Glenn Ht Bem Conjugate Heat Transfer Solver For Large Scale Turbomachinery Models

Author : Robert Knapke
Publisher :
ISBN 13 :
Total Pages : 242 pages
Book Rating : 4.:/5 (927 download)

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Download or read book High-Order Unsteady Heat Transfer with the Harmonic Balance Method written by Robert Knapke and published by . This book was released on 2015 with total page 242 pages. Available in PDF, EPUB and Kindle. Book excerpt: Despite the significant advancements in computational fluid dynamics, modeling turbomachinery flows remains extremely difficult. The challenges include complex unsteady blade row interactions, large thermal gradients, and complex geometries. During the design process, simplifications and approximations are necessary to reduce the computational cost. Two common simplifications are the use of adiabatic boundary conditions and steady methods for resolving the flow field in multistage turbomachinery. The Harmonic Balance (HB) method is an efficient way to simulate periodic unsteady phenomena. Compared to traditional time-marching methods, the HB method reduces the computational cost by considering only the dominant frequencies of the solution field. Using a Fourier series representation of the solution variables, an unsteady governing equation transforms into a series of steady-like equations. The cost is further reduced when considering multistage turbomachinery. Unlike a time-marching method, which requires periodic boundaries, the HB method models a single blade passage per blade row. A phase lag condition is applied instead of a periodic condition. At the junction between blade rows, an interface resolves the relative motion and any passage mismatch. Assuming the heat transfer of wall boundary conditions is, by definition, non-physical. Assuming no heat transfer (an adiabatic wall) is certainly wrong for turbomachinery flows because of the large thermal gradients. An constant temperature wall can provide a better approximation, but for complex geometries, the temperature is not known a priori. The most accurate approach involves modeling both the fluid and solid domains, which is called Conjugate Heat Transfer (CHT). This can be performed in several ways, but the most stable method is one in which the fluid and solid are strongly coupled. This strong coupling is achieved by using the same discretization in both domains. This dissertation details an approach for accurately and efficiently simulating the unsteady heat transfer in turbomachinery flows. The HB and CHT methods are developed within a framework that uses a high-order Discontinuous Galerkin (DG) spatial discretization and a versatile Chimera overset scheme. The implemented HB method is fully linearized, allowing the use of an efficient Quasi-Newton solver. The HB equations are coupled within a linear system that includes the linearized HB pseudo-spectral operator. Phase lag and relative motion interfaces are included, hence the computational domain of multistage turbomachinery simulations is reduced to one passage per blade row. Modeling turbulent flows is achieved with the Spalart-Allmaras turbulence model. A strongly coupled CHT method is introduced. The solid and fluid domains are both discretized with the DG method. The fluid to solid interface enforces a consistent wall temperature and heat flux. The Harmonic Balance method, the Conjugate Heat Transfer method, and the Spalart-Allmaras turbulence model are independently verified using a series of test cases. In addition, CHT on curved 3D geometries is performed for the first time. Lastly, unsteady heat transfer is simulated using the combination of the HB and CHT methods. These test cases demonstrate the fast convergence and accurate modeling of the implemented methods. This work provides the basis for the accurate and efficient simulation of turbomachinery flows.