Today’s simulation and analysis (S&A) tools allow engineers to study and verify system/machine properties and visualize the aerodynamic, thermodynamic, structural, and other physical properties without having to build a physical prototype. We can perform cooling secondary flow systems analysis in a gas turbine; a detailed performance study for a supercritical CO2 turbine/compressor; predict cavitation for industry a water pump/rocket turbopump; and so many more. Products and machines are becoming more and more complex. Unfortunately, engineers only run a handful of designs through the S&A process, due to the cost associated with limited computer resources and the time required to run simulations and to create complex 3D models of designs. Furthermore, verification and certification of system designs are often done using actual hardware—a costly and time-consuming endeavor. Considering these aspects, 1D and 3D simulations are significantly important. However, engineers need to determine the trade-off between 1D and 3D simulation.
Imagine what’s required to generate one 3D design for a gas turbine secondary cooling flow system, and multiply it by 1,000 design alternatives. Even if we were to only use conceptual CAD models, this project would require extraordinary computing power and data storage—not to mention simulation and design expertise.
And so, even with the movement to bring more cloud-based S&A tools to market, resources required for 3D modeling will still result in very few designs being extensively explored, thanks to their complexity. Detailed low-dimensional models of system behavior can provide valuable insights into system performance and function thus guiding the design process. Read More
Supercritical CO2 (sCO2) power cycles offer higher efficiency for power generation than conventional steam Rankine cycles and gas Brayton cycles over a wide range of applications, including waste heat recovery, concentrated solar power, nuclear, and fossil energy. sCO2 cycles operate at high pressures throughout the cycle, resulting in a working fluid with a higher density, which will lead to smaller equipment sizes, smaller carbon footprint, and therefore lower cost. However, the combinations of pressure, temperature, and density in sCO2 power cycles are outside the experience of many designers. Challenges in designing sCO2 cycles include turbomachinery aerodynamic and structural design, bearings, seals, thermal management and rotordynamics. According to the report from Sandia National Lab, compressors operating near critical point and turbines have received only TRL (technical readiness level) 4 and 5 out of 9. This blog discusses the impact on turbomachinery design.
Radial or Axial
The selection of radial or axial for turbomachinery is typically performed based on the operating conditions (adiabatic head H and inlet volumetric flow Q). Non-dimensional turbomachinery parameters of specific speed Ns and specific diameter Ds can be selected from NsDs charts to estimate size, speed, and type of turbomachinery. Turbomachinery types for a sCO2 recompression cycle with scales ranging from 100 kW to over 300 MW have been studied and concluded that systems below 10 MW will likely feature only radial turbines and compressors with a single-stage or low stage counts. Such recompression cycle can be simulated in AxCYCLE™ tool which is shown in Figure 1. As size increases, the most efficient configuration for the turbine and recompressor transitions from radial to axial at approximately 30 MW and 100 MW, respectively. Suitable types of turbomachinery and its components for different power range can be reviewed in Figure 2. A radial configuration for the main compressor was expected at all scales due to its lower volume flow and wider range to facilitate variation in gas properties due to operation near the critical point.