Vane Setting Angle Research Articles

Experimental Study on Inducement and Development of Flow Instabilities in a Centrifugal Compressor with Different Diffuser Types

A centrifugal compressor is a typical compressed air energy storage device. In order to ensure the safety of the compressed energy storage process in the compressor, the internal unsteady flow phenomena need to be closely monitored, especially some serious ones like stall and surge. It is necessary to explore the mechanism of flow instabilities under different conditions. A centrifugal air compressor was tested with a vaneless diffuser and a variable vaned diffuser with five different vane setting angles, respectively. Various diffuser types resulted in various modes of flow instabilities prior to surge. The vaneless region between the impeller and the diffuser was focused on. Multiple high-speed sensors were arranged along the circumferential direction. The pressure signals at all these positions were being measured and collected in real time as the compressor was slowly throttled into surge. This paper emphasizes on the influence of matching between the impeller and the diffuser on the flow instability. The experimental results showed that the diffuser vane setting angle affected the stall characteristics. Due to the asymmetry of the volute, the circumferential pressure distribution was always severely distorted prior to surge. A high-pressure region appeared near the volute tongue, and a low-pressure region was formed away from the volute tongue. In the case of the vaned diffuser with non-design installation angle and the vaneless diffuser, the rotating stall signal was originated in the low-pressure region and propagated circumferentially. However, in the case of the vaned diffuser with the design installation angle, the circumferential high-pressure region became the most sensitive region for the generation of stall, and another form of instability occurred there. Both the inducement and development of these flow instabilities have been studied. The dynamic experimental research on the compressor matching different types of diffusers could be a good case supplement.

Experimental and Numerical Analysis of Different Unsteady Modes in a Centrifugal Compressor With Variable Vaned Diffuser

The flow instability always varies within different compressors; however, even in one compressor, there may be still multiple various unsteady modes. To study the triggering mechanism for these unsteady modes, a detailed experimental research on an industrial centrifugal compressor with variable vaned diffuser is performed from design point to surge. The multiposition dynamic pressure measurement is conducted during the whole valve-adjusting process. The characteristics of pressure fields under some specific operating conditions are focused on, especially the prestall, stall and surge conditions. According to the collected data, the features of different unsteady modes can be obtained, such as the surge pattern and the propagation direction of stall cells. In addition, when the diffuser vane setting angle (DVA) is adjusted, the core factors to trigger total instability will change. To better complement the experimental analysis, a multipassage numerical simulation is carried out. Based on the agreement of performance curves obtained by the two methods, the flow field characteristics in the prestall state shown in the simulation results are indeed a good complement to the dynamic experimental analysis. Meanwhile, with the help of dynamic mode decomposition (DMD) method, a few low-frequency unsteady structures are extracted from the transient numerical result over a long time, which correlate with the experimental result. Through detailed analysis, an insight into the different unsteady modes in a centrifugal compressor with variable vaned diffuser is obtained.

Experimental and numerical investigations of tip clearance flow and loss in a variable geometry turbine cascade

Variable geometry turbines are widely employed to improve the off-design performance of gas turbine engines; however, there is a performance penalty associated with the vane-end partial gap required for the movement of variable vanes. This paper is a continuation of the previous work and aims to understand the leakage flow and loss mechanisms under the influence of the pivoting axis. Experimental investigations with a variable geometry turbine linear cascade have been conducted for tip gap heights of 1.1% and 2.2% blade spans as well as setting angles of −6°, 0°, and 6°, so as to reveal the three-dimensional clearance flow characteristics associated with partial gaps. Besides, numerical predictions are also carried out to better understand the experimental results. Pressure measurements were performed on the tip endwall as well as on the vane surface, and three-dimensional clearance flow fields downstream of the variable cascade were measured with a five-hole probe. The results show that as the vane setting angle is changed from design to closed, the vane loading increases and tends to be more aft-loaded, thus increasing the tip leakage loss, and vice versa. There are strong interactions between the flow around the pivoting axis and the leakage flow in the vane tip rear part, which leads to a low-pressure region on the tip endwall. The leakage vortex core is made up of the leakage flow in the vane tip rear part at both two tip gap heights, and the leakage vortex core formation process is different from the one in the rotor blade. The present results can provide useful references for the vane-end clearance design of variable geometry turbines.

