Novel Computational Fluid Dynamics Technique for Incompressible Flow and Flow Path Design of a Novel Centrifugal Compressor PDF Download

Author: Shashank Mishra
Publisher:
ISBN:
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Languages : en
Pages : 149

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Book Description
The incompressible flow equations are function of the pressure gradients and not the pressure. The most important issue in solution of flow equations of incompressible fluid is the pressure gradient vector which is appearing as a source term in the momentum equation, but does not have any obvious equation coupling it with other dependent variables. Accurate numerical solutions are obtained for the incompressible Navier Stokes equations in primitive variables. Explicit finite difference scheme computer code is developed to solve incompressible flow equations. In this study, consistent with the physics of incompressible flows, the velocity and pressure gradient vectors are considered as the dependent variables. In this case, that satisfies continuity equation to machine zero, the pressure gradient vector increases the number of dependent variables which requires additional equations to close the system of governing equations. Additional equations are obtained by reformulating the continuity equation and adding a time derivative term for the pressure gradient. Upon, convergence of the numerical solution, the continuity equation will be satisfied to an arbitrary constant. To enforce that constant to be zero, the continuity equation is set to be zero on the boundary of the solution domain. It is important to note that the curl of the reformulated continuity equation automatically satisfies the curl of the pressure gradient identity. This scheme is applicable for two and three dimensions, inviscid and viscous flows. Multistage axial compressor has an advantage of lower stage loading as compared to a single stage. Several stages with low pressure ratio are linked together which allows for multiplication of pressure to generate high pressure ratio in an axial compressor. Since each stage has low pressure ratio they operate at a higher efficiency and the efficiency of multi-stage axial compressor as a whole is very high. Although, single stage centrifugal compressor has higher pressure ratio compared with an axial compressor but multistage centrifugal compressors are not as efficient because the flow has to be turned from radial at outlet to axial at inlet for each stage. The present study explores the advantages of extending the axial compressor efficient flow path that consist of rotor stator stages to the centrifugal compressor stage. In this invention, two rotating rows of blades are mounted on the same impeller disk, separated by a stator blade row attached to the casing. A certain amount of turning can be achieved through a single stage centrifugal compressor before flow starts separating, thus dividing it into multiple stages would be advantageous as it would allow for more flow turning. Flow characteristics of the novel multistage design are compared with a single stage centrifugal compressor. The flow path of the baseline and multi-stage compressor are created using 3DBGB tool and DAKOTA is used to optimize the performance of baseline as well novel design. The optimization techniques used are Genetic algorithm followed by Numerical Gradient method. The multi-stage compressor is more efficient with a higher pressure ratio compared with the base line design for the same work input and initial conditions.