Bioreactors are used as cell culture systems for growth and maintenance of tissue-engineered scaffolds that serve as three-dimensional (3D) templates for initial cell attachment and subsequent tissue formation. The bioreactors' fluid dynamic environment is known to play a crucial role in the synthesis of cellular components via flow-mediated mechanical stimuli. Computational fluid dynamics (CFD) models in the slow turning lateral vessel (STLV Synthecon, Inc.) were simulated under Couette flow conditions. Systematic research of the wall shear stress (WSS) effects on the scaffold's geometry has been limited. Therefore, direct qualitative and quantitative correlations for WSS values were performed by analyzing and comparing WSS value distributions of two scaffold shapes. Under experimental flow conditions, the disc and prolate spheroid shapes exhibited dissimilar WSS distribution. Nonetheless, when compared to the disc models, the high pressure stagnation region of the spheroid was reduced between 60% and 95%. In the spheroid shape, approximately 40% increase in the shear stress surface exposure to flow ranged from 2 to 3 dyn/cm(2). These values suggest that WSSs are likely affected by scaffold shape and vary little with location within the Synthecon STLV. The proposed simulation studies evidenced the CFD model's flexibility to characterize and quantify forces affecting tissue-engineered scaffold design.
In this study, the aerodynamic performance of a thick airfoil is analysed, after installing leading-edge roughness to emulate a severe state on the airfoil surface. The impact on aerodynamic coefficients has been quantified using two roughness methods: zig-zag tape and sandpaper. Wind tunnel tests are carried out at a Reynolds number of 3•106. At low angles of attack, zig-zag tape and sandpaper provide comparable lift and drag coefficients but significant variations of these coefficients are obtained for high angles of attack. Stalled flow is the cause of the most significant variation on the airfoil performance between smooth and rough surface states. Vortex generators are adapted to recover the lift coefficient value previously given by the airfoil under smooth conditions. As a result, vortex generators are able to reduce the loss of lift and the sensitivity of the airfoil to the rough state.
The mid-span region of wind turbine blades can be thickened to fulfil the structural requirements of the blade. Hence, thick airfoils, that were designed to operate at the root region of the blade, are moved to the mid-span region. This could not imply remarkable variations of the blade performance once its surface is smooth. However, the sensitivity of thick airfoils to roughness could cause significant aerodynamic impacts such as flow separation. This research aims to quantify the impact of the blade thickness, under smooth and rough conditions, in the annual energy production and the fatigue loads of the blade. Ten blade designs, linearly interpolated in thickness, are studied employing aero-elastic computations. The results reveal that the thickest blade increases the annual energy production by 5% with respect to the thinnest blade under rough conditions. Whereas this increase is less than 1% under smooth conditions. The loss of annual energy production varies with the blade thickness linearly for thin blades while it varies exponentially for thick blades up to 22%. Fatigue loads assessment confirmed a reduction of the damage equivalent load under smooth conditions, whereas the thickest blade increased it 28% under rough conditions.
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