Experimental Study on the Effect of Diffuser Vane Setting Angle on Centrifugal Compressor Performance

The effect of the diffuser vane setting angle on the performance of a centrifugal compressor was experimentally investigated. Seven different vaned diffusers were tested with the same impeller. In order to evaluate the vaned diffusers under the same flow range and diffuser inlet conditions, all the diffusers were designed to have the same throat area, the same diffuser height. and the same vane inlet position. The first tests were performed by a compressor with a volute. In this case, the diffuser outlet conditions were varied along the circumferential directions due to the nonaxisymmetric geometry of the volute. In the second tests, four of the seven vaned diffusers were tested using a compressor with a collector. In this case, the diffuser outlet conditions were more uniform along the circumferential directions compared to the tests using the compressor with the volute. The effect of the vane setting angle on the stage characteristics and diffuser performance as well as the effect of the circumferential distortion caused by the volute on the stage characteristics are presented. The impact of the incidence loss on the vaned diffuser performance is discussed using 1D vaned diffuser performance modeling. Comparisons of the 1D predictions and the tests results show the incidence loss has a strong influence on vaned diffuser performance.

가변안내깃 설치각이 다단 축류압축기 성능에 미치는 영향

일반적으로 다단 축류압축기는 부분 부하 조건에서 충분한 운전영역을 확보하기 위해 가변안내깃을 이용한다. 본 연구에서의 해석대상인 다단 축류압축기는 입구에서의 안내깃과 함께 1단과 2단 정익을 가변안내깃으로 하여 운전영역을 확보한다. 따라서 본 연구에서는 정격회전수의 70%와 90% 회전수 조건에서의 가변안내깃의 설치각이 다단 축류압축기의 성능에 미치는 영향에 대해 조사하였다. 다단 축류압축기의 성능은 3차원 정상상태 및 비정상상태 수치해석을 이용하여 확보하였다. 각 해석기법을 통해 확보한 결과를 비교하였으며 내부유동장의 특성을 파악하였다. Generally the variable guide vane is used to secure the sufficient operating point in the off-design condition. In this study the inlet guide vane, 1st and 2nd stators in a multi-stage axial compressor are movable to obtain the operating range. So the effects of variable guide vane setting angle on the performance of 2.5 stage axial compressor were investigated at 70 % and 90 % conditions of nominal rotating speed in this paper. The steady-state and unsteady numerical analyses were conducted at each operating condition. The performance map, lost efficiency and flow fields were compared.

固定式 OWC 型波力発電用衝動タービンの効率に関する実験的研究

An oscillating water column (OWC) type wave energy converter is composed of a partly submerged wall, an air chamber, an air turbine and a generator and is considered to be safe even under the storm condition. Besides, an impulse turbine as the secondary conversion device in the OWC unit is expected to achieve the high efficiency. In the previous research, the authors investigated the effects of the air chamber length on the primary and secondary conversion efficiencies experimentally. Continuously, in this paper, the 2-D wave tank tests in regular waves for the performance evaluation of the fixed OWC type wave energy converter with the impulse turbine were conducted, and the effects of the impulse rotor inlet/outlet angle, the guide vane's number and the guide vane's setting angle are shown experimentally.

Low Field in the Vaned Diffuser of a Centrifugal Pump at Different Vane Setting Angles

Particle image velocimetry (2D-PIV) has been used for the investigation of the time and phase-averaged flow field inside the vaned diffuser of a centrifugal pump operating at the best efficiency point (BEP). Pump performances and the diffuser flow field were analyzed for three different vane setting angles. It was evidenced that flow coefficient at the best efficiency point decreases with the diffuser setting angle reduction. From 2D-PIV measurements in five different blade to blade planes, spanwise averaged flow angles and velocity distribution were computed. It was evidenced an influence of the diffuser setting angle on the spanwise distribution of the flow rate and of the absolute mass averaged flow angle at impeller discharge. An overturning at the diffuser discharge was also evidenced for the two highest setting angles. 2D-PIV flow fields are presented in three different pseudosecondary planes in order to enlighten the cross flows affecting the diffuser flow field.

