The flying squirrels of the tribe Pteromyini (Family Sciuridae) currently include 15 genera of which the genus Biswamoyopterus comprises two recognized species, B.biswasi Saha, 1981 and B.laoensis Sanamxay et al., 2013. These two species were each described from only one specimen that are separated from each other by 1,250 kilometres in southern Asia, where they occur in northeast India and central Lao PDR respectively. In 2017 and 2018, two specimens of Biswamoyopterus were discovered from Mount Gaoligong, west Yunnan province, southwest China (between the type locality of the two recognized species). This study aimed to evaluate the taxonomic status of these two newly acquired specimens of Biswamoyopterus by comparing their morphology with the two described species of the genus. The results of this study showed that the specimens from Yunnan province (China) differed from both B.laoensis and B.biswasi in both pelage colour and craniology, and should be recognised as a distinct species, B.gaoligongensissp. nov., which is formally described here. This study contributes to the understanding of the flying squirrels of southern Asia and identifies an additional species that appears to be endemic to southwest China; however, more research is required to provide details of its ecology, distribution, and conservation status.

The aero-engine casing is a key component for carrying loads. With the purpose of improving the thrust-weight ratio of the aero-engine, the casing is required to be designed to be as thin as possible. Therefore, the vibration of aero-engine's rotor, support, and casing will be easily coupled causing the whole engine's vibration to be more serious. Considering the structural vibration propagation is essentially the vibration energy transmission, the structural intensity (SI) method is popular and widely used to investigate the transmission phenomena of vibration energy in vibrating structures. This method combines forces with velocities to quantify the vibrational energy flow (VEF) transmitted in the structures by its directions and magnitude. Therefore, the SI fields are quantified by the developed computation system which combines the finite element design language and the in-house code. And a model of dual-rotor–support–casing coupling system subjected to the unbalanced forces of the rotors is established in this paper. The scalar and vector diagrams of instantaneous SI fields are visualized to show the main vibration energy transmission paths among these three parts. Moreover, the relationship between the SI and the mechanical energy is derived from the kinetic equation. According to this relationship, the phenomenon that the vibration energy and the strain energy are always converted to each other in the middle part of the rotor shaft with the first-order bending mode is discussed, which reveals the cause of the first-order bending mode of the rotor from a microscopic point of view.

A multistage vaneless counter-rotating turbine (MVCRT) eliminates vanes between rotors, which reduces the weight and size of the turbine and avoids viscous losses associated with vanes pronouncedly. An aircraft engine employing such a turbine would have greater thrust to weight ratio and smaller specific fuel consumption. This paper presents the aerodynamic design philosophy and performance analysis of the MVCRTs for gas turbine engines by a case study. The case is about a 1/2*4 turbine, which consists of a rotating frame and four rotors without any vanes between them. The first rotor and the third rotor are connected by a shaft to drive a compressor with a pressure ratio of 11.8, and the second rotor and the fourth rotor are connected by the rotating frame to deliver a total shaft power of around 2 MW. The stage loading of each rotor and flow axial acceleration of each duct are controlled to provide sufficient inlet swirls for their subsequent rotors. The stage work coefficients of each rotor are 0.95, 2.9, 1.4, and 1.0, respectively. Nonuniform radial circulation distributions are also used to maximize the turbine power output. Centrifugal forces in the outer rotor of the turbine are captured by carrying out a finite element analysis (FEA) to validate the aerodynamic design results. Three-dimensional viscous numerical results show that an adiabatic total-to-total efficiency of 91.47% with a pressure ratio of 9.8 at design condition is obtained and achieves the initial design objective very well. Entropy creation associated with the tip leakage and secondary flow is also illustrated for understanding the origins and effects of losses in the turbine. Pressure ratios and efficiency at the speed combinations of the 80% to 100% inner and outer rotor design speeds are discussed to reveal the turbine characteristics at off-design conditions.

A zero inlet swirl turbine rotor (ZISTR) works with axial inlet gas flow directly exhausted from a combustion chamber without any upstream vanes. The suction side trailing edge shock of the ZISTR generates a significant amount of aerodynamic loss. A shock loss reduction method is presented for the ZISTR. The principle of the method is to replace the single shock by double shocks. For minimizing the shock loss, the strength of the double shocks is set to be equal. This is based on a design criterion that multiple shocks should be with equal strength to achieve the minimum shock loss. This design criterion has been widely used for supersonic inlet design, but it is first extended to the transonic turbine design in the present article. A shock model, using aerodynamic relations of oblique shock, is put forward to quantitatively determine the shape of the concave suction-side profile. Numerical simulations indicate that the concave suction-side profile induces a new shock upstream of the suction-side trailing edge shock, and these two shocks are with nearly equal strength in the improved ZISTR. The shock loss of the improved ZISTR is obviously reduced. The concave tip profile would redistribute the blade load on the tip and increase the tip leakage flow loss. Hence, it is suggested that the concave profiles should be designed between 0% and 80% blade span, and the tip profile should keep unchanged. The improved ZISTR with an unchanged tip profile achieves an improvement of turbine efficiency by 0.8% at the design condition.

The effect of upstream wake vortex on the unsteady characteristics of downstream tip leakage flow (TLF) in a high-loading counter-rotating compressor, have been revealed. For the strength of the tip leakage vortex (TLV) is stronger than that of the upstream wake vortex and the TLF spills from the leading edge (LE) of the neighbor blade under near stall (NS) condition, the wake vortex can only transport bypass the interface, formed by the TLF and main flow, just below the tip. The TLV is separated into several parts by the wake vortex such that it weakened rapidly and the dominant frequency of the static pressure fluctuation near the trailing edge (TE) is about 1 relative blade passing frequency (RBPF) under the NS condition. When the extent of TLV breakdown is enough, the TLV is responsible for the dominant frequency near the LE. Therefore, there are two dominant frequencies (one is located near LE, the other is located near TE) in the tip region of the downstream supersonic rotor under NS condition. It’s harmful for the stable operation of compressors due to lower frequency resulting from TLV. At small tip clearance size, affected by the upstream wake vortex, when the static pressure fluctuation caused by the TLV at the LE of the downstream rotor just appeared, the momentum ratio increases. And it locates above the limit line (applied to judge the static pressure fluctuation caused by the self-excitation of the TLF), this means the wake vortex is beneficial to suppress the self-excitation of the TLF.

Active control of the inlet flow area in a centrifugal compressor is a method to improve compressor aerodynamic performance and stall margin. As a core part of the area control device, the variable geometry orifice is investigated and its two key design parameters are analyzed in detail, the setting angle of the orifice with respect to the shroud casing and the radial height of the orifice to the shroud casing from the orifice inner rim. This paper proposes a physics-based equation that describes the relationship of the two parameters with compressor mass flow rate and then validates the equation using numerical simulations. As far as the setting angle, the physics-based equation suggests not to be larger than 90°. The numerical results not only validate the physics-based equation but also show the most optimal angle of 78°. In terms of the orifice height, both the physics-based equation and the numerical simulations suggest an active height control of orifice in the compressor inlet duct.