Volume 36, Issue 1 -

Based on rotor dynamics theory, a two-disk flexible rotor system representing an aero-engine with freely supported structure was established with commercial software ANSYS. The physical model of the two-disk rotor system was then integrated to the multidisciplinary design optimization software ISIGHT and the maximum vibration amplitudes experienced by the two disks when crossing the first critical speed were optimized using a multi-island genetic algorithm (MIGA). The optimization objective was to minimize the vibration amplitudes of the two disks when crossing the first critical speed. The position of disk 1 was selected as the optimization variable. The optimum position of disk 1 was obtained at the specified constraint that the variation of the first critical speed could not exceed the range of ±10 %. In order to validate the performance of the optimization design, the proof-of-transient experiments were conducted based on a high-speed flexible two-disk rotor system. Experimental results indicated that the maximum vibration amplitude of disk 1 when crossing the first critical speed declined by 60.9 % and the maximum vibration amplitude of disk 2 fell by 63.48 % after optimization. The optimization method found the optimum rotor positions of the flexible rotor system which resulted in minimum vibration amplitudes.

Aiming at resolving the problem of measuring probe blockage effect in the performance experiments of high loaded axial flow compressors, an experimental investigation of the probe support disturbance effect on the compressor cascade flow field was conducted on a transonic plane cascade test facility. The influence characteristics of the probe support tail structure on the cascade downstream flow field under different operation conditions were revealed through the detailed analysis of the test data. The results show that the aerodynamic coupling effect between the upstream probe support wake and the downstream cascade flow field is very intense. Some factors, i. e. inlet Mach number, probe support tail structure, circumferential installing position of probe, and axial distance from the probe support trailing edge to the downstream cascade, are found to have the most impact on the probe disturbance intensity. Under high speed inlet flow condition, changing probe support tail structure can’t inhibit probe support disturbance intensity effectively. Whereas under low speed inlet flow condition, compared with the cylindrical probe, the elliptic probe can inhibit probe support wake loss and reduce disturbance effects on the downstream cascade flow field.

The following paper presents dynamic leakage rate and coupled interaction for variable speed rotor-labyrinth (LABY) seal, with rotating speed from 18 to 30 krpm. Variable speed rotor vibration characteristics are incorporated into transient computational fluid dynamic (CFD) calculations as boundary conditions of seal flow field to show the real-time effect of rotordynamic in seal flow field. Leakage rate across a variable speed rotor-seal increases with rotor vibration, but this effect is prominent at lower speed than at higher speed. Leakage characteristic is determined by differences in rotor vibration amplitude rather than rotating speed. The results also reveal that aerodynamic forces of labyrinth seal flow field can improve rotor stability, and this interaction between rotor and seal decreases with the increase of rotating speed.

The clearance has an obvious influence on the rotordynamic characteristics of brush seals. In order to better know the influence of brush seal on the stability of the rotor bearing system, the rotordynamic coefficients of labyrinth brush seal under different clearance cases and operating conditions are numerically analyzed using CFD RANS solutions coupling with a non-Darcian porous medium model. The results show that at the same geometry parameter the radial force and tangential force will increase when the pressure ratio rises. And when the clearance increases, the direct stiffness decreases sharply at first and then rises slightly. The variation of cross-coupled stiffness is complex. Moreover, at the same operating condition the value of direct damping coefficients increases when clearance increases, which add a stable factor to the rotor.

One-dimensional model is an important way to evaluate the performance and flow characteristics of dual-mode scramjet combustor. Current work is based on a modified one-dimensional model assisted by measurements acquired on a direct-connected scramjet facility. CH* images and gas-sampling facility have been employed to quantify heat release for optimizing one-dimensional model. The results show that modified one-dimensional model gives a better evaluation of axis parameters distribution, especially for Mach number, which is the standard parameter to evaluate combustion mode. The ram/scram mode derived by the analytical results has been investigated. Intensive heat release is beneficial to obtain more stable pre-combustion shock and subsonic flow in the recirculation zone.

Internal waverider inlets (IWIs) are novel three-dimensional (3D) high-performance inward turning inlets. However, they possess poor self-starting capacity when applied in a fixed-geometry inlet for ramjets. Firstly, this paper presents an analysis of self-starting capacity for IWIs to demonstrate that IWIs face more difficult challenges when used as ramjet inlets than they do as scramjet inlets. Self-starting capacity must be taken into account when designing ramjet inlets. Secondly, the impact of a fluidic control method on a fixed-geometry IWI was studied by numerical simulation of fluid flow. The numerical results show that the fluidic control mechanism improved the self-starting capacity of the IWI at low Mach numbers: the minimum Mach number of self-starting capacity was reduced from M3.8 to M3.2; furthermore, the compression ratio was increased from 29.9 with no fluidic control to 31.9. By analyzing two different groups of fluidic control positions, it was determined that bleeding before the separation bubble has no impact on the IWI self-starting capacity.