Flow Through a Solar Chimney Power Plant Collector-to-Chimney Transition Section

A solar chimney power plant consists of a large greenhouse-type collector surrounding a tall chimney. The air, heated within the collector, passes through an inlet guide vane (IGV)cascade and then through a transition section to a turbine that powers a generator. The transition section contains the turbine inlet guide vanes that support the whole chimney and guides the flow entering the turbine. The primary objective of the study was to determine the loss coefficient and mean exit swirl angle of the flow passing through the collector-to-chimney transition section of a full-scale solar chimney power plant as dependent on IGV stagger angle and collector roof height. Very good agreement was found between experimental values measured in a scaled model and commercial CFD code predictions of flow angles, velocity components, and internal and wall static pressures. The agreement between measured and predicted total pressure loss coefficient was reasonable when considering how small it is. The CFD code served to extend the predictions to a proposed full-scale geometry. Semi-empirical equations were developed to predict the loss coefficient and turbine mean inlet flow angles of solar chimney power plants as dependent on collector deck height and inlet guide vane setting angle. The two empirical equations may be useful in solar chimney plant optimization studies.

Effect of the setting angle of a low-solidity vaned diffuser on the performance of a centrifugal compressor stage

The present investigation is undertaken to study the performance of an existing stage of an industrial centrifugal compressor with a vaneless diffuser and is aimed at improving the efficiency of the compressor stage through the use of a low-solidity (LSD) vaned diffuser. The experiments were conducted at a tip Mach number of 0.35. The LSD vane is formed from a standard aerofoil profile with marginal modification in the trailing edge region. The study was conducted at a solidity ratio of 0.81, which is considered as the optimum for the chosen stage. The overall stage performance for different diffuser vane setting angles was evaluated in terms of flow coefficient, head coefficient, polytropic efficiency and static pressure recovery coefficient. The performance parameters are normalized with respect to those of the vaneless diffuser at design flow. Improvement in performance as well as static pressure recovery was observed with LSD vanes as compared with a vaneless diffuser configuration. Variation in blade loading was studied from measurements of static pressure on the pressure and suction surfaces of LSD vanes at different vane setting angles. It was observed that the vane setting angle has a significant effect on stage performance and also on the blade loading.

Study on Vaned Diffuser Performance (Analysis of Effect of Vane Setting Angle on Vaned Diffuser Performance)

Study on Vaned Diffuser Performance (Analysis of Effect of Vane Setting Angle on Vaned Diffuser Performance)

Experimental and numerical investigation of the performance of a 240 kW centrifugal compressor with different diffusers

Eight low solidity vaned diffusers (LSVD1–LSVD8) were designed for a 240 kW centrifugal compressor. All eight LSVDs and for comprison purposes along with two standard and high performing vaneless diffusers and one conventional vaned diffuser were tested downstream of the same impeller. The objective was to understand the pressure recovery phenomena in each of the three types of diffusers, and the effect of design parameters on performance. Also, the results were compared with the results from numerical simulation. The design parameters include the solidity, turning angle, vane setting angle, and the number of vanes. The experimental investigation was performed at three different rotational speeds ( M u=0.69, 0.88, 1.02). The experimental results proved the superior merits of the LSVDs relative to the vaneless and vaned diffuser. The LSVDs fulfilled the high expectations, since they seemed to combine the advantages of the conventional diffusers by providing a good pressure recovery over a wide flow range.

Effect of circulation on critical submergence of an intake pipe

In this study, the effect of circulation on the critical submergence of an intake pipe is presented. Experiments were conducted on a vertically flowing downward intake pipe in a circulation imposed still-water reservoir. The circulation imposed on the flow causes an outward centrifugal force component in radial direction which increases the critical submergence considerably. For a given flow and geometry, the vane setting angle has a certain value which causes the same critical submergence as in the case of no-vanes (unsteady vortex in no-circulation imposed flow). As the vane setting angle gets larger than its certain value, the critical submergence becomes larger than that in the no-circulation imposed flow (no-vanes). The smaller the vane setting angle, the smaller is the critical submergence. The critical submergence attains its minimum value when the vane setting angle is zero (vanes are set radially). Flow visualization for an intake pipe in a still-water reservoir has indicated that a spherical volume of fluid bounded by a stream surface of a sphere (SSS) develops. This spherical volume, hence SSS, shrinks radially and rotates about its vertical axis. The air-entraining vortex occurs as the SSS collapses. The SSS is a useful concept for the physical explanation of occurrence of the air-entraining vortex.

