Flow Structures in the Tip Region for a Transonic Compressor Rotor

Abstract

Numerical simulations are carried out to investigate flow structures in the tip region for an axial transonic rotor, with careful comparisons with the experimental results. The calculated performance curve and two-dimensional (2D) flow structures observed at casing, such as the shock wave, the expansion wave around the leading edge, and the tip leakage flow at peak efficiency and near-stall points, are all captured by simulation results, which agree with the experimental data well. An in-depth analysis of three-dimensional flow structures reveals three features: (1) there exists an interface between the incoming main flow and the tip leakage flow, (2) in this rotor the tip leakage flows along the blade chord can be divided into at least two parts according to the blade loading distribution, and (3) each part plays a different role on the stall inception mechanism in the leakage flow dominated region. A model of three-dimensional flow structures of tip leakage flow is thus proposed accordingly. In the second half of this paper, the unsteady features of the tip leakage flows, which emerge at the operating points close to stall, are presented and validated with experiment observations. The numerical results in the rotor relative reference frame are first converted to the casing absolute reference frame before compared with the measurements in experiments. It is found that the main frequency components of simulation at absolute reference frame match well with those measured in the experiments. The mechanism of the unsteadiness and its significance to stability enhancement design are then discussed based on the details of the flow field obtained through numerical simulations.

Unsteadiness of Tip Leakage Flow in the Detached-Eddy Simulation on a Transonic Rotor with Vortex Breakdown Phenomenon

“…The interaction results in extra complexity and less stability in the tip flow field, which is considered a hot spot. Strong self-induced unsteadiness was found in the TLV with a characteristic frequency near 60% BPF (blade passing frequency) [4,20,21] and the oscillation of passage shock was revealed as well [22]. Moreover, the casing boundary layer along with the blade surface boundary layer may participate in the interacting process [23], especially at near stall point where a shock-induced separation inside the boundary layer is likely to happen in most cases.…”

“…Driven by the pressure gradient inside the clearance of the rotor and casing, tip leakage is an unavoidable phenomenon in the field of turbomachinery, which scholars have studied for a long time in both compressible [1][2][3][4] and incompressible [5][6][7][8] fields. As for axial compressors, tip leakage flow plays an even more significant role due to its close relationship with loss and stall characteristics [9,10], which are highly valued in the design or analyzing processes.…”

Numerical Investigation for the Impact of Single Groove on the Stall Margin Improvement and the Unsteadiness of Tip Leakage Flow in a Counter-Rotating Axial Flow Compressor

“…It seems that there exists a critical chord interval of TLF and the CT is more effective when its groove acts on the critical portion of TLF. It has been found that the TLF along the chord can be divided into different parts and each part plays a different role on the stall inception mechanism in the tip region [9]. Generally, the TLF over the front portion governs the initial position of interface near the suction surface, while the rear portion of TLF interacts with the incoming flow near the pressure side of the neighboring blade and shifts the interface upstream, which may lead to the leading edge spillage of TLF.…”

“…The value of static pressure STD can be used to indicate the distribution of pressure oscillating strength [9]. The STD of static pressure is defined as below:…”

“…Up to now, much effort has been made to reveal the nature of TLF and researchers have made noteworthy progress on the potential relation between the stall inception and the unsteady phenomena in the tip region [3][4][5][6][7][8][9][10][11][12]. It has been found that the TLF could become unsteady at high loading operating conditions and the tip leakage vortex plays an important role in the stall inception process.…”