The biomimetic turbine has an excellent flow drag reduction ability and wide incidence adaptability, so it has the potential to achieve high efficiency within a wide working range of high-performance variable cycle engines. A biomimetic cascade that can broaden the effective working incidence angles was designed based on a high-loading low-pressure turbine cascade, and its flow mechanism and aerodynamic performance were studied using experimental and numerical methods under the incidences angle (i) of 0° to 15° and Reynolds number of 1.0 × 10⁵. A series of counter rotating vortex pairs induced by the biomimetic cascade bring additional dissipation losses, but it accelerates the energy exchange between the boundary layer and mainstream, enhancing the dissipation of the pressure side leg of horseshoe vortex, and thus suppressing the flow separation and passage vortices. The undulating surface of biomimetic cascades can suppress the expansion of secondary flow in a spanwise direction in the end region, especially for large-scale separation under high incidence conditions. When i < 5°, the loss of biomimetic cascades is slightly higher than that of the original cascades, but the increase is only 0.5%; when i > 5°, the losses of biomimetic cascades are significantly reduced, with a maximum reduction of 70% at i = 15°.

Effects of electrical parameters on the flow characteristics of a plasma swirler are investigated. Through the accumulation of plasma induced acceleration, the azimuthal velocity is amplified when the fluid particles flow out of the plasma swirler. Numerical simulation is carried out to investigate the distribution of the azimuthal velocity and calculate the swirl number. The swirl number increases almost linearly with the increase of the electrode length until it reaches its maximum at the end of the electrodes. Fluid velocity distribution is quantitatively measured and analyzed using particle image velocimetry and laser Doppler anemometry. The higher the applied voltage is, the larger the flow divergence tends to be. With the increase of the applied voltage, the flow in the central region is modified, leading to the potential of flow control by adjusting the applied voltage.

In this study, a swirler combining the vane swirler and the plasma swirler is designed to control the flame lift-off height. The plasma swirler is located near the rim of the injector and the vane swirler is placed upstream of the plasma swirler. The vane swirler is employed to form a divergent flow to sustain the detached flame and the plasma swirler is adopted to control the flame lift-off height. The ionic wind clinging to the inner wall of the injector tube does not penetrate into the center, leaving the main stream flow in the central region largely undisturbed. Characteristics of the flow field are analyzed from the results of laser Doppler anemometry (LDA) measurement and mechanism of the flame lift-off control by the combined vane-plasma swirler is revealed. The flame lift-off locations calculated from the LDA measurement are consistent with those from direct observation. The dielectric barrier discharge (DBD) voltage influences the height of the flame lift-off with a linear relationship observed, which means the flame lift-off height can be controlled precisely by the DBD voltage without any mechanical movement or changing the mass flow rate. The combined vane-plasma swirler has the potential to improve the fuel flexibility, increase flame stability and attenuate the injector overheating. Highlights 1. A combined vane-plasma swirler is designed to control the flame lift-off height. 2. Flame lift-off height can be adjusted by changing the voltage of the dielectric barrier discharge. 3. A linear relationship between flame lift-off height and the dielectric barrier discharge voltage is observed. 4. Flame lift-off control by the combined vane-plasma swirler is mainly associated with the aerodynamic effect. 5. The swirler can improve fuel flexibility, increase flame stability and attenuate injector overheating.

Vortex breakdown, observed in swirling flows, is an interesting physical phenomenon relevant to a wide range of engineering applications, including aerodynamics and combustion. The concept of using a plasma swirler to control vortex breakdown was proposed and tested in this study. The effect of plasma actuation on controlling the onset and development of the vortex breakdown was captured by particle image velocimetry. Flowfield measurement results suggested that, by varying the strength of the plasma actuation, the location and size of the vortex breakdown region was controlled effectively. The plasma swirl injector offers a method for optimal control and efficient utilization of vortex breakdown. The method being proposed here may represent an attractive way of controlling vortex breakdown using a small amount of energy input, without a moving or intrusive part.

The interturbine transition duct (ITD), located between the high-pressure (HP) and low-pressure (LP) turbines of aeroengines, tends to be designed as an aggressive ITD integrated with wide-chord struts to meet the requirements of civil aeroengines for high bypass ratios and thrust–weight ratios. This paper presents a detailed unsteady numerical investigation of the effects of the HP rotor trailing-edge radius on the unsteady flow characteristics in the integrated aggressive interturbine transition duct (AITD), including the transport and dissipation of HP rotor wakes, the control mechanism of HP rotor wakes on flow separation and the influence of wake parameters. A sweeping rod, with a nondimensional diameter ranging from d/s = 0.056~0.143 (based on the pitch (s) of wide-chord struts at the midspan) and a reduced frequency ($f$) of 1.07, is used to simulate the HP rotor wake to decouple its influence from other secondary flows. Using the k-ω SST turbulence model and gamma–theta transition model, a structured grid with 6.3 million nodes can achieve similar global results. The wake in the lower part of the AITD channel dissipates rapidly because of the stretching between its own circumferential motion and the radial upward secondary flow, especially for a small d/s. Only the residual wake in the upper part can reach wide-chord struts in the case with large d/s. A sweeping rod with a large d/s can reduce the radial pressure gradient in the AITD, inhibit the internal secondary flow to a certain extent, reduce the dissipation rate of the wake, enhance its suppression effect on flow separation on a wide-chord strut, and decrease the flow loss. However, the wake can also enhance the passage vortex due to the increasing circumferential pressure gradient in the wide-chord strut channel, resulting in increasing blade profile loss. In the scope of this study, the aerodynamic gain of the wake is still not enough to compensate for its loss increment (including its own dissipation loss). Therefore, selecting a small trailing-edge radius of the HP rotor is conducive to improving the aerodynamic performance of the integrated AITD.