Soot formation and the effect of soot deposit on the performance and integrity on an aero gas turbine combustor has been studied. Defective atomizer or blockage of air passages creates a fuel rich mixture which promotes soot formation in combustor primary zone. The temperature field and soot concentration inside the liner has been analyzed at high equivalence ratio using computational model in CFX. The peak temperature in primary zone increases till equivalence ratio reaches ϕ=1.1. But at high equivalence ratio, i. e., ϕ≥1.2, the peak temperature in primary zone decreases and that in dilution zone increases. Soot concentration increases at liner front end as well as in dilution zone when equivalence ratio increases from 1.25 to 3.0. Erosion and distortion of atomizer flow passages cause higher spray cone angle which again increases the soot concentration. Soot deposit inside liner has detrimental effect on the life and performance of the combustor as well as of the aero engine.

Counter rotating turbine is an axial turbine with nozzle followed by a rotor and another rotor that rotates in the opposite direction of the first one. Absence of the second guide vane makes it more beneficial. Present work involves computationally studying the performance and flow pattern of CRT with different stagger angles ranging from 8 to 13° in case of rotor 2. Equivalent mass flow rates of 0.091 to 0.137 are considered. Turbine components nozzle, rotor 1 and rotor 2 are modeled for the cases of CRT with and without staggering. Total pressure, entropy and TKE distributions across the blade rows are used to describe the flow through CRT. Results show that the flow composition at the inlet of rotor 2 is improved for staggering cases. Due to this, the performance of rotor 2 and CRT increased with staggering. For the intermediate mass flow rate of 0.108, the efficiency of CRT stage is found to be increasing by 1.2, 2.1 and 1 % for the staggering cases. The beneficial aspect of staggering the rear rotor is thus confirmed that can provide long-term design solutions in terms of reducing weight, losses and improving the performance.

An industrial centrifugal blower with different volutes is investigated numerically for its aerodynamic performance and flow characteristics. Towards this, six different volutes are designed from a combination of three cross sectional shapes (parallel, rectangular and circular) and two area ratios (ratio 4.0 and ratio 5.0). A detailed analysis is carried out at design and off-design mass flow rates. Parallel wall volutes not only perform better but also improve stage performance among all cross sectional shapes explored. Parallel and rectangular volutes with ratio 4.0 exhibit higher stage performance, while, circular volute performs better with ratio 5.0. Flow inside the volutes is characterized in terms of circumferential pressure distribution at volute inlet, pressure recovery coefficients and velocity distribution across different cross sections. This detailed flow field investigation revealed the underlying physics behind the loss mechanism inside different volutes. The overall investigations suggest that the parallel wall volute is most compact and efficient one.

The measurement of the static pressure of the flow inside a supersonic ejector can be achieved by using a thin tube with a radially drilled hole to capture the flow pressure, and which is inserted along the ejector axis. This paper presents a numerical study by CFD permitting to predict the disturbances generated by the presence of the probe in the ejector. Also this study allows guiding the design of the probe, in particular of the capillary tube diameter for the least disturbed measurement. A probe prototype has been built and tested on an ejector test bench.

The self-supplying vortex generator jet (SVGJ) is introduced to the separation control of a high-speed compressor cascade with an inlet Mach number of 0.67. A parametric investigation concerning the jet location and the injection angle is conducted numerically. The effect mechanisms of SVGJ on the cascade performance are analyzed in detail. The potentials of SVGJ at off-design points are also discussed. The vortex generated by the jet utilizing the pressure difference between the pressure surface and suction surface could enhance the fluid exchange between the boundary layer and the mainstream, thus weakening the flow separation and reducing the flow loss effectively. With a hole of diameter 0.5 mm and a jet-to-inflow mass flow ratio less than 0.3‰, the maximum loss reductions are 5.2 % at the design point and 8.0 % at the off-design point, validating the high efficiency of SVGJ. In this work, the optimum performance is obtained by the SVGJ located at x j / B =40 %, h / H =15 % with a skew angle of β =60°.