scholarly journals Investigation of Unsteady Flow Phenomena in a Counterrotating Ducted Propfan

1998 ◽  
Author(s):  
L. Wallscheid ◽  
F. Eulitz ◽  
R. Heinecke
Keyword(s):  
Unsteady Flow ◽  
Total Pressure ◽  
Pressure Rise ◽  
Leading Edge ◽  
Pressure Waves ◽  
Pressure Measurements ◽  
Numerical Investigations ◽  
Downstream Effects ◽  
Flow Phenomena ◽  
Unsteady Simulation

Experimental and numerical investigations on a counterrotating propfan (CRISP) have been carried out to study unsteady flow phenomena generated by the interaction of the two rotors. This paper focuses mainly on the downstream effects of rotor 1 on rotor 2. Therefore unsteady Laser-2-Focus, unsteady total pressure measurements and an unsteady simulation have been carried out. The total pressure measurements behind the rotors show variations of the absolute total pressure outside the wake regions up to 30 percent of the average total pressure rise. Some of these are caused by the interaction of the rotor 1-generated wakes with the leading edge of rotor 2. The others may result from the pressure waves generated by the reflection of the rotor 2-shockwaves by the blades of rotor 1.

Flow Survey of a Forward Curved Blades Centrifugal Fan for HVAC Applications

2016 ◽  
Author(s):  
Fabio Breviario ◽  
Dario Brivio ◽  
Lucio Cardillo ◽  
Alessandro Corsini ◽  
Giovanni Delibra
Keyword(s):  
Total Pressure ◽  
Acoustic Emissions ◽  
Pressure Rise ◽  
Leading Edge ◽  
Cost Effective ◽  
Centrifugal Fan ◽  
Centrifugal Fans ◽  
Flow Features ◽  
Curved Blade ◽  
New Generation

The advancements in fan technology are nowadays animated by two major drivers: the legal requirements that impose minimum fan efficiency grades for fans sold within European Union (and soon US and Asia), and the market request for better air performance and lower sound emissions. Within HVAC (Heating, Ventilating and Air Conditioning) applications, centrifugal fans with forward curved blades are widely used due to the higher total pressure rise capability and lower acoustic emissions with respect to more efficient backward curved blades. However the continuous rise of minimum fan efficiency grades pushes the manufacturers to develop a new generation of forward curved centrifugal fans, improving previous design. Here the challenge is not only on aerodynamics, but in the overall production process, as squirrel cage fans are characterised by a cost-effective consolidated technology, based on simple blade geometries and easy series manufacturing. For example, the blades usually have circular camber lines, as results of cut cylinders. Thus, once the number of blades and the angle at the leading edge are selected, the chord and the deflection capability are constrained as well. These concurring aspects led industry to include in the design process new tools, in particular CFD, to analyse the flow features of the current generation of fans in order to understand which phenomena are to be either controlled or exploited to increase efficiency and total pressure rise. Here we present a numerical investigation on a forward curved blade centrifugal fan for HVAC applications, to highlight the flow features inside the impeller and in the critical region of coupling with the volute. The analysis was carried out with OpenFOAM, an open-source library for CFD. Computations were performed with the frozen rotor approach and validated against available experimental data.

Forward Sweep in a Four-Stage High-Speed Axial Compressor

2006 ◽  
Author(s):  
Michael Braun ◽  
Joerg R. Seume
Keyword(s):  
Total Pressure ◽  
High Speed ◽  
Axial Compressor ◽  
Pressure Rise ◽  
Leading Edge ◽  
Third Stage ◽  
Mach Number Distribution ◽  
Design Speed ◽  
End Wall ◽  
Operating Points

The present paper provides a comparison of a CDA-bladed four-stage high-speed axial compressor and a configuration in which the first three rows are replaced with forward swept blades and vanes. The blades are designed with sweep from mid-span to tip, the vanes from mid-span to the hub. The non-swept portion of the leading edge is kept radial and identical to the CDA blading. The overall performance of the compressor with both configurations is measured at five engine speeds. The flow fields of each rotor and stator at two operating points (“Design Point” and “Near Stall”) of both configurations are investigated at the design speed. On the suction and the pressure side of the third stage vane, static surface pressures are measured to determine the local Mach number distribution and to identify zones of separation. Multistage CFD-computations are carried out for both configurations. The numerical and experimental results of both configurations are compared and show the effect of sweep on the operating map of the compressor from choke to stall: Sweep reduces corner stall and the end-wall losses at high aerodynamic loads. It is shown that the reduction of separation due to sweep leads to an increase of total pressure rise towards lower mass flow so that the present swept compressor achieves higher total pressure ratios at and near the stall limit. An analysis along streamlines suggests that the performance of the compressor could have been improved further by a more uniform total pressure distribution in the front stages and a better match of the sweep in stages 2 and 3.

