Phase Distribution in the Tip Clearance of a Multiphase Pump at Multiple Operating Points and Its Effect on the Pressure Fluctuation Intensity

Tip clearance has a great effect on the flow and pressure fluctuation characteristics in a multiphase pump, especially at multiple operating points. The phase distribution and pressure fluctuation in tip clearance in a multiphase pump are revealed using the CFD (computational fluid dynamics) technology and high-speed photography methods. In this paper, the phase distribution, the gas-liquid two-phase velocity slip, and the pressure fluctuation intensity are comprehensively analyzed. Results show with the increase of the tip clearance, the multiphase pump pressurization performance is obviously deteriorated. In the meantime, the gas accumulation mainly occurs at the hub, the blade suction side (SS), and the tip clearance, and the maximum gas-liquid two-phase velocity difference is near the impeller streamwise of 0.4. In addition, the tip clearance improves the gas-liquid two-phase distribution in the pump, that is, the larger the tip clearance is, the more uniform the gas-liquid distribution becomes. Furthermore, the gas leads to the maximum pressure fluctuation intensity in the tip clearance which is closer to the tip leakage flow (TLF) outlet, and has a greater effect on the degree of flow separation in the tip clearance.

Efficiency Improvement Strategy for Multiple Operating Points in Doubly Fed Magnetic Geared Motor

The doubly fed magnetic geared motor, which has dual AC windings, can be operated with different frequencies in the inner and outer windings. However, the inner and outer windings have different numbers of pole pairs to meet the pole combination derived by the magnetic gearing effect, and hence undesirable space harmonic components of the magnetic flux are produced at the air gaps. These space harmonics affect the iron losses at each core, and the resultant iron loss and efficiency are varied by the frequencies of the inner and outer windings. Thus, in this paper, first, the effect of the space harmonic components of the air gap magnetic flux density in the inner stator, outer stator, and the modulating pieces is separately investigated. In addition, the iron loss characteristics of each ferromagnetic material are presented according to the frequency combinations in the inner and outer windings. Secondly, the iron loss maps and the efficiency maps according to the frequency conditions of the inner and outer windings are drawn, and the causes of the characteristic differences in each map are analyzed. Thirdly, the frequency control sequence and the roles of the inner and outer windings as the armature and field parts are changed, and the analysis of the iron loss map and efficiency map is repeated. Finally, the results in the inner-armature case and the outer-armature case are compared with each other, and the possibility of improving the overall operating efficiency over the multiple operating points by using the individual frequency control and frequency combination selection is proved.

Parametric Study for Adoption of Variable Cycle Engine Concept for Low Bypass Ratio Turbofan Engine

Turbojet and turbofan engine propulsion system are extensively used in aircraft. Turbojets have simple engine design and extensively used for supersonic flights. Turbofan engine has high mass flow rate and efficient for subsonic application. Variable Cycle Engines, unlike the traditional engines, can vary between high thrust mode for supersonic operations and high efficiency mode for subsonic operations hence are potentially attractive for supersonic transport and advanced tactical fighter aircraft. Variable Cycle Engine can be described as the one that operates with two or more cycles, could serve as a possible solution to reconciling the necessary performance at different operating conditions. The aim of the engine is to combine the best traits of turbojet (high specific thrust) and turbofan (low specific fuel consumption, low noise). Traditional engines have fixed mass flow but VCE can alter the mass flow and function as high bypass engine for the subsonic case and low bypass engine at the supersonic case. Different variable cycle engine design philosophies were studied and the engine architecture used in F120 was incorporated into the base design of a low bypass ratio Turbofan Engine. Cycle analysis of VCE was primarily done based on theoretical calculation and parametric study performed with the use of Gasturb software. Two Variable Area Bypass Injectors (VABI) were used to vary the mass flow through the core and the bypass stream. We aspire to achieve enhanced performance at subsonic and supersonic mission segments. Subsonic, supersonic and take off conditions were decided and the base engine was modified to have multiple operating points. The VCE combines two cycles (subsonic, supersonic) in same engine body and it is crucial for the engine components to deliver the required performance at both the design points. The engine design procedure consists of the matching of components like turbine, compressor, exhaust nozzle and the exhaust mixing area. Systematic study of turbine matching for such engine configuration with multiple operating points was carried out to understand the utility of variable geometry in a VCE. For turbine matching, the mass flow through turbine was held constant by adjusting the VABIs and this was repeated for different takeoff conditions to analyses the output in detail. The non dimensional mass flow through the turbine was fixed for both the design points and hence the turbine could be designed to provide high efficiency. The fuel consumption was found to have decreased compared to the baseline condition which in turn leads to low SFC and higher endurance.

Robust constrained model predictive control design for piecewise non-linear systems with multiple operating points

In this paper, a robust model predictive control (MPC) scheme is developed for non-linear systems. We propose a new modeling approach, entitled piecewise non-linear, for plants with multiple operating points and with unstructured uncertainties. The systems, in each subregion, are composed of an affine model perturbed by an additive non-linear term which is locally Lipschitz. Considering a non-linear term in the model changes the control problem from a convex program to a non-convex one, which is much more challenging to solve. A standard dual-mode control strategy is introduced by parameterizing the infinite horizon control moves into a number of free control moves followed by a single state feedback law. The designed controller is robust against model uncertainty and guarantees system stability under switching between subregions. Numerical examples on a highly non-linear chemical process and another non-linear system are used to evaluate the applicability of the proposed method. Simulation results show a better performance in terms of speed of convergence and feasibility compared with the conventional robust MPC designs.

Aerodynamic Optimization Process for Turbocharger Compressor Impellers

This paper presents the progression at BorgWarner Turbo Systems of the aerodynamic optimization process for radial turbocharger compressor impellers used in commercial vehicle applications. The design process was refined over several years, starting from relatively simple, single objective optimizations and moving to increasingly higher complexity with multiple operating points and objectives. CFD and numerical optimization techniques are used extensively with the aim of reducing costly gas stand testing with prototype hardware. Commercial software packages are used throughout for geometry definition, flow field evaluation, as well as an optimization scheduling providing genetic and gradient based algorithms. Design outcomes of the various developments were prototyped and tested at the BorgWarner Technical Center in Arden, NC. CFD predictions are compared with test data and discrepancies quantified. The resulting impeller designs show steady improvements with each design and methodology iteration, to the point that significant improvements in performance over conventional designs can be achieved consistently.