Janusz Piechna

A NOVEL DESIGN OF COMPOSITE WATER TURBINE USING CFD

This paper presents computational investigation of a novel design of composite material axial water turbine using Computational Fluid Dynamics (CFD). Based on three-dimensional numerical flow analysis, the flow characteristics through the water turbine with nozzle, wheel and diffuser are predicted. The extract power and torque of a composite water turbine at different rotating speeds were calculated and analyzed for a specific flow speed. The simulation results show that using nozzle and diffuser can increase the pressure drop across the turbine and extract more power from available water energy. These results provide a fundamental understanding of the composite water turbine, and this design and analysis method is used in the design process.

Feasibility study of the wave disk micro-engine operation

The development of micro turbine engines has been strongly intensified in recent years. Since turbo-component efficiency has become very low due to the downsizing effect, the micro wave rotor is expected to be applied for the improvement of the performance of ultra-micro gas turbines, increasing the cycle pressure ratio. But wave rotors can also be used in another configuration. Here replacement of steady flow engine components by unsteady flow devices is proposed and analyzed. Applying a combustion chamber only and using oblique blades to form the rotor cells, net power can be taken from the rotor. In that way the use of an inefficient, micro-scale turbo unit can be omitted. Conventional construction of unsteady devices in the form of a wave rotor cannot be realized in MEMS technology. The new idea of a wave disk gives the possibility of an easy implementation of a wave engine in MEMS technology. In the proposed solution the wave disk plays the role of an active compression–decompression unit and torque generator. Appropriate port geometry with straight or oblique blades forming the disk channels generates torque. The engine disk rotates with a speed much lower than the conventional turbo unit and simplifies the bearing problem. Also the construction of an electric generator could be simpler. This paper presents the proposed flow schemes, thermodynamic cycle, exemplary engine construction and some preliminary results of simulation of the MEMS wave engine utilizing the wave disk geometry.

NUMERICAL SIMULATION OF UNSTEADY- FLOW PROCESSES IN WAVE ROTORS

The wave rotor (pressure exchanger) is a device working based on a relatively simple idea of operation, but is challenging in its technical realization and difficult to simulate numerically. It has been common practice to create and use specialized codes for simulating the wave rotor operation. The current work presents an attempt of developing 2D and 3D models of radial and axial wave rotors using the commercial software package FLUENT. In this study geometrical models are used for the device casing and rotor cells. The application of carefully chosen initial and boundary conditions enabled the realization of relative motion of the rotor model. The vast information about the unsteady processes occurring during simulation are visualized. It occurs that such type of models are useful for the final test of devices, after the geometry was optimized by the use of specialized but much simpler 1D codes.

Numerical Solutions for Ultra-Micro Wave Rotors (UµWR)

‡Starting in 1995, with the MIT “Micro Gas Turbine” project, the mechanical engineering research world has explored more and more the idea of “Power MEMS” 1 . Microfabricated turbomachinery like turbines, compressors, pumps, but also electric generators, heat exchangers, internal combustion engines and rocket engines have been on the focus list of researchers for the past 10 years. The reason is simple: the output power is proportional to the mass flow rate of working fluid through the engine, or the cross-sectional area and the mass or volume of the engine is proportional to the cube of the characteristic length, thus the power density (Power/Mass=L -1 ). This is the so-called “cube square law”. Although in theory everything is perfect, the following investigations showed that there are many engineering challenges at microscale and the solutions found in the past half of century for large scale mechanical devices do not necessarily apply to the new design space. This paper studies the possibilities of incorporating a wave rotor to an ultra-micro gas turbine. It discusses the advantages of wave rotor as topping units for gas turbines, especially at microscale and proposes some designs of ultra-micro wave rotors. The numerical simulations of these wave rotors are presented, results obtained using FLUENT, a Computational Fluid Dynamics (CFD) commercial code.

Stability analysis in wound composite material axial impeller

A stability analysis is developed to assess the stresses and dynamic characteristics of the wound composite material axial impeller under centrifugal force loading conditions. This procedure is based on finite element analysis (commercial software ABAQUS) results. A low-cost, light-weight, high-performance composite turbomachinery impeller with a uniquely designed blade patterns is evaluated. Understanding the stress–strain behaviour of fibre-reinforced composite laminates as it relates to ultimate failure and the ability to predict ultimate strength is critical in the design of safe and lightweight impellers. To determine failures, the maximum stress failure criterion is used. In order to avoid operating at resonance, which can make impellers suffer a significant reduction in the design life, the designer must calculate the natural frequency and modal shape of the impeller to analyse the dynamic characteristics. The results show that using composite Kevlar fibre/epoxy matrix enables the impeller to run at a rotating speed 2228 rad/s and withstand the stresses, no critical speed will be matched during start-up and shut-down, and that mass imbalances of the impeller shall not pose a critical problem.

