The interior flowfield analysis of fan has been considered to be one of the most difficult problems in the past. With the advent of computational fluid dynamics (CFD) methods, many flow problems inside the fan can now be solved with a good degree of accuracy. ¡@ A numerical study of the influence of inlet cone and volute cutoff on a centrifugal fan performance is presented in this work. Using the flow-visualization simulating analysis of the flow-flied characteristic of air across the inner of centrifugal fan, the performance curve with different inlet cone shape, inlet clearance gap, cone position, extending angle and curvature radius of cutoff arc were obtained and explored. The Reynolds-Averaged Navier- Stokes equations with the Standard k-£` turbulence model is used to simulate the three-dimensional, steady, incompressible, turbulent flow field inside a double-suction backward-curved centrifugal fan and is solved by control volume method. The numerical model is validated by experimental data. The results showed that (i) the inlet cone can induce the air to enter into the impeller smoothly and uniformly, which reduces the flow-separation occurrence along the blade surface. However, the inlet cone with larger friction loss will also slightly lessen the fan performance; (ii) recirculation zones appear inside the volute channel due to the existence of inlet clearance gap between inlet cone and volute, which results in part of fluid leaving from the impeller outlet re-entering into the impeller inlet and reducing the fan performance. This recirculation leakage ratio of fluid through inlet clearance gap increases with increasing inlet clearance gap, which is also depends on the shape of inlet cone; (ii) the distance of inlet cone extending into the impeller will interfere the uniformity of inlet airflow distribution along each blade height. The longer the extending distance, the larger the vortex zone occupying the inter-blade space which makes less fan performance; (iv) it makes only little improvement in the fan performance to change the shape of volute cutoff. ¡@ It is found that (1) decreasing the inlet clearance from 11mm to 5mm, the outlet average total pressure increases about 3.26%; (2) increasing the distance of inlet cone extending into the impeller from 0mm from 20mm, the outlet average total pressure decreases about 6.32%; (3)changing the shape of inlet cone, the outlet average total pressure increases up to 5.4%, and (4) reducing the tongue radius of volute cutoff from 25mm to 15mm, the performance efficiency of fan promotes slightly about 1%.

Approved for public release, distribution is unlimited / Methods used for designing the ramjet included conic shock tables; isentropic flow tables and the GASTURB code was used for aerothermodynamic performance prediction. The flow field through the proposed geometry was computed using the OVERFLOW code, and small modifications were made. Geometry and solid models were created and built using SolidWorks 3D solid modeling software. A prototype ramjet was manufactured with wind tunnel mounting struts capable of measuring axial force on the model. Shadowgraph photography was used in the Mach 4 supersonic wind tunnel at the Naval Postgraduate School's Turbopropulsion Laboratory to verify predicted shock placement, and surface flow visualization was obtained of the airflow from fuel injection ports on the inlet cone of the model. All indications are that the cold-flow tests were successful. / Ensign, United States Naval Reserve