Computational fluid dynamics (CFD) simulations are presented with an isothermal boundary condition at the casing for running NASA Rotor 37. The casing temperature is set to the inlet total temperature. Relative to the adiabatic simulations, the comparison to experimental efficiency is much improved for the 100% speed line. The efficiency difference between the isothermal and adiabatic solutions is about 1%, and matches the low-flow test condition. The profiles of total temperature with the isothermal boundary condition match the data near the casing. The adiabatic simulation has a total temperature overshoot that has been consistently part of any data comparison of CFD with this data set, and is typical of most compressor calculations. The efficiency profile has a similar improvement in matching the data because of its relationship to temperature. The real rig is not isothermal at the casing and may require more complex simulations such as a conjugate heat transfer approach to truly match the physics. However, the isothermal boundary condition is more accurate and more realistic than the adiabatic boundary condition.
A new turbomachinery design system, T-AXI, is described and demonstrated. It is intended primarily for use by educators and students, although it is sophisticated enough for actual designs. The codes, example cases and a user’s manual are available through the authors’ web sites. The design system can be used to design multistage compressors and turbines from a small number of physical design parameters. Students can understand the connection between these physical parameters such as Mach number and flow angles to the cross sectional area and angular momentum. There is also a clear connection between the angular momentum, work and blade loadings. Loss models are built-in and results are compared against tested geometries. The code also has a built-in blade geometry generator and the geometry can be output for running the MISES blade-to-blade solver on each section or visualizing the blades. A single stage compressor from the US Air Force Stage Matching Investigation rig, the 10 stage NASA/GE EEE high pressure compressor and the NASA/GE EEE 5 stage low pressure turbine have been used to validate T-AXI as a design tool.
The T-AXI turbomachinery design system, an axisymmetric methodology recently developed with an educational purpose, has shown great capabilities in the redesign of existing axial flow gas turbine components. Different turbomachines, single or multistage configurations, have been already reproduced with excellent overall performance results: examples are the NASA/GE E3 HP compressor and LP turbine. In this paper, the authors present a detailed analysis of the results of a “case-study” application of the code as a complementary tool to be used during a turbomachinery design course. The NASA/GE E3 HP compressor has been chosen as the test case. Starting from the data available in open literature the different steps of the redesign have been reported: from the flowpath generation through the thermodynamic properties distributions to the overall turbomachine performance analysis. Particular attention has been given to some critical aero design parameters. The links to some interesting and useful literature sources are reported. The free-vortex, the only vortex law included in the first version of the code has been used for a first EEE compressor redesign. Different design vortex methodologies have been implemented in the new release of the code and their effects on the angular momentum are reported. The corresponding geometries can also be interfaced to a mesh generator and then the turbomachinery configurations analyzed by a 3D Navier-Stokes solver. In this way the flow field can be carefully analyzed and the fluid-dynamic physics better understood. With the above software structure the student has the opportunity to test the effects of different design strategies on the turbomachinery performance and to understand the need of a hierarchy of tools that give complete information for the multistage turbomachinery design. Finally, in the last section of the paper, the authors present how a project such as T-AXI, developed from their research activity in turbomachinery, numerical methods and CFD, can be included in the education tool CompEdu.
A new turbomachinery design system, T-AXI, is described and demonstrated. It is intended primarily for use by educators and students, although it is sophisticated enough for actual designs. The codes, example cases, and user’s manual are available through the authors’ websites. The design system can be used to design multistage compressors and turbines from a small number of physical design parameters. Students can understand the connection between these physical parameters such as the Mach number and flow angles to the cross sectional area and angular momentum. There is also a clear connection between the angular momentum, work, and blade loadings. Loss models are built-in and results are compared against tested geometries. The code also has a built-in blade geometry generator, and the geometry can be the output for running the MISES blade-to-blade solver on each section or visualizing the blades. A single stage compressor from the U.S. Air Force Stage Matching Investigation rig, the 10 stage NASA/GE EEE high pressure compressor, and the NASA/GE EEE 5 stage low pressure turbine have been used to validate T-AXI as a design tool.
CFD simulations have been set-up with an isothermal boundary condition at the casing for running the NASA Rotor 37 axial compressor. The casing temperature was set to the inlet total temperature. The comparison to data was much improved for the efficiency for the 100% speed line relative to the adiabatic simulations. The efficiency difference between the isothermal and adiabatic solutions is about 1%, with the isothermal calculation matching the low flow test condition. The profiles of total temperature with the isothermal boundary condition matched the data near the casing without any overshoot, typical of most compressor calculations. Also the efficiency profile had a similar improvement in matching the data because of its relationship to temperature. A similar comparison between isothermal and adiabatic cases has been carried out for the same geometry with double the design clearance. The working range based on the steady CFD calculations is about half that of the design clearance case which is felt to be realistic. Moreover a detailed analysis based on conservation of Rothalpy has been made and applied to the rotor. Mass averaged Rothalpy is not conserved due to a frictional power term associated with the stationary case as well as heat transfer. The effects of these terms show the extent of the heat transfer is between 10–20% of span away from the casing. The heat transfer effect calculated with the isothermal boundary condition simulation is thought to be real, and accounting for it matches data better than using an adiabatic assumption. However, the real rig would probably not be isothermal at the casing and may require more complex simulations such as a conjugate heat transfer approach.
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