. Then, a procedure combining multi-harmonic balance method with arc-length method is used to search the response solution. To accelerate the calculation, the analytical formulations for calculating the tangent stiffness matrix are used. Finally, the gravity induced response and breathing mechanism of a cracked rotor-bearing system are obtained. Interesting result is that the rotational speed and the crack depth will influence the breathing mechanism even if the load remains unchanged.
The effect of non-sinusoidal motion which influences the energy extraction performance of foil is considered in this paper. Two oscillation motions, the combined non-sinusoidal plunging and sinusoidal pitching motion, as well as the combined non-sinusoidal pitching and sinusoidal plunging motion, are selected to investigate the oscillation process of two-dimensional parallel foils numerically. The optimal oscillation motion and average power coefficient at different combined motions are gained. The effects of the plunging motion and pitching motion at different oscillation motions are analyzed, and the evolution law of the foil lift force and vortex field are obtained. It is indicated that the non-sinusoidal motion has a significant influence on energy extraction. When the motion is combined (non-sinusoidal plunging and sinusoidal pitching motion), the best extraction performance is gained at K h = −0.5. The maximal C Pm is 0.375 and the maximal η is 0.188. When the motion is combined (non-sinusoidal pitching and sinusoidal plunging motion), the maximal C Pm is 0.623 and the maximal η is 0.312 which appear at K θ = 2. For the same frequency, the more the plunging motion is similar to the sinusoidal motion, the more energy is extracted by foils. While the more the pitching motion approximates to the square wave, the worse the achieved extraction performance is.
In order to adapt to the high-efficiency and low-resistance performances required by the new generation of gas turbine, a new type of two-pass rectangular channel with cross bridge and oval-shaped dimple structure is proposed for internal cooling of blade mid chord region. Firstly, the flow structure, heat transfer and friction characteristics of the novel channels under stationary and rotating conditions are numerically analyzed and compared in detail. Then the effects of cross bridge type/layout and dimple dimension/arrangement on the cooling performance are discussed. And the coupling mechanism of cross bridge, turning bend, oval-shaped dimple and rotation effect is revealed. The results show that the introduction of the cross bridge enables the coolant flow into the second pass in a distributed manner, which weakens the flow aggregation and extrusion in the tip turning bend region, thus the flow structure is optimized. Although the heat transfer is slightly weakened, the friction factor is reduced by 66.3% and 51.4%, and the overall thermal performance is improved by 16.7% and 11.6% (different cases) at most, for stationary and rotating conditions, respectively. The oval-shaped dimple achieves local heat transfer enhancement by controlling flow separation and reattachment. Furthermore, the optimized cross bridge type/layout and dimple dimension/arrangement are also obtained. This research will provide important reference data for the development of high-efficiency mid chord cooling technology for gas turbine blade.
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