本研究應用計算流體力學設計並分析雙心室輔助器(Bi-Ventricular Assist Device)電動液壓驅動器(Electro-hydraulic Driver)之內部流場，藉由電腦輔助設計軟體CATIA設計流道，進而使用計算流體力學分析軟體FLUENT分析流場，探討葉輪及流道損失，以達設計目標。離心式電動液壓驅動器藉由扭力馬達帶動離心式葉輪(Centrifugal Impeller)產生局部低壓，將工作流體從入口吸入，再經葉輪作功提高揚程後由旋轉套筒內負責收集流體的渦殼(Volute)流道收集，流體經由此面積漸擴的流道會減速增壓，並推動血泵(Blood Pump)以克服降主動脈端約120mmHg以上之背壓。本研究主旨是在嚴格空間限制下設計驅動器之內部流道，以期降低內部阻力及壓損，並提升系統效率達到設計目標。設計之次系統組件包括離心式葉輪、渦殼、入口流道和外殼流道，最後再模擬整個驅動器系統並探討其總體效能。離心式葉輪是根據工業用泵之經驗公式作初步設計，由角動量守恆、尤拉方程式和速度三角形設計葉片的入、出口角，進而得到三維的葉輪幾何外型，再使用計算流體力學作細部設計，探討細部流場如葉尖間隙(Tip Clearance)及邊界層效應的影響。渦殼設計主要探討剖面外型、出入口面積比、出口角度和舌尖(Tongue)外形倒角對泵浦的影響。葉輪入口流道是影響整個泵浦性能的關鍵，模擬結果發現由於不對稱的幾何外形會在入口流道誘導出一前渦漩(Preswirl)，且流場為完全非定常流場(Unsteady)，導致實際流場十分複雜，入口角度不再是初步設計角度，因而產生葉片失速的現象，並降低泵浦效率。在得到每一組件的部件設計後，結合整個系統進行總體模擬並分析其效能。研究發現葉輪初步設計所擬定的200mmHg揚程無法在克服流道損失後達到整體驅動器系統揚程120mmHg以上的要求，因此本研究提出兩項符合雙心室輔助器需求之電動液壓驅動器設計方案：一為直徑30mm之離心式葉輪以7500rpm之轉速操作，或直徑40mm以轉速5500rpm操作之設計皆可達到系統揚程120mmHg、流量24L/min之需求。然而這兩款改進後的設計其效率最高僅能達到14%左右，經流場分析發現此低效率肇因於邊界層效應及脈動式設計流體衝擊旋轉套筒而產生巨大的損失所造成。設計中並發現改善葉輪入口流場均勻性及出口流道高度可以有效地改進系統揚程。

Computational Fluid Dynamics (CFD) is used presently to design and analyze a centrifugal electro-hydraulic (EH) driver flow for the implantable Bi-Ventricular Assist Device (Bi-VAD). The internal flow passage was designed using computer-aided design (CAD) tool CATIA. Commercial CFD code FLUENT was employed to analyze the flowfield and to improve the driver design. The motor-driven centrifugal impeller generates a local low pressure region in the EH driver, causing flow sucked into the impeller eye by climbing through the gap between the driver housing and the dome valve surface. The impeller-pressurized fluid is collected by a volute embedded in the dome valve body. Diffusion in the volute further converts the flow kinetic energy into static pressure so as to match the back pressure (~120mmHg) in the aortic side. The objective of the present work is to design an internal flow passage that can minimize the system loss and improve the driver efficiency. Design and flow analysis of subsystems including centrifugal impeller, volute, system internal flow passages as well as the whole model simulation were carried out. Preliminary impeller configuration was designed using empirical formula to determine the inflow and outflow angles and other related geometric parameters. CAD model was configured based on the CATIA platform, which was then used for subsequent CFD flow analyses. Volute design parameters studied consist of volute profile, volute outlet-inlet area ratio, volute outlet angle and tongue geometry. The impeller inlet duct design holds a central position in designing a high-performance EH driver. Simulation results show that asymmetric flow passage geometry induces preswirl around the impeller entrance. This non-uniform inlet flow causes flow separations in impeller and thus reduces the pump efficiency. The initial design concludes that the internal system loss is larger than the work input exerted by the centrifugal impeller, making the pressure delivered in the aortic side less than the required 120mmHg. Design objective is then modified with elevated total pressure rise specified across the impeller blades. Either speeding up the original impeller rotational speed to 7500rpm or enlarging the impeller diameter to 40mm, but with a slower rotational speed of 5500rpm, can achieve the design goal of delivering 24L/min flowrate to the aorta. It was found in the design modification that boundary layer effects and the inflow impinging on dome valve wall may result in low overall system efficiency around 14%. Moreover, either improving the inlet flow uniformity around impeller eye or enlarging the exit channel height around the impeller outlet could be effective strategy in improving the whole system overall performance.

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