Effect of Fan on Inlet Distortion: Mixed-fidelity Approach

Inlet distortion is typically encountered during off-design conditions on civil aircraft and in S-ducts in military aircraft. It is known to cause severe deterioration to the performance of a gas-turbine engine. As intakes become shorter, there is an increased interaction between the inlet distortion and the downstream fan. Previous studies in the literature use Reynolds-averaged Navier–Stokes or unsteady Reynolds-averaged Navier–Stokes to model this unsteady interaction, due to the substantial computational cost associated with high-fidelity methods such as large-eddy simulation/direct numerical simulation. On the other hand, it is well known that turbulence models have limitations in terms of predicting distorted flows. In this paper, a mixed-fidelity approach is proposed and employed to study the intake–fan interaction at an affordable computational cost. The results demonstrate that there are two mechanisms via which the fan affects the separated flow. First, the suction effect of the fan (effective up to almost half of the chord length upstream of the fan) alleviates the undesired distortion by “directly” changing the streamline curvature, intensifying the turbulence transport and closing the recirculation bubble much earlier. Second, the enhanced turbulence in the vicinity of the fan feeds back into the initial growth of the shear layer by means of the recirculating flow. This “indirect” feedback is found to increase turbulence production during the initial stages of formation of the shear layer. Both the direct and indirect effects of the fan significantly suppress the inlet distortion.The authors acknowledge the computing time on the UK national high-performance computing service ARCHER provided via the UK Turbulence Consortium in the framework of the EPSRC grant EP/L000261/1. This work is funded by a studentship from the Chinese Scholarship Council. The code for this project is provided by the Rolls-Royce plc

Dual Clustering Co-teaching with Consistent Sample Mining for Unsupervised Person Re-Identification

In unsupervised person Re-ID, peer-teaching strategy leveraging two networks to facilitate training has been proven to be an effective method to deal with the pseudo label noise. However, training two networks with a set of noisy pseudo labels reduces the complementarity of the two networks and results in label noise accumulation. To handle this issue, this paper proposes a novel Dual Clustering Co-teaching (DCCT) approach. DCCT mainly exploits the features extracted by two networks to generate two sets of pseudo labels separately by clustering with different parameters. Each network is trained with the pseudo labels generated by its peer network, which can increase the complementarity of the two networks to reduce the impact of noises. Furthermore, we propose dual clustering with dynamic parameters (DCDP) to make the network adaptive and robust to dynamically changing clustering parameters. Moreover, Consistent Sample Mining (CSM) is proposed to find the samples with unchanged pseudo labels during training for potential noisy sample removal. Extensive experiments demonstrate the effectiveness of the proposed method, which outperforms the state-of-the-art unsupervised person Re-ID methods by a considerable margin and surpasses most methods utilizing camera information

Towards Exascale Computation for Turbomachinery Flows

A state-of-the-art large eddy simulation code has been developed to solve compressible flows in turbomachinery. The code has been engineered with a high degree of scalability, enabling it to effectively leverage the many-core architecture of the new Sunway system. A consistent performance of 115.8 DP-PFLOPs has been achieved on a high-pressure turbine cascade consisting of over 1.69 billion mesh elements and 865 billion Degree of Freedoms (DOFs). By leveraging a high-order unstructured solver and its portability to large heterogeneous parallel systems, we have progressed towards solving the grand challenge problem outlined by NASA, which involves a time-dependent simulation of a complete engine, incorporating all the aerodynamic and heat transfer components.Comment: SC23, November, 2023, Denver, CO., US

Review of Advanced Effusive Cooling for Gas Turbine Blades

Turbine inlet temperature has continuously increased to improve gas turbine performance during the past few decades. Although internal convection cooling and traditional film cooling have contributed significantly to the current achievement, advanced cooling schemes are needed to minimize the coolant consumption and maximize the cooling efficiency for future gas turbines. This paper conducts a comprehensive review of advanced effusive cooling schemes for gas turbine blades. First, the background and the history of turbine blade cooling are introduced. Then, the metrics of effusive cooling efficiency are defined. Next, effusion cooling, impingement/effusion cooling, and transpiration cooling are reviewed. The flow and heat transfer mechanisms of the cooling schemes are emphasized, and the design trends of the cooling schemes are revealed. Finally, the conclusions and future research perspectives are summarized

Multi-fidelity simulation for a transonic compressor with inflow distortions

International audienceThe low and high fidelity methods are used to study a transonic fan case. This transonic fan case features a distortion generator upstream of the rotor. The low fidelity methods (immersed boundary method and immersed boundary method with smeared geometry) show promising results against hi-fi simulation (unsteady RANS) and experiments. The flow in the tip region, especially the interaction between the distorted inflow and tip leakage flow, are investigated in detail. It is found that the tip leakage flow is the dominant flow structure near the casing. It is strong enough to sustain even at the exit of the stator. Apart from analysing the tip leakage flow structures, the stalling mechanism is also explored. As mass flow decreases, more rotor blades are contaminated by the distorted flow. A rotating cell starts to develop shortly a er all the rotor blade passages are contaminated. The rotating cell is found to be swept in circumferential direction at the 65% speed of the rotor

Investigation of Unsteady Flow Interactions in a Transonic High Pressure Turbine Using Nonlinear Harmonic Method

The performance of a transonic high pressure turbine is mainly influenced by the unsteady interactions associated with the passing blades. In this paper, the unsteady flow interactions in a transonic turbine have been numerically investigated using the nonlinear harmonic (NLH) method in comparison with the steady and unsteady Reynolds-averaged Navier–Stokes (RANS). The comparison shows that the NLH method using three harmonics could capture the main unsteady flow interactions efficiently with about seven times smaller computational cost than the unsteady RANS, resulting in a more accurate time-averaged flow than for steady RANS. However, the continuity of the flow variables across the rotor-stator interface has shown some discrepancies compared with the unsteady RANS, which can be further satisfied by increasing the numbers of harmonics. The unsteady interactions are analyzed in detail; the results show that the wake and trailing edge shock from the upstream stator are the major sources of unsteadiness in the downstream rotor passage. The stator trailing edge shock impinges on the suction side of the passing rotor blades and generates pressure waves. These pressure waves are periodically reflected back to trigger the stator wake shedding. These waves are strong enough to travel through the rotor passage, and eventually affect the flow at the rotor’s trailing edge. The stator wakes are chopped by the downstream rotor, and travel through the rotor passage. This significantly enhances the unsteadiness of the flow near the rotor trailing edge. Lastly, the deterministic stresses and enthalpy distributions extracted from the NLH method have revealed that the effects of the unsteadiness are relatively weaker in the axial direction. Furthermore, the deterministic correlations analysis has shown that, some empirical deterministic correlations models based on the decay concept of compressors are not suitable for turbines