Lip Separation and Inlet Flow Distortion Control in Ducted Fans Used in VTOL Systems

2014 ◽  
Author(s):  
Ali Akturk ◽  
Cengiz Camcı
Keyword(s):  
Angle Of Attack ◽  
Axial Flow ◽  
Vertical Force ◽  
High Angle ◽  
Flow Distortion ◽  
High Angle Of Attack ◽  
Inlet Flow ◽  
Flight Velocity ◽  
Ducted Fan ◽  
Inlet Flow Distortion

This paper describes a novel ducted fan inlet flow conditioning concept that will significantly improve the performance and controllability of ducted fan systems operating at high angle of attack. High angle of attack operation of ducted fans is very common in VTOL (vertical take off and landing) UAV systems. The new concept that will significantly reduce the inlet lip separation related performance penalties in the edgewise/forward flight zone is named DOUBLE DUCTED FAN (DDF). The current concept uses a secondary stationary duct system to control inlet lip separation related momentum deficit at the inlet of the fan rotor occurring at elevated edgewise flight velocities. The DDF is self-adjusting in a wide edgewise flight velocity range and its corrective aerodynamic effect becomes more pronounced with increasing flight velocity due to its inherent design properties. Most axial flow fans are designed for an axial inlet flow with zero or minimal inlet flow distortion. The DDF concept is proven to be an effective way of dealing with inlet flow distortions occurring near the lip section of any axial flow fan system, especially at high angle of attack. In this present paper, a conventional baseline duct without any lip separation control feature is compared to two different double ducted fans named DDF CASE-A and DDF CASE-B via 3D, viscous and turbulent flow computational analysis. Both hover and edgewise flight conditions are considered. Significant relative improvements from DDF CASE-A and DDF CASE-B are in the areas of vertical force (thrust) enhancement, nose-up pitching moment control and recovery of fan through-flow mass flow rate in a wide horizontal flight range.

scholarly journals Simulating the Effect of Wind on the Performance of Axial Flow Fans in Air-Cooled Steam Condenser Systems

2015 ◽  
Vol 7 (2) ◽  
Author(s):  
Neil Fourie ◽  
S. J. van der Spuy ◽  
T. W. von Backström
Keyword(s):  
Wind Velocity ◽  
Symmetry Plane ◽  
Axial Flow ◽  
Power Industry ◽  
Experimental Investigations ◽  
Flow Conditions ◽  
Flow Distortion ◽  
Inlet Flow ◽  
Wind Velocities ◽  
Inlet Flow Distortion

The use of air-cooled steam condensers (ACSCs) is preferred in the chemical and power industry due to their ability to adhere to stringent environmental and water use regulations. ACSC performance is, however, highly dependent on the prevailing wind conditions. Research has shown that the presence of wind reduces the performance of ACSCs. It has been found that cross-winds (wind perpendicular to the longest side of the ACSC) cause distorted inlet flow conditions, particularly at the upstream peripheral fans near the symmetry plane of the ACSC. These fans are subjected to what is referred to as “two-dimensional” wind conditions, which are characterized by flow separation on the upstream edge of the fan inlets. Experimental investigations into inlet flow distortion have simulated these conditions by varying the fan platform height. Low platform heights resulted in higher levels of inlet flow distortion, as also found to exist with high cross-wind velocities. The similarity between platform height and cross-wind velocity is investigated in this study by conducting experimental and numerical investigations into the effect of distorted inlet flow conditions on the performance of various fan configurations (representative of configurations used in the South-African power industry). A correlation between system volumetric effectiveness, platform height, and cross-wind velocity is derived which provides a means to compare platform height and cross-wind velocity effects.

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.

scholarly journals An Improved Integral Method for Prediction of Distorted Inlet Flow Propagation in Axial Compressor

2005 ◽  
Vol 2005 (2) ◽  
pp. 117-127
Author(s):  
Eddie Yin-Kwee Ng ◽  
Ningyu Liu ◽  
Hong Ngiap Lim ◽  
Daniel Tan
Keyword(s):  
Integral Method ◽  
Axial Compressor ◽  
Axial Flow ◽  
Quantitative Prediction ◽  
Flow Distortion ◽  
Inlet Flow ◽  
Flow Parameters ◽  
Inlet Flow Distortion ◽  
Flow Compressor ◽  
Flow Propagation

An improved integral method is proposed and developed for the quantitative prediction of distorted inlet flow propagation through axial compressor. The novel integral method is formulated using more appropriate and practical airfoil characteristics, with less assumptions needed for derivation. The results indicate that the original integral method (Kim et al., 1996) underestimated the propagation of inlet flow distortion. The effects of inlet flow parameters on the propagation of inlet distortions as well as on the compressor performance and characteristic are simulated and analyzed. From the viewpoint of compressor efficiency, the propagation of inlet flow distortion is further described using a compressor critical performance and its associated critical characteristic. The results present a realistic physical insight to an axial-flow compressor behavior with a propagation of inlet distortion.

Using Computational Fluid Dynamics to Simulate Multiple Axial Flow Fans in Air-Cooled Steam Condensers

2011 ◽  
Author(s):  
S. J. van der Spuy ◽  
T. W. von Backstro¨m ◽  
D. G. Kro¨ger
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Flow Field ◽  
Axial Flow ◽  
Test Facility ◽  
Pressure Jump ◽  
Flow Distortion ◽  
Inlet Flow ◽  
Actuator Disc ◽  
Inlet Flow Distortion

The large number of axial flow fans used in modern dry-cooled power plant air-cooled steam condensers necessitates the use of simplified numerical models when simulating the perfromance of such a condenser. Three simplified fan models are presented and implemented using computational fluid dynamics (CFD). These are referred to as the pressure jump, actuator disc and extended actuator disc models. The paper compares the CFD results obtained using these three models to experimental results obtained on a multiple axial flow fan test facility. The test facility was configured in such a way that it could accommodate different fan platform heights to vary the level of inlet flow distortion for the facility. The simulations show that the general flow field adjacent to the facility is independent of the simplified fan model that is used in the CFD analysis. However, the predicted flow field directly upstream of the edge fan varies according to the method used to represent the fan. It is also found that the more sophisticated fan models give a more accurate estimate of fan operation at higher levels of inlet flow distortion than the less sophisticated fan models.

Installed F/A-18 inlet flow calculations at a high angle of attack

1994 ◽  
Vol 10 (1) ◽  
pp. 110-115 ◽  
Author(s):  
James E. Bruns ◽  
C. Frederic Smith
Keyword(s):  
Angle Of Attack ◽  
High Angle ◽  
High Angle Of Attack ◽  
Inlet Flow
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