Periodic Reporting for period 2 - ROTRANS (Rotating Devices Performing Subsonic Supersonic Flow Transitions)
Reporting period: 2022-08-01 to 2023-07-31
1. Aerospace propulsion is intrinsically related to the passage of supersonic flows across a throat. It is, however, essential to address how we achieve the supersonic flow from an initial no-flow state. This process is called starting; as we transition from no flow into supersonic, a moving normal shock must be swallowed across the convergent passage. To ensure steady supersonic operation, one should avoid sonic conditions in the convergent section upstream of the throat. Self-starting is the process in which a passage may transition from subsonic to supersonic without any geometry change. It is essential to understand the underlying physics of this process to be able to reduce related losses significantly. For fast geometry generation and its assessment of flow starting a new design tool is required to evaluate this transient process efficiently.
2. Experimental validation of the transient models needs to be provided. Therefore an experimental facility needed to be designed to be able to assess transient flow phenomena in the transonic and supersonic regime. A shock generator was designed and built to be able to imitate the oblique shock occurring in a rotating detonation engine.
3. The evaluation of aerodynamic losses is an important challenge in the aerodynamic design of virtually any flow device. For the development of reduced loss models in supersonic flows, the loss creation in the boundary layer, the tip leakage vortex, or other secondary flow structures need to be analyzed. Also, it is required to analyze losses in a transient flow field to understand loss-creating mechanisms in a turbine exposed to the outflow of a rotating detonation engine. This way the performance of two different geometries can be compared and judged. Hence, the formulation of a physically consistent loss definition for aerodynamic losses derived from computational fluid dynamics CFD results was realized. Based on these loss analysis reduced models can be derived and implemented in a 1D Euler solver.
4. Rotating detonation engines and organic Rankine cycles would profit from efficient turbomachinery, which can perform a subsonic supersonic flow transition. To suit this need, a baseline geometry for the first turbomachinery stage has to prove the design concept. Following, a design optimization will explore the limits of this concept. For further efficiency gains and to allow for integration of the novel concept in existing engines a second stage needs to be designed to allow for the creation of the right outflow conditions.
Conclusions:
1. The underlying process of the normal shock movement during the starting process could be identified. This knowledge was used to design a reduced model for the rapid design of passages with improved startability.
2. An experimental facility that allows the testing of supersonic passages taking advantage of the hydraulic analogy was designed and built. The startability of several passages could be assessed confirming the numerically found trends. This way the in 1. designed reduced-order model could be validated. Furthermore, a shock generator was designed and built for the same facility. This shock generator allows us to imitate the occurring oblique shock in a rotating detonation combustor.
3. Aerodynamic and Aerothermal losses were defined based on the entropy transport equation. This allows the analysis of irreversible flow losses locally and at each time instance based on CFD results. This way complex CFD results with transient boundary conditions as the ones used in simulations of rotating detonation combustors can be assessed and the efficiency of turbines can be computed. A method to calculate the efficiency in an experimental setting was also proposed.
4. A new turbine technology was designed and optimized to take advantage of the pressure gain in a rotating detonation combustor. The technology was numerically assessed under transient conditions and showed dominant efficiency compared to known designs for this application.
2. Experimental validation of the transient models needs to be provided. Therefore an experimental facility needed to be designed to be able to assess transient flow phenomena in the transonic and supersonic regime. A shock generator was designed and built to be able to imitate the oblique shock occurring in a rotating detonation engine.
3. The evaluation of aerodynamic losses is an important challenge in the aerodynamic design of virtually any flow device. For the development of reduced loss models in supersonic flows, the loss creation in the boundary layer, the tip leakage vortex, or other secondary flow structures need to be analyzed. Also, it is required to analyze losses in a transient flow field to understand loss-creating mechanisms in a turbine exposed to the outflow of a rotating detonation engine. This way the performance of two different geometries can be compared and judged. Hence, the formulation of a physically consistent loss definition for aerodynamic losses derived from computational fluid dynamics CFD results was realized. Based on these loss analysis reduced models can be derived and implemented in a 1D Euler solver.