Computational Fluid Dynamics Investigation of a Novel Multiblade Wind Turbine in a Duct

A novel manufacturing approach similar to filament winding is able to produce high-performance and lightweight composite wheels. The production can be rapid, inexpensive, and utilize commercially available winding machines. One potential application of the wheel is as a wind turbine. It is widely accepted that placing a duct around a wind turbine can enhance its performance, especially when a new designed turbine with unique advantages has a relatively low power coefficient, it is necessary to examine the benefits and economics of a turbine in a duct. In this study, a numerical analysis of a ducted multiblade composite wind turbine using computational fluid dynamics (CFD) is evaluated and compared with a bare wind turbine of the same turbine area. This investigation was performed using FLUENT in conjunction with the GAMBIT meshing tool. The extracted power is calculated and compared for these two modeling designs. Through the comparison of power coefficient variation with thrust coefficient, it was found that a ducted turbine can be 2–3 times that of the power extracted by a bare turbine. The results of the analysis provide an insight into the aerodynamic design and operation of a ducted wind turbine in order to shorten the design period and improve its technical performance.

Compensation of Pressure Peaks in PWK-Type Hydraulic Pumps

Hydraulic axial pumps equipped with cam-driven commutation unit (PWK pumps) proved their high efficiency up to 55 MPa and ability to work self-sucking, even at high speed. Displacement of PWK pump may easily be changed by moving its control cam. Full discharge from hydrostatic forces makes such control possible by direct action of a low-energy actuator like proportional electromagnet or stepping motor. That eliminates heavy and costly hydraulic servomechanism, necessary in other variable displacement machines. Such a control mechanism was positively evaluated in prototype tests in Department of Hydraulics and Pneumatics of Gdańsk University of Technology. The new commutation unit generates however harmful pressure peaks. The paper presents the compensation method for pressure peaks by use of the elastic compensation chamber. It shows also results of multidisciplinary FEA and CFD analysis necessary to properly design the compensation chamber.

Modeling and Validation of a Pressure-Wave Supercharger Using a Finite Difference Method

Modern pressure-wave supercharging devices offer many degrees of freedom in operation with an internal combustion engine. Both the independent set of wave rotor speed and the offset between air and gas casing can guarantee optimum efficiency even under problematic operating conditions. However, these systems require very accurate models that can reproduce the physical effects occurring in the charger. In this paper, a finite difference tool is presented where a set of Euler-type partial differential equations is numerically solved to simulate the 1-dimensional unsteady gas dynamics in the cell wheel, taking into account such phenomena as leakage, heat transfer, and friction. In order to show its general applicability, the model was validated with measurement results from two different PWS-boosted engines on a test rig.Copyright

Experimental Investigation of the Dynamics and Space Range of the Gliding Arc in Three-Electrode System

The gliding discharge visualization in mixed streams of argon and oxygen was recorded with the use of a high-speed camera in order to test a plasma reactor new gas supply system, which consisted of two nozzles of a special shape. The plasma reactor was equipped with three electrodes powered by a three-phase alternating current. The estimated maximal discharge diameter was 32 mm. The diameter of the gas stream, where the stoichiometric composition of reactants was reached, amounted to 8 mm, and it was smaller than the maximal discharge diameter. In these conditions, it may be expected that the efficiency of the chemical reaction should be the highest for given experimental conditions.

Numerical Analysis of the Wave Topping Unit for Small Turbojet

The paper is focused on the numerical analysis of a wave topping unit used in a small turbojet engine. The analysis focuses on a four-port reverse flow (RF) wave rotor. The special feature of the considered wave rotor is its very high rotational speed. The wave rotor is connected directly with the common shaft between compressor and turbine, thus, the effects of Coriolis accelerations become important. In this study, first a one-dimensional model is used to estimate geometry of the wave rotor and port timings. Then, multi-dimensional analysis models are employed to predict the different flow characteristics inside the wave rotor channels. Three-dimensional flow features that reduce machine performance and influence rotor blade and duct wall thermal loads are identified.Copyright