Performance prediction of axial flow compressors using stage characteristics and simultaneous calculation of interstage parameters

A new method for predicting performance of multistage axial flow compressors is proposed that utilizes stage performance curves. The method differs from the conventional sequential stage-stacking method in that it employs simultaneous calculation of all interstage variables (temperature, pressure and flow velocity). A consistent functional formulation of governing equations enables this simultaneous calculation. The method is found to be effective, i.e. fast and stable, in obtaining solutions for compressor inlet and outlet boundary conditions encountered in gas turbine analyses. Another advantage of the method is that the effect of changing the angles of movable stator vanes on the compressor's operating behaviour can be simulated easily. Accordingly, the proposed method is very suitable for complicated gas turbine system analysis. This paper presents the methodology and performance estimation results for various multistage compressors employing both fixed and variable vane setting angles. The effect of interstage air bleeding on compressor performance is also demonstrated.

Effects of Parameters of Mixed Flow Multiblade Fan Impeller on Performances.

In the former report, advantages of using a small duct for an air conditioning system were mentioned, and it was presented that the mixed flow multiblade fan, which was developed newly by authors, was adequate to a small duct fan. In this paper, the effects of parameters of the mixed flow multiblade fan on the fan performances were investigated experimentally. At first, the effects of a conical angle of the impeller and a vane setting angle on the performances were investigated. Then, two types of guide vanes were examined, and it was made clear that the guide vanes which overhang the impeller gave remarkable effects on the fan pressure and efficiency. At last, the experimental results regarding to effects of the inlet and outlet vane angles were presented.

Experimental Loss Analyses in High-Specific-Speed Hydroturbines with Adjustable Blade Runner. 3rd Report, Runner Friction Losses and Friction Coefficients.

This third report deals with friction losses in adjustable blade runners for axial-flow hydroturbines. A method is proposed to extract the friction coefficient for the runner loss from the measured performance characteristics of bulb turbines. As a result of the loss analysis for two model bulb turbines based on the above method under a wide range of runner vane setting angles and wicket gate openings, an algorithm is presented for computing the friction loss in a runner using the well-established friction coefficient for a flat plate with the same Reynolds number and surface roughness as the blade at the root mean square radius.

A New Way of Plotting the Cylindrical Blade

A new way of plotting the cylindrical blade, shown in this paper, guarantees that the vane setting angle varies linearly and continuously smooth streamlines are thus obtained to avoid flow separation within the impeller channels. The blade contour is the solution to a differential equation in polar coordinates.

Effect of stay vane angle on the performance of hydraulic turbine.

The effects of stay vane angle on the turbine efficiency performance was investigated with a tandem circular cascade comprising stay vanes and wicket gates of a high specific speed Francis turbine. The velocity distributions around the stay various and wicket gates as wall as the variation of angular momentum along the streamline were calculated with the Flow analysis computer program based on the quasi-three dimensional Flow theory for the various combination of the stay vane setting angle and the wicket gate opening. A model Francis turbine having the same configurations of stay vane and wicket gate as those analyzed numerically was tested to measure the turbine efficiency and compare with the results of slow analysis. The measured results showed a good correlation with the calculated results and it made clear that the angle of stay vane affects the turbine efficiency in the region of large wicket gate opening.

Influence of Freely Rotating Inlet Guide Vanes on the Return Flows and Stable Operating Range of an Axial Flow Fan

This paper presents the results of experimental investigations on the three-dimensional flow and performance characteristics of a free vortex axial flow fan rotor, with a freely rotating and braked inlet guide vane row. The influences of axial distance between the inlet guide vane row and the rotor inlet, inlet guide vane setting angle and shape, partial omission of guide vanes at the hub and tip regions on the return flows have been studied and optimum axial distance and setting angle that will improve the useful operating range of the fan were determined. Use of freely rotating inlet guide vanes at high flow volumes and braked inlet guide vanes at low flow coefficients resulted in a reduction of return flows and an increase of the stable operating range of the axial fan rotor by more than 35 percent and this combination has yielded higher efficiencies as well in the extended region of stable operation.