4. Rotating detonation engines and organic Rankine cycles would profit from efficient turbomachinery, which can perform a subsonic supersonic flow transition. To suit this need, a baseline geometry for the first turbomachinery stage has to prove the design concept. Following, a design optimization will explore the limits of this concept. For further efficiency gains and to allow for integration of the novel concept in existing engines a second stage needs to be designed to allow for the creation of the right outflow conditions.
Conclusions:
1. The underlying process of the normal shock movement during the starting process could be identified. This knowledge was used to design a reduced model for the rapid design of passages with improved startability.
2. An experimental facility that allows the testing of supersonic passages taking advantage of the hydraulic analogy was designed and built. The startability of several passages could be assessed confirming the numerically found trends. This way the in 1. designed reduced-order model could be validated. Furthermore, a shock generator was designed and built for the same facility. This shock generator allows us to imitate the occurring oblique shock in a rotating detonation combustor.
3. Aerodynamic and Aerothermal losses were defined based on the entropy transport equation. This allows the analysis of irreversible flow losses locally and at each time instance based on CFD results. This way complex CFD results with transient boundary conditions as the ones used in simulations of rotating detonation combustors can be assessed and the efficiency of turbines can be computed. A method to calculate the efficiency in an experimental setting was also proposed.
4. A new turbine technology was designed and optimized to take advantage of the pressure gain in a rotating detonation combustor. The technology was numerically assessed under transient conditions and showed dominant efficiency compared to known designs for this application.
1. In the performed work of this project the starting mechanism was analyzed on a fundamental level. After identifying the underlying physics of the starting problem, a fast model could be developed to optimize a geometry towards dominant startability. This model can generate a geometry with optimized starting capability within only 20 seconds.
2. An experimental facility was designed and built so that the starting capability of designed geometries can be assessed. A shock generator was designed and built to be able to analyze the impact of the oblique shock found in a rotating detonation engine on the turbine.
3. Results of reduced-order models could be validated by means of experimental data. The optimized geometry demonstrated improved startability in comparison to two slightly different geometries.
4. To analyze loss phenomena in discrete volumes in CFD results a method was derived to calculate the aerodynamic losses in the rotational frame and stationary frame of reference. This method was used to analyze the loss generation in the boundary layer, the tip leakage vortex, and other secondary flow phenomena both for a traditional transonic turbine and for a supersonic mixed flow turbine.
5. A novel type of turbomachine to harvest energy from a pressure gain combustor was developed and optimized.
6. A tool to generate geometries for transonic turbines, which perform a subsonic to supersonic flow transition was developed.
2. An experimental facility was designed and built so that the starting capability of designed geometries can be assessed. A shock generator was designed and built to be able to analyze the impact of the oblique shock found in a rotating detonation engine on the turbine.
3. Results of reduced-order models could be validated by means of experimental data. The optimized geometry demonstrated improved startability in comparison to two slightly different geometries.
4. To analyze loss phenomena in discrete volumes in CFD results a method was derived to calculate the aerodynamic losses in the rotational frame and stationary frame of reference. This method was used to analyze the loss generation in the boundary layer, the tip leakage vortex, and other secondary flow phenomena both for a traditional transonic turbine and for a supersonic mixed flow turbine.
5. A novel type of turbomachine to harvest energy from a pressure gain combustor was developed and optimized.
6. A tool to generate geometries for transonic turbines, which perform a subsonic to supersonic flow transition was developed.
The understanding of the fundamental mechanism that causes passage starting may have wide applicability in the aerospace industry. It may improve the performance of supersonic intakes as well as internal supersonic passages. Higher contraction ratios may be exploited with the novel design approach.
An experimental facility was shown to represent the starting process in a cost-effective way. This may support the rapid development more efficienct supersonic passages.
A method to evaluate aerodynamic and aerothermal power generation potential and flow losses in each volume element at each time instance will allow the assessment of any type of flow.
A newly designed type of turbomachinery to harness the power of rotating detonation combustors with high efficiency and beeing able to be integrated in traditional turbine engines
An experimental facility was shown to represent the starting process in a cost-effective way. This may support the rapid development more efficienct supersonic passages.
A method to evaluate aerodynamic and aerothermal power generation potential and flow losses in each volume element at each time instance will allow the assessment of any type of flow.
A newly designed type of turbomachinery to harness the power of rotating detonation combustors with high efficiency and beeing able to be integrated in traditional turbine engines