The Unsteady Flow and Forced Response for a Variable Nozzle Turbine

2013 ◽  
Vol 871 ◽  
pp. 296-303
Author(s):  
Yi Xiong Liu ◽  
Da Zhong Lao ◽  
Yin Hong Liu ◽  
Ce Yang ◽  
Chao Chen Ma
Keyword(s):  
Unsteady Flow ◽  
Dynamic Stress ◽  
Leading Edge ◽  
Element Model ◽  
Forced Response ◽  
Turbine Wheel ◽  
Order Resonance ◽  
Load Fluctuation ◽  
Unsteady Simulation ◽  
Nozzle Opening

Variable nozzle turbine (VNT) has become a popular technology for diesel application. While one of the major challenges for VNT is resonant vibration due to the fluctuating pressure in unsteady flow. Both the leakage flow forms inside the nozzle clearances and the shock produces under small nozzle openings increase the flow unsteadiness inside downstream rotor tunnel. In this paper, the unsteady simulation of the turbine was conducted to investigate the effects of nozzle clearances and openings on the transient load fluctuation of the blades. Then a finite element model of turbine wheel was built and blade forced response was simulated with harmonic analysis. The results showed that the decrease of nozzle opening would intensify rotor vibration and increase the blade dynamic stress. The simulation of blade resonance showed that the 1st order resonance located at the blade trailing edge while the 2nd order resonance happened at the leading edge, which was consistent with the blade actual crack.

Analysis of the Inter-Row Flow Field Within a Transonic Axial Compressor: Part 2 — Unsteady Flow Analysis

2000 ◽  
Author(s):  
Xavier Ottavy ◽  
Isabelle Trébinjac ◽  
André Vouillarmet
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Flow Analysis ◽  
Axial Compressor ◽  
Leading Edge ◽  
Rotor Blades ◽  
Time Averaging ◽  
Flow Phenomena ◽  
Order Of Magnitude ◽  
Transonic Axial Compressor

An analysis of the experimental data, obtained by laser two-focus anemometry in the IGV-rotor inter-row region of a transonic axial compressor, is presented with the aim of improving the understanding of the unsteady flow phenomena. A study of the IGV wakes and of the shock waves emanating from the leading edge of the rotor blades is proposed. Their interaction reveals the increase in magnitude of the wake passing through the moving shock. This result is highlighted by the streamwise evolution of the wake vorticity. Moreover, the results are analyzed in terms of a time averaging procedure and the purely time-dependent velocity fluctuations which occur are quantified. It may be concluded that they are of the same order of magnitude as the spatial terms for the inlet rotor flow field. That shows that the temporal fluctuations should be considered for the 3D rotor time-averaged simulations.

An Experimental Investigation of Stator Clocking Effects in a Two-Stage Low-Speed Axial Compressor

2011 ◽  
Author(s):  
J. Sta¨ding ◽  
D. Wulff ◽  
G. Kosyna ◽  
B. Becker ◽  
V. Gu¨mmer
Keyword(s):  
Total Pressure ◽  
Axial Compressor ◽  
Axial Flow ◽  
Leading Edge ◽  
Global Scale ◽  
Flow Coefficient ◽  
Maximum Efficiency ◽  
Pressure Measurements ◽  
Low Speed ◽  
The Impact

The impact of stator clocking on performance and flow of a 2.5-stage axial compressor has been investigated. Stator clocking, the circumferential indexing of adjacent stator rows with equal blade counts, is known as a potential means to modify the flow field in multistage turbomachinery and increase overall efficiencies of both turbines and compressors. These potential effects on turbomachine performance are due to wake-airfoil interactions and primarily depend on the alignment of the downstream stator row with the upstream stator wake path. The present survey describes and discusses the experimental research on stator clocking effects in a low-speed 2.5-stage axial flow compressor, using front loaded CDA blade sections and cantilevered stator rows with identical blade counts. Conventional static pressure tappings were used to locate global peaks in compressor performance for varying Stator 2 clocking positions at different flow coefficients. Results of unsteady total pressure measurements obtained by means of a high-frequency pressure transducer, embedded in the Stator 2 leading edge, give information on Stator 1 wake propagation. Traverse data from pneumatic 5-hole probes show the impact of stator indexing on Stator 2 exit total pressure at different blade spans. Regardless of flow coefficient, the variations of overall compressor efficiency due to Stator 2 clocking are around 0.2% and are exhibiting a near-sinusoidal trend over the clocking angle. It is shown that total pressure measurements at mid-span of Stator 2 leading edge suggest best overall performances for design and low loading conditions, if the Stator 1 wakes pass through mid-passage of Stator 2. At high loading, however, maximum efficiency locates the wake path directly at the leading edge. Due to a considerable span-wise skewness of the upstream stator wake, the aerodynamic clocking position for Stator 2 varies from hub to tip. While it is shown again that this effect weakens the advantages of airfoil indexing on a global scale, stator clocking shows much more potential if only a single blade section is considered.

