Turbo Machines Research Articles

Study on Control of Axial Thrust in Centrifugal Pump by Use of J-Groove

In order to control and balance the axial thrust of turbo machine, many types of devices such as balancing disk, balancing hole and sealing system are developed. However most of them are complicated and sometimes cause troubles such as the vibration by balancing disk. In this study, a very simple device of using shallow grooves mounted on a casing wall, known as “J-Groove”, is proposed and studied experimentally and theoretically. The experimental result shows that 70% of axial thrust in an industrial 4-stage centrifugal pump can be decreased at the best efficiency point. Moreover, a simple calculation method which can determine the optimum dimension of groove and its location is proposed.

원심펌프의 축추력 제어법에 관한 연구

In order to control and balance axial thrust of turbo machine, many types of balancing devices are used but most of them are complicated and sometimes cause troubles. In this study, a very simple device of using shallow grooves mounted on a casing wall, known as J-Groove, is proposed and studied experimentally and theoretically. The result shows that 70% of axial thrust in an industrial 4-stage centrifugal pump can be reduced at the best efficiency point. Moreover, the analytical method of interfered gap flow is established and a simple formula which can determine the optimum dimension of groove and its location is proposed.

Special Issue on the Magnetic and Electric Field Effects at the Micro- and Nano-Scale Systems and Flows in Material Processing

Special Issue on the Magnetic and Electric Field Effects at the Micro- and Nano-Scale Systems and Flows in Material Processing

Design and CFD analysis of centrifugal compressor for a microgasturbine

PurposeThis paper aims to show how a good compressor can be designed and modeled with CFD steady models and to explain reasons for discrepancies between experiment (1D design) and 3D CFD analysis.Design/methodology/approachA model with only one impeller channel was used to compare 1D design data, which were obtained from centrifugal compressor design code, written and developed by the authors. The often used model for CFD analysis of turbo machinery, known as “frozen‐rotor” model, only yields satisfying results for efficiency and pressure ratio, at and near the point of best efficiency. For this case, the static pressure shows a nearly uniform circumferential distribution at the inlet of the diffuser, which numerically leads to more homogeneous flow rates through the single vane channels, and thus to a more realistic time averaged flow distribution.FindingsThe numerical results with respect to performance data showed quite good agreement with experimental data at and near the operating point of best efficiency.Originality/valueThis paper offers a combined 1D and 3D numerical approach in turbo machinery design, especially in radial compressible turbo machines design.

高温ガス炉ガスタービンシステムの動力変換システム基本概念の評価

The design studies on High Temperature Gas Cooled Reactor with Gas Turbine (HTGR-GT) have been performed, which were mainly promoted by Japan Atomic Energy Agency (JAEA) and supported by fabricators in Japan. HTGR-GT plant feature is almost determined by selection of power conversion system concepts. Therefore, plant design philosophy is observed characteristically in selection of them. This paper describes the evaluation and analysis of the essential concepts of the HTGR-GT power conversion system through the investigations based on our experiences and engineering knowledge as a fabricator. As a result, the following concepts were evaluated that have advantages against other competitive one, such as the horizontal turbo machine rotor, the turbo machine in an individual vessel, the turbo machine with single shaft, the generator inside the power conversion vessel, and the power conversion system cycle with an intercooler. The results of the study can contribute as reference data when the concepts will be selected. Furthermore, we addressed reasonableness about the concept selection of the Gas Turbine High Temperature Reactor GTHTR300 power conversion system, which has been promoted by JAEA. As a conclusion, we recognized the GTHTR300 would be one of the most promising concepts for commercialization in near future.

Loss Analysis of Very Low Specific Speed Centrifugal Pump

In the range of very low specific speed ns, improvement of efficiency is the most important subject in order to apply turbo machine to such a low specific speed range. The purpose of the present study is focused on the performance improvement of pump in the range of ns?80 [m, m3/min, min-1], and CFD simulation is performed to determine the reason why efficiency is very low. The result shows that a rapid increase of leakage rate and disk friction rate with a decrease of ns is the main reason of low efficiency. Also, the result shows that if the leakage loss is reduced by use of Labyrinth seal at ns=25, the disk friction rapidly increases in spite of the leakage reduction and pump overall efficiency becomes only 5% higher.

