Reversing of Axial Flow Fans for Ventilation

2011 ◽  
Author(s):  
Vaclav Cyrus ◽  
Jiri Pelnar ◽  
Jan Cyrus
Keyword(s):  
Volume Flow Rate ◽  
Flow Direction ◽  
Pressure Coefficient ◽  
Axial Flow ◽  
Aerodynamic Performance ◽  
Flow Reversal ◽  
Design Flow ◽  
Flow Coefficient ◽  
Final Decision ◽  
Flow Mechanism

Changing the flow direction in fans is frequently required in emergency situations in traffic tunnels, chemical plants and mines ventilation. Reverse flow in axial flow fan is often achieved using two methods: a) Changing direction of fan rotation and turning the stator vanes (Method I). b) Turning / resetting rotor blades during fan rotation (Method II). The required volume flow rate at flow reversal is usually at least 60% valid for normal fan working point. The motivation of the present paper is to compare the aerodynamic performance and 3D flow mechanism in fan stage at flow reversal carried out by the two methods above. In our paper conditions of the flow reversal are discussed. Theoretical relations are derived for both methods using fundamental equations valid for internal aerodynamics of axial flow compressors and fans. Parameters of three fan axial stages were measured on a 600 diameter test rig at standard and reverse conditions. The investigated fan ventilation stages had a design flow coefficient of 0.35 to 0.40 and pressure coefficient of 0.30. Flow field measurements were carried out with the use of 5-hole pressure probes in the stage planes. The blade rows flow mechanism at the standard and reverse conditions is described using test data obtained for both flow reversal methods. The flow simulation results were also used. It has been found in our investigations that moderate aerodynamic loading of the ventilation fans has better aerodynamic performance during flow reversal if Method II is used. Fan designers and users making the final decision relating to the selection of the flow reversal method should also include the reliability and cost of the reverse fan design with blade turning mechanism.

Aerodynamic Performance of an Axial Compressor Stage With Variable Rotor Blades and Variable Inlet Guide Vanes

1998 ◽  
Author(s):  
Václav Cyrus
Keyword(s):  
Volume Flow Rate ◽  
Pressure Coefficient ◽  
Axial Flow ◽  
Aerodynamic Performance ◽  
Rotating Stall ◽  
Rotor Blades ◽  
Flow Coefficient ◽  
Experimental Investigations ◽  
Compressor Stage ◽  
Flow Stage

Experimental investigations of flow fields and losses in an axial flow compressor stage were carried out. The stage has hub/tip ratio of 0.7. The design values of flow coefficient and pressure coefficient are 0.6 and 0.81, respectively. Aerodynamic performance was investigated for two principal configurations: i) axial flow stage with variable rotor blades, ii) axial flow stage with variable inlet guide and stator vanes. The most efficient volume flow rate regulation of the stage was with the application of variable rotor blades. On the basis of experimental data an analysis of the origin of flow separation on the suction and pressure surfaces of rotor and stator blades was made with the use of simple design criteria. The unsteady flow of rotating stall type in the tested stage appeared after simultaneous occurence of large stall regions in both rotor and stator blade rows. The existence of large stall regions in the IGV did not affect the rotating stall onset. At high values of the IGV stagger angle change (50 deg) pressure pulsations appeared due to the occurence of stall.

Axial Fan at Reversal Flow

2004 ◽  
Author(s):  
Va´clav Cyrus
Keyword(s):  
Volume Flow Rate ◽  
Axial Flow ◽  
Volume Flow ◽  
Design Flow ◽  
Flow Coefficient ◽  
Flow Rate Ratio ◽  
External Diameter ◽  
Axial Fan ◽  
Aerodynamic Loading ◽  
Reversal Flow

Flow reversal in axial fans is usually performed by the change of revolution direction and by stator vanes turning. Derived relations express the relative position of characteristics curves for reverse and normal flows. The ratio of volume flow rates at these conditions decreases with rotor blade profiles camber (aerodynamic loading) and with flow coefficient. The characteristics of two axial-flow stages A, B with different aerodynamic loading and design flow coefficient were measured on a test rig with external diameter of 600mm. Rotor diffusion factor D at mid-span of stage A and B were DR,m = 0.56 and DR,m = 0.3. Design flow coefficient was φD = 0.6 and 0.4, respectively. Theoretical deductions were confirmed by the experiment. Required volume flow rate ratio (Qrev/Qn ≥ 0.6) was reached only in the case of stage B. Detailed flow fields investigations were carried out in this case with the use of 5-hole conical probes at normal and reverse flows. The mechanism of 3D flows in blade rows could be described in these different fan working regimes.

