Amir Nejat

This study carries out computational aeroacoustic calculations around the tip region of the CART II wind turbine blade. Additionally, two modified tip designs, namely; tip O and tip R, are further investigated to determine how the geometry of the tip region affects the noise emission characteristics of the wind turbine. The study focuses on the tip vortex noise mechanism using hybrid computational aeroacoustic to tackle the issue of the enormous computational power required for direct noise simulation. Improved Delayed Detached Eddy Simulation (IDDES) technique is used to calculate the instantaneous turbulent flow field near the sound source region, and the noise prediction in far-field is performed using the Ffowcs Williams and Hawking’s (FW-H) acoustic analogy. The method visualizes the flow field near the blades’ tip, assisting researchers to have an accurate understanding of aerodynamically induced noise mechanisms in that highly complex flow region, thus being able to modify tip design in a way that contributes to lower overall noise emission. The results for the outboard section of the CART II wind turbine’s blade are validated with experimental data. Broadband noise sources such as turbulent-boundary-layer trailing-edge (TBL-TE) noise and the tip vortex noise mechanisms are investigated for the base case as well as tip O and tip R. The results show that the overall sound pressure level (OASPL) and the generated torque of tip R and tip O, are 2.0 %, 5.0 % and 0.8 %, 2.2 % lower than the base case, respectively.

Acute ischemic stroke (AIS) is the leading cause of mortality and disability worldwide. AIS occur while cerebral arteries become blocked by embolism or thrombosis. Aspiration thrombectomy is a promising interventional device to extract massive clots from occluded cerebral arteries. The aim of this article is to develop a computer‐aided method to clarify the performance of aspiration catheter and identify the risks of aspiration for each specific AIS patient. In order to simulate the aspiration process, a three‐dimensional fluid‐structure interaction (FSI) method was developed. The blood clot was modeled as a porous media which composed of viscoelastic fibrin networks. The finite element method (FEM) was implemented to compute the blood flow dynamics in the simplified cerebral vessel. The introduced clot model was validated by comparing the numerical results with experimental data. Furthermore, the analytical solution of the flow through the partially porous pipe was considered to validate FEM. In this research, the performance of two model of the Penumbra aspiration catheter—4MAX and 5MAX—were were compared at three distinct suction pressures. The aspiration ratio of the clot, aspiration time, amount of free fragments, wall shear stress (WSS), and extracted volume of the blood were calculated to evaluate catheters performance. At suction pressure −50 kPa, the aspiration ratio of 5MAX catheter reached 86.58% within 1.36 s. However, in 4MAX case, aspiration ratio of 76.41% was achieved within 1.39. Also, 5MAX catheter created 6.11% fewer free fragments in comparison to 4MAX. Hence, the possibility of distal embolization of 4MAX model was greater. However, the risk of vessel wall rupture was higher in 5MAX by considering mean WSS.

A centrifugal blood pump is a common type of pump used as a left ventricular assist device in the medical industries. Therefore, the improvement of the device bio-compatibility to reduce the blood damage and to increase the efficiency has become a major challenge. In the current work, a metamodel-assisted genetic algorithm is employed to simultaneously optimize the impeller and volute geometries of a typical centrifugal blood pump. The overall shape of the base design is inspired from HeartMate3 LVAD, and the main dimensions of the base design including inlet and outlet radius, blade angle distribution, volute cross-section area distribution, etc., are designed in our laboratory. Three different scenarios are investigated using three different objective functions, i.e., (1) hydraulic efficiency, (2) pressure head, and (3) hemolysis index (HI). The results showed that the shape optimized by pump efficiency has also nearly the same level of HI as the shape optimized by HI. Hence, to reduce computation time, one can use efficiency instead of HI as an objective function. However, one must check the HI level after such optimization to see whether it is within the acceptable range of HI for such bio application.