Contact analysis of a flexible bladed-rotor

This paper presents a model of fully flexible bladed rotor developed in the rotating frame. An energetic method is used to obtain the matrix equations of the dynamic behaviour of the system. The gyroscopic effects as well as the spin softening effects and the centrifugal stiffening effects, taken into account through a pre-stressed potential, are included in the model. In the rotating frame, the eigenvalues' imaginary parts of the latter matrix equation give the Campbell diagram of the system and its stability can be analysed through its associated eigenvalues' real parts. The turbo machine casing is also modelled by an elastic ring in the rotating frame through an energetic method. Thus, in some rotational speed ranges the contact problem between the rotor and the stator can be treated as a static problem since both structures are stationary to each other. Prior to the study of the complete problem of contact between the flexible blades of the rotor and the flexible casing, a simple model of an elastic ring having only one mode shape, excited by rotating loads is developed in the rotating frame too, in order to underline divergence instabilities and mode couplings. Then, the complete problem of frictionless sliding contact between the blades and the casing, without rubbing, is studied. The stable balanced static contact configurations of the structure are found as function of the rotational speed of the rotor. Finally, the results are compared to these of the simple model of rotating spring-masses on an elastic ring, showing good adequacy. The present model of rotor appears thus particularly adapted to the study of blades-casing contacts and highlighted an unstable phenomenon near the stator critical speed even in case of frictionless sliding.

고분자 전해질 연료 전지용 공기공급계의 동특성 및 성능에 대한 연구

Turbo-blower as an air supply system is one of the most important BOP (Balance of Plant) systems for FCV(Fuel Cell Vehicle). For generating and blowing compressed air, the motor of air blower consumes maximum 25% of net power, and fuel cell demands a clean air. In this study, turbo-blower supported by air foil bearings is introduced as the air supply system used by 80kW proton exchange membrane fuel systems. The turbo-blower is a turbo machine which operates at high speed, so air foil bearings suit their purpose as bearing elements. Analysis for confirming the stability and endurance is conducted. The rotordynamic stability was predicted using the numerical analysis of air foil bearings and it is verified through experimental works. In spite of various transient dynamic situation, the turbo-blower had stable performances. After the performance test, results are presented. The normal power of driving motor has about 1.6 kW with the 30,000 rpm operating range and the flow rate of air has maximum 160 SCFM. The test results show that the aerodymic performance and stability of turbo-blower are satisfied to the primary goals.

Vibration Characteristics of a 75kW Turbo Machine With Air Foil Bearings

Air foil bearings are very attractive bearing systems for turbomachinery because they have several advantages over conventional bearings in terms of oil-free environment, low power loss, long life, and no maintenance. However, most of the developed machines using air foil bearings are limited to small and high-speed rotors of 60,000–120,000 rpm, since the increase in power of turbomachinery requires lower rotor speed and greater loading in bearings, which makes it difficult to use air foil bearings for large machines. In this paper, a 75 kW turboblower using air foil bearings is introduced, and the vibration characteristics of the machine have been investigated experimentally under a wide range of operating conditions, including compressor surge in the performance test. The machine is designed to be fully air lubricated and air cooled, and its operating speed is 20,000–26,000 rpm with maximum pressure ratio of 1.8. The results show that the air foil bearings offer adequate damping to ensure dynamically stable operation in the whole range.

Turbo machine tip clearance and vibration measurements using a fibre optic laser Doppler position sensor

This paper presents a novel fibre optic laser Doppler position sensor for single blade tip clearance and vibration measurements at turbo machines, which offers high temporal resolution and high position resolution simultaneously. The sensor principle is based on the generation of a measurement volume consisting of two superposed fan-like interference fringe systems with contrary fringe spacing gradients using wavelength division multiplexing. A flexible and robust measurement system with an all-passive fibre coupled measurement head has been realized employing diffractive and refractive optics. Measurements of tip clearance and rotor vibrations at a transonic centrifugal compressor performed during operation at up to 50 000 rpm (833 Hz) corresponding to 21.7 kHz blade frequency and 586 m s−1 blade tip velocity are presented. The results are in excellent agreement with those of capacitive probes. The mean uncertainty of the position measurement was around 20 µm and, thus, considerably better than for conventional tip clearance probes. Consequently, this sensor is capable of fulfilling the requirements for future active clearance control systems and has great potential for in situ and online tip clearance and vibration measurements at metallic and non-metallic turbine blades with high precision.

