Due to the high Reynolds numbers together with the complex turbulent motions in turbomachinery, selecting a proper turbulence-modeling method is of vital significance in interpreting the real flow ...

Rotating instability (RI) can be regarded as a pre-stall signal because such phenomena are usually detected when a compressor operates at a near-stall point. Since RI is closely relevant to aerodynamic, acoustic, and structural issues, its mechanism has attracted industrial concerns and in-depth analysis. In this paper, a low-speed axial single compressor rotor row is selected as the baseline research object. A circumferential casing groove is mounted over the shroud. The solid casing and the casing treated configurations were simulated using the zonal large eddy simulation model, and the simulations present remarkable predictions in capturing the averaged and dynamic characteristics of the investigated compressor. By implementing a data-driven method called dynamic mode decomposition, the mode with the highest amplitude is proved to be correlated to the dominant RI frequency. The spatial and temporal property of the RI is visualized. The results show that the casing groove has limited influence on the averaged flow field but manipulates the dynamic features. The groove allows the RIs to shift from around 0.5 blade passing frequency to higher frequencies in the upstream region and effectively suppresses the unsteadiness in the zones under and downstream of the groove. The RIs are triggered by the flow interaction of the tip leakage flow at the front part of the blade. It can be depicted as pressure waves staggering with the rotor blade and propagating over the blade tip region at around half of the blade speed. With the existence of the casing groove, the dominant wavelength changes, and the fluctuation is damped under the groove, which finally modifies the properties of RIs.

When a compressor is throttled to the near stall point, rotating instability (RI) is often observed as significant increases of amplitude within a narrow frequency band which can be regarded as a pre-stall disturbance. In the current study, a single compressor rotor row with varying blade tip clearance (1.3%, 2.6% and 4.3% chord length) was numerically simulated using the zonal large eddy simulation model. The mesh with six blade passages was selected to capture the proper dynamic feature after being validated in comparison to the measured data, and the dynamic mode decomposition (DMD) approach was applied to the numerical temporal snapshots. In the experimental results, RIs are detected in the configurations with middle and large tip gaps (2.6% and 4.3% chord length), and the corresponding characterized frequencies are about 1/2 and 1/3 of the blade passing frequency, respectively. Simulations provide remarkable performance in capturing the measured flow features, and the DMD modes corresponding to the featured RI frequencies are successfully extracted and then visualized. The analysis of DMD results indicates that RI is essentially a presentation of the pressure wave propagating over the blade tip region. The tip leakage vortex stretches to the front part of the adjacent blade and consequently triggers the flow perturbations (waves). The wave influences the pressure distribution, which, in turn, determines the tip leakage flow and finally forms a loop.

Dense-phase CO2 pumps stand out as an effective method for transporting CO2 in Carbon Capture, Utilization, and Storage (CCUS). The pumps' characteristics are highly dependent on the operating temperature, which fluctuates with season and location. This paper studies the impact of inlet temperature on the performance of a multi-stage dense-phase CO2 pump. Numerical simulation, incorporating real gas properties, was performed to obtain flow details. Based on sparse samples, a physics-informed neural network (PINN) framework was introduced and trained to predict the overall performance. Compared to the random forest and traditional fully connected layer neural network, the PINN with an appropriate physical constraint demonstrates superior accuracy. The performance maps indicate that an increase in the inlet temperature leads to a decrease in overall pressure rise and shaft power. Additionally, the pump achieves a maximum polytropic efficiency exceeding 80% with higher inlet temperatures shifting the optimal efficiency point toward lower mass flow rates. A velocity triangle model, coupled with an entropy production theory, was proposed to elucidate the performance changes. It is found that the efficiency is governed by the flow fields. These findings provide insight into control and maintenance of dense-phase CO2 pumps in CCUS applications.