Quantitative analysis on influence of secondary flow for centrifugal impeller internal flow

The energy consumption and stability of centrifugal impellers can be effectively improved by using a lightweight material. Tip flow is the main factor affecting energy consumption and operational stability of centrifugal impellers. In this study, the mechanism underlying the influence of material weight on the flow in the tip region of a centrifugal impeller was explored. First, a numerical model of a bidirectional fluid-structure coupling was established and validated. Then, a comparative analysis was conducted on the vibration deformation of 17-4PH, titanium alloy, aluminum alloy, and epoxy carbon UD (CFP) impellers under extreme stall conditions. Finally, the changing trends of shock wave structure, leakage flow, and secondary flow in the tip region of these four kinds of impellers were compared and analyzed. The results show that tip clearance decreases gradually with decreasing impeller material density. By comparing with a stainless-steel impeller, the tip clearance of a CFP impeller decreased by 53% at most, and the total displacement decreased by nearly 100% (except in the case of resonance). The shock wave of the CFP impeller can be characterized by fast detachment, fast dissipation, and minimal countercurrent. The leakage flow of the CFP impeller was uniform, the leakage vortex moved forward slowly, the volume of the vortex was small, and the flow velocity on the blade surface was also small. With decreasing impeller density, the influence of the secondary flow on the main flow gradually weakened. These results lay a theoretical foundation for optimizing the structural and aerodynamic design of centrifugal impellers.

Influence of lightweight material on tip flow of a transonic centrifugal impeller based on bidirectional fluid-structure coupling

Li,

Zhang

2023

Aerothermal optimization of turbine cascade squealer tip with non-uniform squealer height

Cheng,

Shahid,

Zhou

et al. 2023

The squealer tip has significant influence on both the aerodynamic and heat transfer characteristics of the high-pressure turbine blade. However, due to the complexity of parameterization and meshing of the squealer and the complicated flow structure within the over-tip region, the existing squealer designs in the open literature have constant squealer heights. In this paper, the design space to the squealer height with non-uniform squealer height is extended and the new flow features it may bring are investigated. A parameterization system specifically designed for the non-uniform squealer height using five control parameters is implemented to automatically generate the geometry and hybrid meshes. Combining it with the multi-objective optimization system using genetic algorithms, a transonic turbine cascade squealer tip is optimized employing Reynolds-averaged Navier–Stokes k–ω shear stress transport model. The main objective of this study is to obtain a squealer configuration with the lowest total pressure loss coefficient and heat transfer coefficient. The optimum configuration with non-uniform squealer height achieves improvements in both the aerodynamic efficiency and the heat transfer performance, relative to the baseline conventional squealer tip geometry with the constant squealer height. Additionally, this work demonstrates that a flow structure in which the main flow forms a “blanket” below the leakage flow in the squealer is beneficial for aerothermal performance, especially reducing heat transfer losses, which provides valuable insight into the squealer tip design of advanced high-pressure turbines.

Asymmetric flow in a double-suction centrifugal fan induced by an inclined impeller

Chen,

He,

Yang

et al. 2024

The impeller and volute of a centrifugal fan are designed to be coaxially placed; however, the impeller might be inclined about the central axis of the volute due to installation fault, inducing asymmetric flow in the left and right halves of the fan. We performed a detailed numerical investigation on the non-uniform and asymmetric flow in a double-suction multi-blade centrifugal fan with a slightly inclined impeller using the unsteady Reynolds-averaged Navier–Stokes simulation approach. The impeller is assumed to rotate about each of the two minor axes perpendicular to the central axis to model the inclination. This work aims to quantify the influence of the impeller inclination on the aerodynamic performance of the centrifugal fan and to reveal the physics of transient flow in the two halves of the fan to demonstrate the impact of various inclination ways. Numerical results denote that a slight impeller inclination could stabilize the flow in the fan, while the flow is highly asymmetric as the inclination is enhanced, and the efficiency of the fan decreases due to the recirculation generated by the interaction of flow exiting from the impeller. An in-depth inspection shows sharply intensified pressure fluctuation at the collector, where the local clearance varies. The flow entering the collector and impeller substantially decreases in velocity, resulting in separated flow in part of the blade passages. The flow in the volute is also asymmetric since the impeller outlet is biased toward the volute wall.