This paper presents a novel one-dimensional design method based on the radial equilibrium theory and constant span-wise diffusion factor to redesign of NASA rotor 67 just aerodynamically with a higher pressure ratio at the same design point. A one-dimensional design code is developed to obtain the meridional plane and blade to blade geometry of rotor to reach the three-dimensional view of rotor blades. To verify the redesigned rotor, its flow numerical simulation is carried out to compute its performance curve. The experimental performance curve of NASA rotor 67 is used for validation of the numerical results. Structured mesh with finer grids near walls is used to capture flow field and boundary layer effects. RANS equations are solved by finite volume method for rotating zones and stationary zones. The numerical results of the new rotor show about 9% increase in its pressure ratio at both design and off design mass flow rate. The new rotor has a higher outlet velocity through its upper span improving bypass ratio of a turbofan engine. To prove the new fan ability of producing more bypass ratio, a thermodynamic analysis is conducted. The results of this analysis show 13% increase in bypass ratio and 5.7% decline in specific fuel consumption in comparison to NASA rotor 67.
In this study, a new inverse design method called Elastic Surface Algorithm (ESA) is developed and enhanced for axial-flow compressor blade design in subsonic and transonic flow regimes with separation. ESA is a physically based iterative inverse design method that uses a 2D flow analysis code to estimate the pressure distribution on the solid structure, i.e. airfoil, and a 2D solid beam finite element code to calculate the deflections due to the difference between the calculated and target pressure distributions. In order to enhance the ESA, the wall shear stress distribution, besides pressure distribution, is applied to deflect the shape of the airfoil. The enhanced method is validated through the inverse design of the rotor blade of the first stage of an axial-flow compressor in transonic viscous flow regime. In addition, some design examples are presented to prove the effectiveness and robustness of the method. The results of this study show that the enhanced Elastic Surface Algorithm is an effective inverse design method in flow regimes with separation and normal shock.
In the present study, the performance of a centrifugal compressor is improved by replacing the combination of vaned radial diffuser and axisymmetric vaneless 90-degree bend by a vaned 90-degree bent diffuser. It controls the outlet flow angle and reduces the overall diameter of the compressor. The optimum number of guide vanes inside the 90-degree bent diffuser is obtained using 3-D numerical simulation. Indeed, changing flow direction simultaneous with decreasing flow velocity through the 90-degree bent diffuser will increase the possibility of secondary flow and separation. Here, the meridional plane of the 90-degree bent diffuser is modified to reduce secondary flow and separation. Geometry modification process integrates Ball-Spine inverse design method as the shape modification algorithm and a quasi-3D analysis code as the flow solver. The current quasi-3D flow solver is in fact a 3-D flow solver that solves viscous flow between two virtual guide vanes located at a very close distance with free slip condition over them. In other words, in the current quasi-3D analysis, stream surfaces are the same as the virtual guide vanes and no slip condition is just applied on the hub and shroud. Shape modification process is carried out by improving the current hub and shroud pressure distribution and applying it to the inverse design algorithm. Spines directions are specified in a way that geometry would change only in the meriodional plane and guide vanes angle remain unchanged in the blade to blade plane through the geometry modification process. Having modified the meridional plane, the new vaned 90-degree bent diffuser is examined by the 3-D flow solver. Results show not only the secondary flow is reduced in the new 90-degree bent diffuser, but also its efficiency increases up to 2%. On the other hand, the overall diameter of the compressor decreases about 24%.
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