Different methods to detect boundary layer transition are investigated within the scope of this paper. Laminar and turbulent boundary layers exhibit a significantly different behavior, not only regarding skin friction...Different methods to detect boundary layer transition are investigated within the scope of this paper. Laminar and turbulent boundary layers exhibit a significantly different behavior, not only regarding skin friction but also for heat-transfer which affects the blade cooling design. The present work presents a novel and non-intrusive measurement technique to detect the transition, based on acoustic concepts. The reliability of the technique was investigated by means of boundary layer measurements over a fiat plate in subsonic flow conditions. After a preliminary assessment with a conventional Preston tube, a row of microphones were installed along the plate to correlate transition pressure fluctuations. To provide a comprehensive representation of the experiment, dedicated measurements with a fast response aerodynamic pressure probe were performed to determine the turbulence intensity and the dissipation rate upstream of the flat plate. The experimental results were systematically compared with calculations performed with three different computational fluid dynamics solvers （ANSYS-Fluent, ANSYS-CFX, OpenFOAM） and using both the k-k1-ω and the γ-Reθ transition models. Results show a fair agreement between CFD （computational fluid dynamics） predictions and the acoustic technique, suggesting that this latter might represent an interesting alternative option for transition measurements.展开更多
At turbomachinery relevant flow conditions the boundary layers are often transitional with laminar-to-turbulent transition occurring. The characteristics of the main flow can depend highly on the state of the boundary...At turbomachinery relevant flow conditions the boundary layers are often transitional with laminar-to-turbulent transition occurring. The characteristics of the main flow can depend highly on the state of the boundary layer. Therefore it can be vitally important for the designer to understand the process of laminar-to-turbulent transition and to determine the position and length of the transitional region. In this paper the flow over a flat plate is experimentally studied in order to investigate and better understand transitional flow. Preston tube measurements as well as a thermographic camera system were performed for two different inlet velocities in order to determine the position of the transitional zone. The results of the experiment are compared to numerical flow solutions using a common transition model to determine its capability. The simulation has been performed with the two commercial codes CFX and Fluent by Ansys and an in-house code called LINARS. As a result of this study, a better understanding of the experimental and numerical methods for determining transition shall be given.展开更多
文摘Different methods to detect boundary layer transition are investigated within the scope of this paper. Laminar and turbulent boundary layers exhibit a significantly different behavior, not only regarding skin friction but also for heat-transfer which affects the blade cooling design. The present work presents a novel and non-intrusive measurement technique to detect the transition, based on acoustic concepts. The reliability of the technique was investigated by means of boundary layer measurements over a fiat plate in subsonic flow conditions. After a preliminary assessment with a conventional Preston tube, a row of microphones were installed along the plate to correlate transition pressure fluctuations. To provide a comprehensive representation of the experiment, dedicated measurements with a fast response aerodynamic pressure probe were performed to determine the turbulence intensity and the dissipation rate upstream of the flat plate. The experimental results were systematically compared with calculations performed with three different computational fluid dynamics solvers （ANSYS-Fluent, ANSYS-CFX, OpenFOAM） and using both the k-k1-ω and the γ-Reθ transition models. Results show a fair agreement between CFD （computational fluid dynamics） predictions and the acoustic technique, suggesting that this latter might represent an interesting alternative option for transition measurements.
文摘At turbomachinery relevant flow conditions the boundary layers are often transitional with laminar-to-turbulent transition occurring. The characteristics of the main flow can depend highly on the state of the boundary layer. Therefore it can be vitally important for the designer to understand the process of laminar-to-turbulent transition and to determine the position and length of the transitional region. In this paper the flow over a flat plate is experimentally studied in order to investigate and better understand transitional flow. Preston tube measurements as well as a thermographic camera system were performed for two different inlet velocities in order to determine the position of the transitional zone. The results of the experiment are compared to numerical flow solutions using a common transition model to determine its capability. The simulation has been performed with the two commercial codes CFX and Fluent by Ansys and an in-house code called LINARS. As a result of this study, a better understanding of the experimental and numerical methods for determining transition shall be given.
