Unsteady Flows In Turbomachines Research Articles

Past Developments and Current Advancements in Unsteady Pressure Measurements in Turbomachines

The aim of this paper is to review, summarize, and record long-term experience with development and application of aerodynamic probes with built-in miniature pressure transducers for unsteady pressure measurement and industrial research in turbomachine components. The focus of the first half of the paper is on the work performed at VZLU Prague, Czech Republic (Secs. 3–8). The latest development in unsteady pressure measurement techniques and data reduction methodology suitable for future research in highly loaded, high-speed turbine engine components performed at NASA GRC Cleveland, OH, is reported in Secs. 8–15 of this paper. Excellent reviews of similar activities at ETH Zürich, Switzerland by Kupferschmied, et al. (2000, “Time-Resolved Flow Measurements With Fast-Response Aerodynamic Probes in Turbomachines,” Meas. Sci. Technol., 11(7), pp. 1036–1054) and at VKI Rhode-Sain-Genèse, Belgium by Sieverding, et al. (2000, “Measurement Techniques for Unsteady Flows in Turbomachines,” Exp. Fluids, 28(4), pp. 285–321) were already reported and are acknowledged here. A short list of reported accomplishments achieved by other researchers at various laboratories is also reported for completeness. The authors apologize to those whose contributions are not reported here. It is just an unfortunate oversight, not an intentional omission.

1201 ターボ機械内部流の非定常性について : 主に空力特性への影響(OS12-1 流体機械の諸問題,オーガナイズドセッション)

Understanding and utilization of unsteadiness associated with the flow field in turbomachines is considered very important to develop breakthrough-technologies for more efficient and environment-friendly turbomachines. This report mainly describes what unsteady flows in turbomachines are and how those unsteadinesses affects the aerodynamic performance of the turbomachines in favorable and adverse manners, followed by the description on recent progresses of computational and experimental studies to control and exploit the unsteady flows.

Effect of inlet duct contour and lack thereof on the noise generated of an axial flow fan

This study concerns the unsteady flows in turbomachines in general, and the aeroacoustics of fans in particular. The principal objective of this paper is the determination of the influence of the upstream environment on the acoustic and aerodynamic behavior of axial fans. After analysis of the various sources of noise present in turbomachines, interest is focused on the influence of the disturbances of the velocity field at the suction. Accordingly, the effect of the presence of a contoured duct and a lack thereof at the inlet of an axial flow fan is analyzed . The results show the strong involvement of the upstream turbulence level in the generation of the noise, and in particular, of broadband noise.

Experimental investigation of turbulent wake–blade interaction in axial compressors

Abstract The fundamentally unsteady character of flow in multi-stage turbomachines is traditionally neglected in most of the flow calculation methods. The rapid development of hard- and software for numerical flow simulation has opened possibilities for investigation of the unsteady flow in turbomachines. The still existing methodical problems in the simulation especially of turbulent flow makes the experimental validation of numerical results indispensable. In a low-speed research axial compressor with incompressible flow conditions and relatively large geometric dimensions, a flow measuring system based on split-film probes has been installed and extensively operated. Measurements of the unsteady flow field and the turbulence properties concerning the blade wakes have been made and reported. In the subsequent investigation, the passage of the IGV wakes and the rotor blade wakes of the first rotor through the adjacent stator blade row have been explored in one measuring plane in front of the stator, four measuring planes within the stator and a measuring plane behind the stator at the mean radius of the blading. Measurements of the unsteady absolute velocity field in the S1-plane and the turbulent fluctuations have been made. The transportation of the IGV wake through the stator is one result of the measurements. The decay of the fluctuation components inside the stator blade row has been investigated in detail.

Measurement techniques for unsteady flows in turbomachines

The growing interest for unsteady flows in turbomachines over the last two decades has led to an intensive development of fast response measurement techniques, capable of resolving with high frequency phenomena related to inlet distortion, rotating stall and blade row interference effects with blade passing frequencies ranging from 3 to 30 kHz. This development was favoured by major advances in sensor technology and data acquisition systems. The paper reviews the progress in fast response measurement techniques for high speed turbomachinery and application with emphasis on fast response pressure and temperature probes and blade surface sensors including pressure, heat transfer and shear stress determination.