Non-contact blade vibration measurement analysis using a multi-degree-of-freedom model

The non-contact blade vibration measurement technique (tip timing) has been developed in the 1970s with focus on large steam turbine blades. Today, most of the turbo machine manufacturers are using tip timing for vibration amplitude or frequency evaluation of rotating blades. Different analysing methods have been developed. The most common method is a time domain analysis of a resonance passing using one- or two-blade sensors and a 1/rev sensor on the shaft. Normally, this analysing method is based on a single-degree-of-freedom resonator model. For mistuned blade rows, a single-degree-of-freedom model is not suitable. The possible errors of the single-degree-of-freedom model were repeatedly investigated. In this article, a multi-degree-of-freedom evaluation method is presented in detail. For the first time, a successful application on measurement data is reported.

Application of Computational Fluid Dynamics Analysis for Rotating Machinery—Part II: Labyrinth Seal Analysis

Labyrinth seals are used in various kinds of turbo machines to reduce internal leakage flow. The working fluid, or the gas passing through the rotor shaft labyrinth seals, often generates driving force components that may increase the unstable vibration of the rotor. It is important to know the accurate rotordynamic force components for predicting the instability of the rotor-bearing-seal system. The major goals of this research were to calculate the rotordynamic force of a labyrinth seals utilizing a commercial CFD program and to further compare those results to an existing bulk flow computer program currently used by major US machinery manufacturers. The labyrinth seals of a steam turbine and a compressor eye seal are taken as objects of analysis. For each case, a 3D model with eccentric rotor was solved to obtain the rotordynamic force components. The leakage flow and rotor dynamics force predicted by CFX TASCFlow are compared with the results of the existing bulk flow analysis program DYNLAB. The results show that the bulk flow program gives a pessimistic prediction of the destabilizing forces for the conditions under investigation. Further research work will be required to fully understand the complex leakage flows in turbo machinery.

Quantitative wind tunnel studies using pressure- and temperature sensitive paints

The pressure sensitive paint (PSP) intensity and lifetime system is an optical measurement technique to investigate absolute pressure fields on model surfaces for basic research in laboratories, industrial wind tunnels or high speed rotating turbo machines. Detailed qualitative and quantitative information and understanding of flow phenomena can be obtained in speed ranges from U$_{∞}$=20 m/s up to Ma=5.0. A number of projects of industrial interest has been investigated in different wind tunnels covering low speed, transonic, trisonic and cryogenic facilities. The influence of the main error sources for the components of the PSP system have been checked. Comparison of experimental pressure fields obtained by means of PSP and the results of numerical calculations have been carried out. Different wind tunnel models ranging from basic configurations such as a cropped delta wing to a complex half model of a large propeller-driven transport aircraft with all flaps, rudders and shrouds, and rotating or oscillating models as well as Reynolds number effects on models have been investigated.

Weldability of 17-4 PH stainless steel in centrifugal compressor impeller applications

Weldability of 17-4 PH stainless steel for centrifugal compressor impeller was considered. Welding tests were carried out on the precipitation-hardened steel of the 17-4 PH type. Possibilities of joining centrifugal compressor impeller parts as important elements of turbo machines were considered. Two means of welding (1 1 1) and (1 1 4), as well as following heat treatment have been considered. The best results: high tensile strength and high corrosion resistance were obtained for saturating for the wheels welded in temperature 1313 K/2 h followed by ageing in 893 K/2 h or only annealed for stress reliving in temperature 893 K/2 h after welding.

Proposal of the Atmospheric Pressure Turbine (APT) and High Temperature Fuel Cell Hybrid System

Solid oxide fuel cell (SOFC) has been extensively developed in many countries as an ultra-high efficient energy converter. Such high temperature fuel cell can be operated as a hybrid system of integrating of turbo machinery. A major decision is whether to place the cell stack in pressurized or unpressurized section. This paper discusses the exhaust energy recovery from fuel cells by use of turbo machines under unpressurized conditions, working with inverted Brayton cycle in which turbine expansion, cooling by heat exchanger and draft by compressor are made in an open cycle mode. It is denoted as “atmospheric pressure turbine (APT)”.

