## 1 Introduction  
Aortic valve diseases are estimated to affect more than 12 million people globally, and surgical aortic valve replacement (SAVR) is one of the primary management strategies among patients with severe conditions [1; 2; 3]. More than 200,000 SAVRs are performed annually worldwide [4].  
The stentless bioprosthetic aortic valves have been widely used in SAVR, which are not only advanced in terms of being free of anticoagulation after implantation, but also exhibit superior hemodynamics performances comparable to the native aortic valve [5; 6]. However, the implantation of stentless valves is technically more difficult [7]. Therefore, a stentless aortic valve prosthesis with an easy implantation technique is of great interest.  
The single-point attached commissure (SPAC) implantation technique, which sutures the commissure to the aortic wall at the level of the sinotubular junction (STJ) at only three single pointsand the base of the valve to the aortic root, greatly improved the efficiency of clinical implantation procedures [8]. The early generation of the SPAC technique was incorporated with simple tubular leaflet geometric design [9]. Based on this, [PERSON] et al. developed a novel SPAC molded prosthetic valve design [10], which incorporated the molded leaflet design from [PERSON] et al. [11]. The leaflet of the molded valve mimics the three-dimensional (3D) geometry of the native valve. Previous numerical, in vitro and in vivo animal studies have shown that the SPAC molded valve design has superior performance in terms of the structural dynamics, local hemodynamics and stress distribution [10; 12; 13].  
In addition to the valve performance, the aortic valve design also affects aortic hemodynamic characteristics. As a major artery that distributes the oxygenated blood to the circulatory system, the hemodynamic environment in the aorta have been reported to play critical roles in the maintaining of its health as well as functionality [14]. One of the most representative characteristics of the physiological aortic flow is the helical flow, which has been observed in several in silico, in vitro and in vivo studies [14; 15; 16; 17]. Among the healthy subjects, the presence of helical flow has been associated with optimized fluid transportation as well as the atheoprotective function of the arteries [14; 18]. However, several studies demonstrated that pathological conditions of the aortic valve, including bicuspid valves, SAVR and transcatheter aortic valve replacement (TAVR), could result in aberrant helical flow, eccentric flow impingement and subsequently alter the wall shear stress (WSS) distribution in the aorta [17; 19; 20; 21; 22; 23; 24]. Such changes in local flow environments have been identified as the major risk factors of platelet activation, valvular thrombosis aortic wall remodeling, aortic dissection, and aortic dilation [25; 26].  
Despite the fact that the hemodynamic impacts of several mechanical and bioprosthetic valves on aortic flow have been reported, the influences of the SPAC valve designs on the flow in aorta are still unclear. In light of this, a series of computational fluid dynamics (CFD) simulations were conducted in this pilot study to elucidate the influence of the SPAC molded design on the aortic hemodynamic environments. The flow pattern, WSS distribution, flow helicity and vorticity were compared between SPAC tubular, SPAC molded and conventional valves.