The Use of Hot-Wire Anemometry to Investigate Unsteady Wake-Induced Boundary-Layer Development on a High-Lift LP Turbine Cascade

Recent research has revealed positive effects of unsteady flow on the development of boundary layers in turbine cascades, especially at conditions with a laminar suction side separation bubble at low Reynolds numbers. Compared to steady flow, a reduction of total pressure loss coefficient over a broad range of Reynolds numbers has been shown. Taking into account the positive effects of wake-induced transition already during the design process, new high lift bladings with nearly the same low losses at unsteady inlet flow conditions could be achieved. This leads to a reduction of weight and cost of the whole turbine module for a constant stage loading. Unsteady flow in turbomachines is caused by the relative motion of rotor and stator rows. For simulating a moving blade row upstream of a linear cascade in the High-Speed Cascade Wind Tunnel of the Universita¨t der Bundeswehr Mu¨nchen, a wake generator has been designed and built. The wakes are generated with bars, moving with a velocity of up to 40 m/s in the test section upstream of the cascade inlet plane. Unsteady flow causes the transition on the surface of the suction side of a low-pressure turbine blade to move upstream whenever an incoming wake is present on the surface; moreover, a laminar separation bubble can be diminished or even suppressed. In order to detect the effects of wakes on the boundary layer development a new hot wire data acquisition system is required. Due to the fact that hot wires give a good insight into boundary layer development, a new hot-wire data acquisition system has been set up. The anemometry system can acquire four channels simultaneously, therefore being capable of logging a triple hot-wire sensor and a bar trigger simultaneously. One further channel is utilized for a once-per-revolution trigger. The once-per-revolution trigger is used to start the measurement of one data block. Using the well-established ensemble-averaging technique, 300 ensembles each consisting of five wake passing periods have been acquired. Ensemble averaging can be directly performed without any data reduction. The adaptation of this new hot-wire anemometry data acquisition system to the High-Speed Cascade Wind Tunnel of the Universita¨t der Bundeswehr Mu¨nchen is pointed out. First, results on unsteady periodic boundary layer development of a highly loaded low-pressure turbine cascade under unsteady inlet flow conditions are presented. During the present investigation four boundary layer traverses, ranging from x/lax=0.82 to x/lax=0.99 (suction side), at steady and unsteady inlet flow conditions Ubar=10 m/s at an outlet Reynolds number of Re2th=100,000 have been conducted. [S0889-504X(00)00204-X]

Unsteady turbomachinery flow simulations on massively parallel architectures

The accurate numerical simulation of unsteady, three-dimensional viscous flow in turbomachines is computationally very intensive, requiring prohibitively large amounts of computer time on current vector supercomputers. In recent years, computer systems based on massively parallel architectures have been developed that offer the promise of meeting the computational power requirements of such large-scale simulations. However, a rethinking of existing algorithms and methodology is required in order to fully harness the computational power of such architectures. In this paper the capabilities of the Connection Machine (CM-2) in predicting unsteady flows in turbomachines are evaluated. The implementation on the CM-2 of an implicit, time-accurate, zonal algorithm for the Navier-Stokes equations in two dimensions is described. Programming issues and modifications made to the original algorithm (developed for vector, pipelined supercomputers) in order to improve performance on the CM-2 are outlined. Algorithm performance is evaluated and compared with a functionally equivalent code for the CRAY-YMP.

Supercomputer Applications in Gas Turbine Flowfield Simulation

The numerical simulation of the unsteady, three-dimen sional, viscous flow in a gas turbine stage is considered. Results from a three-dimensional, time-accurate Navier- Stokes simulation of rotor-stator interaction in an axial turbine stage are presented. The present study uses a fine grid in the spanwise direction to better resolve the complex three-dimensional flowfield, and complements earlier reported coarse-grid calculations. Several different features of the flowfield are analyzed and compared to earlier calculations and to experimental data wherever possible. Computer animation techniques are used to visualize various unsteady, three-dimensional features of the flow. The results demonstrate the capabilities of cur rent computing hardware in obtaining accurate simula tions of unsteady flows in turbomachines.

Experimental Analysis Methods for Unsteady Flows in Turbomachines

This paper describes the measuring methods developed at the ONERA Aerodynamics Department for the characterization of unsteady flows in turbomachines. They mainly concern the flow in the rotor, its wake, and boundary layers on stator or rotor blades. The means used consist of: • measurements using pressure probes or short response time pressure transducers, • measurements with hot wire probes or hot film gauges, and • direct, measurements using laser velocimeter.

A Study on the Flow Visualization by the Hydrogen-Bubble Method.

In the investigations of both the steady and unsteady flow in turbomachines, it has been found to be highly successful to visualize the flow in ducts and around the bodies. Recently W. Clutter and O. Smith have presented a suitable technique for flow visualization using small hydrogen-bubbles produced by electrolysis of the working water itself. According to their experiments, unfortunately the method was not applied to the flow with higher velocity than about 0.6m/sec. In order to observe the stream lines flowing at about 5∼8m/sec in an axial-flow type testing water compressor, the authors improved the electric source and the working liquid in the hydrogen-bubble method, and developed several new probes which are inserted into the stream as cathodes for the electrolysis process and which consist of a straight or kinked platinum wire and fork-type brass stem. In a small water tunnel having a test section 60×200 mm and two observation windows on each side, direct current of high tension (2000volts) was charged between the probe and the tunnel duct and thereby the lines of hydrogen-bubbles generated from the probe wire were visible fairly well even in the higher velocity stream of about 7m/sec. Further, using the above mentioned method, some photographs of the rotating stalls occurring in the testing water compressor were taken successfuly as was expected.