505 磁気軸受支持ターボ機械に作用する流体力の同定(磁気軸受・制御,OS-4 ロータダイナミクス)

505 磁気軸受支持ターボ機械に作用する流体力の同定(磁気軸受・制御,OS-4 ロータダイナミクス)

New practices for partial discharge detection and localization in large rotating machines

This paper presents a new technique for detection and localization of partial discharges (PD) in large rotating machines. In this technique, denoted InTech, a stator winding with (n) coils is equipped with (n + 1) inductive sensors; as a result, every stator coil is situated between two sensors. The measurement is then focused on the individual stator coils. In this way common difficulties facing partial discharge measurements in rotating machines such as attenuation and distortion of the signals in the stator winding, noise reduction, and the calibration accuracy are reduced considerably. The treatment of the sensor signals, using a special method, results in a measurement of PD in each respective stator coil. In addition, the stator coil from which the PD originates is identified. Results from field measurements on both hydro and turbo machines are presented and discussed.

FEM study and optimisation of a CMC outer liner

The possible employment of ceramic matrix composites (CMCs) in place of metals in the hot parts of the turbo machines is studied. The use of this class of materials should allow a relevant increase in the temperature of the gas with an increase in the overall efficiency. The CMC under study is a 12 layers laminate composed of alumina fibres embedded in a mullite matrix mounted with a crossply architecture. Thermal and stress analyses of a FE model of an outer liner is performed, and results are presented. These results are not completely satisfactory, and an optimisation process is applied to the component to identify that best material configuration, which results in six layers with an angleply architecture. An evident improvement is obtained, as the resulting stress level is significantly reduced.

A Unified Approach for Designing a Radial Flow Gas Turbine

Radial flow turbo machines have been used for a long time in a variety of applications such as turbochargers, cryogenics, auxiliary power units, and air conditioning of aircraft cabins. Hence numerous papers have been written on the design and performance of these machines. The only justification for yet another paper is that it would describe a unified approach for designing a single stage inward flow radial turbine comprising a rotor and the casing. The current turbine is designed to drive a direct-coupled permanent magnet high-speed alternator running at 60000 rpm and developing a maximum of 60 kW electrical power. The freedom of choice of the tip diameter and the tip width of the rotor that would be necessary for optimum isentropic efficiency of the turbine stage was restricted by the specified rotational speed and power output. Hence, an optimization procedure was developed to determine the principal dimension of the rotor. The mean relative velocity in the rotor passages in the direction of the flow would be accelerated but flow velocity on the blade surfaces experiences a significant space rate of deceleration. The rate of deceleration can be controlled by means of a proper choice of the axial length of the rotor. A prescribed mean stream velocity distribution procedure was used to spread the rate of deceleration of the mean flow velocity along the meridional length of the flow passages. The nozzle-less volute casing was designed to satisfy the mass flow rate, energy and angular momentum equations simultaneously. This paper describes the work undertaken to design both the rotor and the casing. The work was motivated by the growing interest in developing gas turbine based hybrid power plant for road vehicles. The authors believe that the paper would lead to a stimulating discussion.

Cross‐coupling and Unbalance Compensation of a Rigid Rotor

AbstractThe system under investigation is a rigid rotor supported by two active magnetic bearings. In this paper two coexisting sources of vibrations are considered. First, mass unbalance excitation as a synchronous periodic disturbance and second, destabilizing cross‐coupling forces as generated, for example, by fluid film mechanisms, annular pressure seals or labyrinths of a turbo machine. The basic AMB‐control is carried out by a simple PID controller while for the compensation of both excitation mechanisms two independent control algorithms are used. In order to compensate the destabilizing cross‐coupling forces a least square estimator estimates the unknown parameters of the cross‐coupling mechanism. The mass unbalance forces are compensated by a recursive gain scheduled algorithm. By combining these two algorithms a significant reduction of the vibration level is achieved.