Strut Influences Within a Diffusing Annular S-Shaped Duct

1998 ◽  
Author(s):  
G. Norris ◽  
R. G. Dominy ◽  
A. D. Smith
Keyword(s):  
Gas Turbines ◽  
Total Pressure ◽  
Pressure Measurements ◽  
Computational Results ◽  
Flow Conditions ◽  
Test Rig ◽  
General Flow ◽  
Flow Phenomena ◽  
Physical Features ◽  
Cooling Air

Inter-turbine diffusers which provide flow continuity between the H.P. and L.P. turbines, are increasingly important within modern aero gas turbines, as the fan and hence L.P. turbine diameters increase with thrust. These gas turbines rely on struts within the inter-turbine diffuser to serve both as load bearing supports for inner spools and as passages to supply the engine with vital services such as cooling air and lubrication oil. Experimental measurements have been made on a representative test rig in order to investigate the affect of a ring of struts on both the local and general flow phenomena as well as investigating their effect on overall duct performance. More realistic flow conditions are made available by the use of inlet wakes representative of those created by an upstream turbine row. Measurements include static pressures on the strut and duct surfaces along with velocity and total pressure measurements at various axial locations. From these results calculations of total pressure loss have been made. The experimental results presented in this paper have been used to validate C.F.D. flow predictions on the duct with and without struts. The computational results included, capture the main physical features of the flow but clear limitations are observed and are discussed in this paper.

scholarly journals Rotor–Stator Interaction in a Diffuser Pump

1989 ◽  
Vol 111 (3) ◽  
pp. 213-221 ◽  
Author(s):  
N. Arndt ◽  
A. J. Acosta ◽  
C. E. Brennen ◽  
T. K. Caughey
Keyword(s):  
Pressure Fluctuations ◽  
Pressure Rise ◽  
Leading Edge ◽  
Suction Side ◽  
Pressure Measurements ◽  
Vaneless Diffuser ◽  
Impeller Blade ◽  
Frequency Spectra ◽  
Vaned Diffuser ◽  
Wall Pressure Fluctuations

The interaction between impeller blades and diffuser vanes in a diffuser pump was investigated. Steady and unsteady pressure measurements were taken on the diffuser vanes, and the shroud wall of a vaned and a vaneless diffuser. Steady, unsteady, and ensemble-averaged unsteady data, as well as frequency spectra, are presented. The measurements were made for different flow coefficients, shaft speeds, and radial gaps between impeller blade trailing and diffuser vane leading edge (1.5 and 4.5 percent based on impeller discharge radius). The resulting lift on the vane, both steady and unsteady, was computed from the pressure measurements at midvane height. The magnitude of the fluctuating lift was found to be greater than the steady lift. The pressure fluctuations were larger on the suction side than on the pressure side attaining their maximum value, of the same order of magnitude as the total pressure rise across the pump, near the leading edge. Pressure fluctuations were also measured across the span of the vane, and those near the shroud were significantly smaller than those near the hub. The pressure fluctuations on the shroud wall itself were larger for the vaned diffuser than a vaneless diffuser. Lift, vane pressure, and shroud wall pressure fluctuations decreased strongly with increasing radial gap.

scholarly journals An experimental investigation on the interaction between inlet swirl distortion and a low-speed axial compressor

2020 ◽  
Vol 103 (3) ◽  
pp. 003685042094092
Author(s):  
Xuegao Wang ◽  
Jun Hu ◽  
Jin Guo ◽  
Baofeng Tu ◽  
Zhiqiang Wang
Keyword(s):  
Experimental Investigation ◽  
Axial Velocity ◽  
Total Pressure ◽  
Axial Compressor ◽  
Pressure Rise ◽  
Leading Edge ◽  
Low Speed ◽  
Performance Change ◽  
Inlet Swirl ◽  
Compressor Performance

The aim of this article mainly lies in two aspects. The first is to investigate the effect of inlet swirl distortion on the performance and stability of a low-speed compressor experimentally. The second is to quantify swirl pattern revolution through the compressor and find out background causes of the change in compressor performance. Swirl distortion makes the leading-edge incidence opposite between tip and hub regions, compared to that of clean flow. And the compressor performance change is ultimately determined by these two aspects. Results indicate that negative bulk swirl improves pressure rise, and the effect is on the contrary to the positive bulk swirl. Under the condition of paired swirl, pressure rise also presents a reduction. All these three types of swirl have little effect on the stall boundary. Although swirl distortion shows clear recovery at rotor exit, downstream components still work at off-design conditions due to the induced nonuniformity in axial velocity and total pressure.

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