Imprinted Effusion Modeling and Dynamic CD Calculation in Gas Turbine Combustors

Abstract

A practical computational fluid dynamics (CFD) approach to modeling effusion orifices in gas turbine combustor liners is proposed specifically when liner metal geometry is not included and conjugate heat transfer is not invoked. The focus is on eliminating effusion orifices from the model while maintaining the imprint of the orifices on the cold and hot sides of the liner wall. The imprinted boundaries serve as embedded mass flow inlets and outlets on both sides of the wall and maintain the integrity of the wall geometry. An empirical model is then used to extract and inject mass from the cold and hot sides of the liner, respectively. The mass extraction and injection process is performed for each orifice based on local conditions such as pressure, temperature and discharge coefficient. The discharge coefficient is, in turn, dynamically computed for each orifice based on approach angle, approach Mach number, discharge Mach number and orifice length to diameter ratio. With this approach, the fidelity of the liner wall is preserved for better heat transfer predictions and easier near wall meshing. In addition, the discharge coefficient is not assumed but calculated allowing the redeployment of inherently inadequate effusion orifice mesh cells to other critical areas of the combustor. Presented are results of two combustor cases to demonstrate the practicality and accuracy of the proposed method as compared to standard effusion modeling and their comparison with rig data.

Application of an Aerothermal Model for Effusion Cooling Systems and Finite Rate Chemistry in Aero-Engine Combustors

“…Thus, the flow as well as the convective heat transfer inside the tube have to be modelled. For the flow an one dimensional momentum conservation equation based on a simple streamline theory can be used [3], [4]. The velocity at the hole exit is then calculated from pressure drop over the holes as follows…”

“…Furthermore the results of an investigation of the influence of the grid size have been presented. In the work of Rida et al (2012) [4] the authors reported an alternative method to the addition of source terms, hence represented by imprinted effusion modelling which consists in defining cold and hot sides of the effusion orifice with outlet and inlet boundary conditions but at adiabatic conditions only. The mass flow rate is calculated locally starting from the pressure drop and a correlation-based calculation of a discharge coefficient c D .…”

“…The mass flow rate is calculated locally starting from the pressure drop and a correlation-based calculation of a discharge coefficient c D . The main goal of our work is the usage of the boundary method compared to [4] with a forced mass flow assumption determined by the pressure drop over the hole in a detailed simulation. The boundary pattern of each virtual hole is mapped as good as possible to obtain the real hole cross section.…”

A Thickened-Hole Model for Large Eddy Simulations over Multiperforated Liners

“…The first one, less expensive, leads to average solutions when the second gives access to instantaneous solutions and thus, better predicts the mixing and the turbulence flame interaction, which is more desirable in combustor simulations. To represent the liners, various modelling strategies have been used in the literature [13][14][15][16][17][18]. To distinguish these models and relate them to corresponding mesh resolution constraints, it is useful to introduce the aperture-to-mesh ratio:…”

Local Source Based CFD Modeling of Effusion Cooling Holes: Validation and Application to an Actual Combustor Test Case

“…Another innovative solution was developed by Rida et al [11], which reported that up to a million cells is required for a single hole to reach the mesh independence for an accurate prediction of the flow structures within the perforation. According to the authors, a feasible method, alternative to the addition of source terms, is hence represented by imprinted effusion modeling, which consists in coupling cold and hot sides of the effusion orifice with an outlet and inlet boundary condition, without meshing the hole.…”