The Measurement and Interpretation of Flow within Rotating Stall Cells in Axial Compressors

1978 ◽  
Vol 20 (2) ◽  
pp. 101-114 ◽  
Author(s):  
I. J. Day ◽  
N.A. Cumpsty
Keyword(s):  
Flow Direction ◽  
Axial Flow ◽  
Tangential Direction ◽  
Rotating Stall ◽  
Design Flow ◽  
Flow Measurements ◽  
Axial Compressors ◽  
Multi Stage ◽  
Wide Range ◽  
Flow Compressor

Detailed flow measurements obtained by a new measuring technique are presented for the flow in a stalled axial-flow compressor. Results were obtained from a wide range of compressor builds, including multi-stage and single-stage configurations of various design flow rates and degrees of reaction. Instantaneous recordings of absolute velocity, flow direction and total and static pressures have been included for both full-span and part-span stall. With the aid of these results, it has been shown that the conventional model of the flow in a stall cell is erroneous. An alternative model is proposed, based on the observation that the fluid must cross from one side of the cell to the other in order to preserve continuity in the tangential direction. An investigation of the experimental results also reveals the finer details of the flow in the cell and shows how these details are related to the design flow rate of the compressor. The influence of these cell details on the power absorbed by a stalled compressor are investigated, and consideration is given to the complex pressure patterns encountered in the compressor.

Effect of Tip Vortex Reduction on Air-Cooled Condenser Axial Flow Fan Performance: An Experimental Investigation

2021 ◽  
Author(s):  
J. P. Pretorius ◽  
J. A. Erasmus
Keyword(s):  
Performance Test ◽  
Performance Enhancement ◽  
Large Diameter ◽  
Pressure Coefficient ◽  
Axial Flow ◽  
Tip Clearance ◽  
Flow Coefficient ◽  
Tip Vortex ◽  
Experimental Investigations ◽  
Fan Performance

Abstract Large diameter axial flow fans are used in Air-cooled Condenser (ACC) systems of modern power stations. Efficiency improvements on these fans can significantly reduce the ACC power consumption and increase the net sent-out power to the grid. This study targets fan performance enhancement through blade tip vortex reduction. Experimental investigations are performed on a representative ACC scale fan, where tests consider the effects of tip clearance and two new tip endplate designs on fan performance. Test results confirm the findings of previous studies, showing the negative effect of increasing tip clearance on performance. Despite testing limitations, results from tests incorporating endplates show fan static pressure coefficient and efficiency increases over large ranges of flow coefficient compared to the datum fan. These outcomes agree with observations from literature and warrants further exploration. Future work is recommended to provide confirmation on the presented trends.

Wake–Boundary Layer Interactions in an Axial Flow Turbine Rotor at Off-Design Conditions

1989 ◽  
Vol 111 (2) ◽  
pp. 181-192 ◽  
Author(s):  
H. P. Hodson ◽  
J. S. Addison
Keyword(s):  
Rotor Blade ◽  
Axial Flow ◽  
Leading Edge ◽  
Surface Flow ◽  
Design Flow ◽  
Flow Coefficient ◽  
Experimental Investigations ◽  
Pressure Side ◽  
Suction Surface ◽  
Edge Separation

A series of experimental investigations has been undertaken in a single-stage low-speed turbine. The measurements involved rotor blade surface flow visualization, surface-mounted hot-film anemometry, and exit pitot traverses. The effects of varying the flow coefficient and Reynolds number upon the performance of the rotor blade at midspan are described. At the design flow coefficient (φ = 0.495), the rotor pressure surface flow may be regarded as laminar, while on the suction surface, laminar flow gives way to unsteady stator wake-induced transition and then to turbulent flow. Over the range of Reynolds numbers investigated (1.8×105–3.3×105), the rotor midspan performance is dominated by the suction surface transition process; suction surface separation is prevented and the rotor midspan loss coefficient remains approximately constant throughout the range. At positive incidence, suction surface leading edge separation and transition are caused by a velocity overspeed. Reattachment occurs as the flow begins to accelerate toward the throat. The loss associated with the separation becomes significant with increasing incidence. At negative incidence, a velocity overspeed causes leading edge separation of the pressure side boundary layers. Reattachment generally occurs without full transition. The suction surface flow is virtually unaffected. Therefore, the rotor midspan profile loss remains unchanged from the zero incidence value until pressure side stall occurs.

Effect of Circumferential Inlet Flow Distortion and Swirl on the Flow Field of an Axial Flow Fan Stage

1996 ◽  
Author(s):  
K. Viswanath ◽  
M. Govardhan
Keyword(s):  
Flow Field ◽  
Axial Flow ◽  
Design Flow ◽  
Flow Coefficient ◽  
Pressure Probe ◽  
Axial Flow Fan ◽  
Flow Distortion ◽  
Inlet Flow ◽  
Hole Pressure ◽  
Inlet Flow Distortion

This paper reports a study of the combined effects of swirl and circumferential inlet flow distortion on the flow field of an axial flow fan stage. The study involves steady state measurements of the flow field at the rotor inlet, exit and the stator exit of the single stage axial flow fan subjected to circumferential inlet flow distortion and swirl. Flow field survey was done at two flow coefficients, namely, ϕ = 0.45 and ϕ = 0.285. The flow at the inlet to the rotor was measured using a three hole pressure probe and five hole pressure probes were used at the rotor and stator exits. The study indicated that at the design flow coefficient swirl had caused deterioration of the performance in addition to that caused by distortion. In addition, the attenuation of distortion was high in the presence of swirl.

