Arterial bypass graft operations are frequently carried out to treat narrowed arteries by directly creating a detour, or bypass, around a section of the artery that is blocked. A graft can be a portion of the patient's healthier veins or arteries or a synthetic tube that the surgeon connects above and below a blockage to allow blood to pass through it and around the blockage. Bypass grafting is a common technique to treat Coronary Artery and Peripheral Vascular Diseases. Synthetic grafts are also used to create an 'access point' for patients with diabetes or renal diseases who need haemodialysis treatment. One of the main concerns with using both natural and synthetic grafts is their failure due to thickening of the arterial walls (known as intimal hyperplasia), especially around the surgical connection between the grafts and veins/arteries. It is now widely accepted that haemodynamic factors (i.e. fluid dynamics of the blood) play an important role in the failure or success of the grafts. Therefore, the overall aim of the present project is to improve the patency of these grafts through developing a novel and optimised flow field augmentation device. This project seeks to design a novel vascular device which induces spiral flow in grafts, especially near the junctions. This work is motivated by the research which has shown that the spiral flow (which is caused by the rotational compressive pumping of the heart) is a natural phenomenon in the arterial system and helps to remove unfavourable flow environment such as turbulence, stagnation and oscillatory shear stress, which are the main causes of intimal hyperplasia at graft junctions. In order to fully understand the haemodynamic effects of the spiral flow and to obtain an optimum graft design, Computational Fluid Dynamics (CFD) technique is used as a modelling and simulation tool to run several numerical tests which can be conducted in a cost-effective manner. Once the role of the spiral flow in grafts was determined, shape optimisation analysis will be carried out to search for an optimal configuration for a novel vascular prosthesis design. Further analysis will be carried out to turn this idea into a viable prosthetic design. If successful, this design could significantly enhance the health and quality of life of patients requiring bypass grafts or haemodialysis including people suffering from heart and circulatory diseases and diabetes.