04-07-2012, 10:37 AM
Patented Hollow Blades of the Axial Fan with Trailing Edge Self-Induced
Blowing
Patented Hollow Blades.pdf (Size: 270.64 KB / Downloads: 52)
Abstract:
Axial fans often show adverse flow conditions at the fan hub and at the tip of the blades. In the present paper, a
modification of conventional axial fan blades with experimental investigation is presented. Patented hollow blades were
manufactured from the hub to the trailing edge at the tip of the blades. They enable the formation of self-induced internal
flow through internal passages. The internal flow enters the internal radial flow passages of the hollow blades through the
openings near the fan hub and exits through the trailing edge slots at the tip of the blade. The influence of internal flow on
the flow field of axial fan and the modifications of aerodynamic characteristics of the axial fan have been studied along
with recent patents.
INTRODUCTION
Axial fans often show adverse flow conditions at the fan
hub and at the tip of the blades [1]. Near the axial fan hub, at
the location of the inlet slot, recirculation flow occurs. Here,
the attachment of the blade onto the fan motor is optimized
for easy manufacturing, which affects aerodynamic
properties. Consequently, a decrease in flow velocity and
increase in pressure are present. As a result, radial flow,
passing from the hub to the tip of the blade has negative
effects on the fan efficiency. Across the entire blade, the
separation of flow on the suction side of the blade occurs.
External flow is not able to follow the path of the blades'
profile; therefore it separates from the profile. The thickness
of the boundary-layer is increased.
EXPERIMENTAL SET-UP
To confirm the above assumptions, two versions were
compared differing only in the presence or absence of
internal flow through the blade. Measurements of the
aerodynamic characteristic and efficiency were performed.
All measurements were performed at equal operating and
known ambient conditions. The results show that the
introduction of internal flow improved the fan characteristics
and reduced the flow separation on the suction side of the
blade. The increase of axial fan efficiency due to the
introduction of internal flow also points to a more interesting
technical solution offering possibilities for new types of
applications.
AERODYNAMIC CHARACTERISTIC MEASUREMENTS
AND RESULTS FOR THE AXIAL FAN WITH
HOLLOW BLADES
The experiments on the axial fan with hollow blades
were conducted on a specially designed test station for the
measurements of aerodynamic characteristics [3].
Measurements were performed for versions both with and
without internal flow. To obtain comparable results, the
aerodynamic characteristic measurements were performed in
accordance with the standard [14] at equal operating and
ambient conditions and at the same fan operating points. The
main sources of total measurement uncertainty [15] are the
uncertainty of measuring rotating frequency, volume flow,
pressure difference, temperature correction, humidity, etc.
Overall measuring uncertainty is estimated to 2.8% of the
measured value and is in accordance with standard [14].
WIND TUNNEL MEASUREMENTS
The purpose of the measurement on the hollow airfoil in
the low-speed wind tunnel is to confirm the influence of two
flows interacting with the flow field near the trailing edge of
the hollow airfoil, and, consequently, to better understand
the changes occurring to the aerodynamic characteristic of
the developed axial fan with hollow blades.
RECENT PATENTS
A recent method for making a hollow fan blade including
the steps of: a) forming a plurality of ribs, on a first
substrate, including cavities on either side of each of the
plurality of ribs; b) abutting the plurality of ribs on the first
substrate with a second substrate to form a hollow fan blade;
c) forming the hollow fan blade into an airfoil shape while
pressure inside the cavities is substantially ambient pressure
has been patented, that generally relates to gas turbine
engines and more particularly to an improved hollow fan
blade for a gas turbine engine [18]. Another patent discloses
a method for making a hollow fan blade including the steps
of: a) machining a plurality of continuous cavities on a first
substrate to define a plurality of ribs adjacent the cavities.