Modified Surge in an Axial Flow Compressor

1992 ◽  
Author(s):  
Libor Půst
Keyword(s):  
Experimental Study ◽  
Unsteady Flow ◽  
Axial Flow ◽  
Rotating Stall ◽  
Design Flow ◽  
Flow Coefficient ◽  
Axial Flow Compressor ◽  
Flow Compressor

This paper deals with an experimental study of the unsteady flow in a multistage axial-flow compressor with a high design flow coefficient (p = 1.2) at rpm lower than the design ones. A detailed description of the rotating stall during the so-called “modified surge” is given. In this surge type the rotating stall exists during all the surge cycle, in contradistinction of classic surge, when the rotating stall exists only in a part of the surge cycle.

Effect of Tip Vortex Reduction on Air-Cooled Condenser Axial Flow Fan Performance: an Experimental Investigation

2021 ◽  
pp. 1-28
Author(s):  
J.P. Pretorius ◽  
Johan A Erasmus
Keyword(s):  
Performance Test ◽  
Performance Enhancement ◽  
Large Diameter ◽  
Pressure Coefficient ◽  
Axial Flow ◽  
Tip Clearance ◽  
Flow Coefficient ◽  
Tip Vortex ◽  
Experimental Investigations ◽  
Fan Performance

Abstract Large diameter axial flow fans are used in Air-cooled Condenser (ACC) systems of modern power stations. Efficiency improvements on these fans can significantly reduce the ACC power consumption and increase the net sent-out power to the grid. This study targets fan performance enhancement through blade tip vortex reduction. Experimental investigations are performed on a representative ACC scale fan, where tests consider the effects of tip clearance and two new tip endplate designs on fan performance. Test results confirm the findings of previous studies, showing the negative effect of increasing tip clearance on performance. Despite testing limitations, results from tests incorporating endplates show fan static pressure coefficient and efficiency increases over large ranges of flow coefficient compared to the datum fan. These outcomes agree with observations from literature and warrants further exploration. Future work is recommended to provide confirmation on the presented trends.

Aerodynamic Performance of Advanced Axial Flow Fan for Power Industry Within its Operational Range

2014 ◽  
Author(s):  
V. Cyrus ◽  
J. Cyrus ◽  
P. Wurst ◽  
P. Panek
Keyword(s):  
Flow Separation ◽  
Three Dimensional ◽  
Axial Flow ◽  
Aerodynamic Performance ◽  
Rotor Blades ◽  
Design Flow ◽  
Axial Flow Fan ◽  
Angle Variation ◽  
Inlet Conditions ◽  
Inlet Chamber

The investigated axial flow fan investigated in our paper consisted of an advanced axial flow stage, an inlet chamber and a diffuser. The fan stage with high aerodynamic loading and the hub/tip ratio of 0.6 had the design flow and pressure coefficients of 0.60 and 0.83, respectively. The test and computed CFD aerodynamic performance of the axial flow fan and the fan’s stage were compared, with acceptable results. Subsequently, analysis of the computed 3D flow was carried out within the wide working range at the rotor blades stagger angle variation of ±20°.Consequence of the rotor blades adjustment is that the blade elements work often at the off-design working conditions with the flow separation on the blades suction and pressure sides. The flow is strictly three-dimensional. Velocity profile distortion and swirl due to the flow separation in the stator blade row decreases the diffuser pressure recovery and efficiency. The diffuser in the axial flow fan environment achieves a significantly higher efficiency in comparison with conical diffuser furnished with ducted-flow inlet conditions due to the increased turbulent mixing. Inlet chamber loss coefficient slightly decreased with the increasing flow rates due to the Reynolds number effect. Core flow in the inlet chamber is without occurrence of significant vortex inducing motion with the exception of the area near the tube where the fan’s shaft is located.

Fan Performance Scaling With Inlet Distortions

2018 ◽  
Vol 140 (7) ◽  
Author(s):  
J. J. Defoe ◽  
M. Etemadi ◽  
D. K. Hall
Keyword(s):  
Design Flow ◽  
Flow Coefficient ◽  
Axial Fan ◽  
Fan Performance ◽  
Physical Mechanisms ◽  
Viscous Losses ◽  
Performance Scaling ◽  
Large Distortion ◽  
Stator Blade ◽  
Primary Focus

Applications such as boundary-layer-ingesting (BLI) fans and compressors in turboprop engines require continuous operation with distorted inflow. A low-speed axial fan with incompressible flow is studied in this paper. The objectives are to (1) identify the physical mechanisms which govern the fan response to inflow distortions and (2) determine how fan performance scales as the type and severity of inlet distortion varies at the design flow coefficient. A distributed source term approach to modeling the rotor and stator blade rows is used in numerical simulations in this paper. The model does not include viscous losses so that changes in diffusion factor are the primary focus. Distortions in stagnation pressure and temperature as well as swirl are considered. The key findings are that unless sharp pitchwise gradients in the diffusion response, strong radial flows, or very large distortion magnitudes are present, the response of the blade rows for strong distortions can be predicted by scaling up the response to a weaker distortion. In addition, the response to distortions which are composed of nonuniformities in several inlet quantities can be predicted by summing up the responses to the constituent distortions.

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