A centrifugal blood pump is a common type of the pump used as a left ventricular assist device (LVAD) in the medical industries. The reduction of the LVADs hemolysis level to reduce the blood damage is one of the major concerns in designing of such devices. Also, the enhancement of the LVADs efficiency to decrease the battery size is another design requirement. The blood damage critically depends on the state of the blood being pumped. Besides the blood state, the blood damage also depends on the pump impeller and volute geometries. In this research, a multi‐objective optimization of a centrifugal blood pump is performed. A complete 3D‐optimization platform is established for both impeller and volute of a centrifugal blood pump consisting of parametric modeling, automatic mesh generation, computational fluid dynamics (CFD) simulation, and optimization strategy. A vast number of cases with various impeller and volute shapes are numerically simulated. Three different metamodels are created using artificial neural networks (ANNs) in order to approximate the pump hydraulic efficiency, hemolysis index (HI), and pressure head. The inverse of the relative pressure head is defined as the first objective and the summation of relative hemolysis index and the inverse of the relative efficiency is assumed as the second objective. Non‐dominated Sorting Genetic Algorithm‐II (NSGA‐II) is used to find the Pareto Front. A set of optimal points is selected. Finally, for the physiological flow conditions, the optimum design that provides 11.9% HI reduction and 7.2% efficiency enhancement is selected.

One important safety issue in automotive industry is the efficient cooling of brake system. This research work aims to introduce an optimized cooling vane geometry to enhance heat removal performance of ventilated brake disks. The novel idea of using airfoil vanes is followed as the basis of this investigation (Nejat et al., 2011, “Heat Transfer Enhancement in Ventilated Brake Disk Using Double Airfoil Vanes,” ASME J. Therm. Sci. Eng. Appl., 3(4), p. 045001). In order to perform the optimization technique efficiently, an integrated shape optimization process is designed. According to the aerodynamic and heat transfer considerations, first an appropriate airfoil is selected as the base profile to be optimized. For the shape modification purpose, a curve parameterization method named class shape transformation (CST) is utilized. The control parameters defined in CST method are then established as the geometrical design variables of an improved territorial particle swarm optimization (TPSO) algorithm. In order to overcome the potential bottleneck of high computational cost associated with the required computational fluid dynamics (CFD)-based function evaluations, TPSO algorithm is coupled with a predictive artificial neural networks (ANN), well trained with an input dataset designed based on the Taguchi method. The obtained profile shows an evident convective heat dissipation improvement accomplished mainly via airflow acceleration over the vanes, avoiding early flow detachment and adjusting the flow separation region at the rear part of the suction sides. The results also reveal the approaches by which such a superior performance is achieved by means of the modified surface curvatures.

An electromagnetic actuated micropump with flexible sequence of valves is presented and investigated in the present article. Two flexible valves are placed inside the microchannel in order to bidirectionalize flow, employing the idea of rectifying mechanism of lymphangion in the lymphatic transport system. A time-dependent magnetic field exerts force on the soft magnetorheological elastomer (SMRE) wall, and therefore, the enclosed fluid is forced to move. The valve series are embedded in such a way that prevent flow from leaving the left terminal, and stop fluid flow entering from the right terminal. Therefore some fluid move left to right, which is called V _Net . The net volume is considered as the target design for the performance of the micropump. A fully coupled time-dependent magneto-fluid–solid interaction (MFSI) simulation of two-dimensional incompressible fluid flow is conducted. The finite element method is used to solve all physics involved. Simulation results indicate capability of the proposed mechanism to propel fluid in one direction. A parametric study is performed to investigate the effect of key geometric, magnetic, and structural parameters on the net transported volume. Results show that under optimum conditions the micropump is able to transmit a net volume of fluid nearly two times more than the basic design. The final model is able to pump 0.055 ( μ l) of water (at 25 °C) in 1 s. The proposed micropump can operate in a wide range of applications, such as artificial organs, organ-on-chip, and aerospace applications.