FAN AND FAN BLADES

Abstract

A fan blade (1) has a front leading edge (2) and a rear trailing edge (3). The fan blade (1) has a leading edge (4), at least some portions, that are undulated. The edge forms a wave (W) with a specific three-dimensional waveform.

Claims

1-13. (canceled)

14. A fan blade for a centrifugal fan comprises a leading edge and a trailing edge, the fan blade has a undulated leading edge, at least in a partial region, with a periodically repeating waveform, of period length λ, which deviates from a sinusoidal or almost sinusoidal waveform, in particular deviates from a sinusoidal or almost sinusoidal waveform with the same period length λ, the repeating waveform per period has at least one trough with two wave flanks running towards one another and each at an angle to the direction of flow and the undulated flanks extend at a steep tangential angle at or near their flank center relative to the direction of flow and, in comparison to a sinusoidal waveform, have steeper flanks in relation to the direction of flow.

15. The fan blade of claim 14, wherein the undulated leading edge has two or more periodically repeating waveforms.

16. The fan blade of claim 14, wherein the peak-to-trough value H of the wave measured from the front edge in the region of the undulated leading edge to the wave trough, as viewed in the flow direction, has values in relation to the period length λ, that are in the range 0.2≤λ/H≤2, the values can vary along the leading edge.

17. The fan blade of claim 14, wherein the fan blade has a chord length SL in particular in the region of the undulated leading edge and the peak-trough value H in the region of the wave troughs is preferably about 10%-30% of the chord length SL, more preferably 10% to 20% of the chord length SL.

18. The fan blade of claim 14, wherein in the repeating waveform per period forms two adjacent wave troughs between two wave flanks running towards one another at an angle to the direction of flow with a wave crest lying between the two wave troughs, which extends counter to the flow direction in the direction of the inflow-side front edge.

19. The fan blade of claim 14, wherein the obliquely running wave flanks extend, in or near their flank center relative to the direction of flow, at a tangential angle β between 15° and 35°, preferably at a tangential angle β between 25° and 30°.

20. The fan blade of claim 18, wherein the peak-to-trough value of the wave of the wave crest, which lies directly between two adjacent wave troughs, is approximately 10% to 80% of the peak-to-trough value of the immediately adjacent wave crest(s).

21. The fan blade of claim 18, wherein the undulated leading edge protrudes counter to the direction of flow relative to the leading edge in the non-undulated region, at least in regions of existing crests.

22. The fan blade of claim 18, wherein the blade profile, viewed at least in a profile section in the region of a wave crest, has a bulge protruding from the pressure side and a dent on the corresponding opposite position of the suction side, the surface profile is defined in such a way that the surface curvature changes twice when viewed in the direction of flow.

23. The fan blade of claim 14, wherein the blade profile viewed in a profile section at the front in the region of the leading edge curves further towards the suction side compared to one or the adjoining adjacent region that is less curved towards the suction side, preferably at a distance of one period, more preferably from period center to period center.

24. The fan blade of claim 14, wherein the fan blade is porous at least in portions in the region of the leading edge preferably with a connection from the pressure side to the suction side, such as by a plurality of channels passing through the fan blade.

25. A centrifugal fan having one or more fan blades of claim 14.

Description

BRIEF DESCRIPTION

[0036] FIG. 1 is an enlarged perspective view of a fan blade with an undulated leading edge in portions;

[0037] FIG. 2 is a detailed cross-section view of a profile section B through the fan blade in the crest of the leading edge wave to explain the S-shape;

[0038] FIG. 3 is a schematic view of a sine wave form of a wave at the leading edge and a wave form modified relative thereto, that runs through support points of the sine wave, in a variant with reversal points and a deeper incised wave trough;

[0039] FIG. 4 is a schematic view of a sine waveform of a wave at the leading edge and a modified waveform that runs through support points of the sine wave, in a variant with an additional crest in the center of the wave;

[0040] FIG. 5 is a detailed cross-section view of the profile section C through the fan blade according to FIG. 1;

[0041] FIG. 6 is a perspective view of an exemplary centrifugal fan with seven fan blades.

DETAILED DESCRIPTION

[0042] The disclosure is explained in more detail in the following using an exemplary embodiment with reference to FIGS. 1 to 6. The same reference symbols in the figures indicate the same structural and/or functional features.

[0043] FIG. 1 shows a fan blade 1 with a leading edge that is undulated in portions. The fan blade 1 has a leading edge 2, 4 and a trailing edge 3 and an at least partially undulated region on the leading edge, which is referred to as leading edge 4. This region of the leading edge 4 forms a wave of a specific wave form. A theoretical non-undulated leading edge of a reference blade is denoted by 2*. The leading edge has a profile that results in the shape of the leading edge without the presence of the wave. In addition, three meridional profile section lines A, B and C are drawn.

[0044] The position of the profile section A is chosen such that the chord length of the fan blade 1 with the undulated leading edge 4 corresponds approximately to the chord length of a reference blade with a non-undulated leading edge 2*. The position of the profile section B is chosen so that it runs through a wave crest of the fan blade 1 with the undulated leading edge 4. The position of the profile section C is chosen so that it runs through a trough of the undulated region (4) of the leading edge of the fan blade 1.

[0045] FIG. 2 is a detailed view of the profile section B in the undulated region of the leading edge 4 of the fan blade 1 to explain an S-shaped wave pattern. The profile with the undulated leading edge 4 leaves the reference profile with the non-undulated leading edge 2* close to the leading edge in the direction of the suction side SS and further downstream in the direction of the pressure side DS. For this purpose, the blade profile has a bulge protruding from the pressure side DS and a dent reaching in on the suction side SS (opposite the dashed reference profile).

[0046] A measure is described below as to how the waveform at the leading edge can be derived or optimized based on a sine wave. The waveform is defined by several points S of the sine curve and the course of the curve results from a spline interpolation. FIG. 3 shows a schematic view of an imaginary sine waveform 5 at the leading edge and a modified waveform 6 that runs through six support points S on the sine wave 5 and an additional support point S1 at the center of the wave. The peak-to-trough H of wave 6 is the distance from the highest point to the lowest point. The deviation from the sine wave is defined by a length h1 and the choice of the support points S. This waveform 6 provides a trough 7 of the waveform 6 that is “cut deeper” in relation to the peak-trough value H.

[0047] In comparison to the sine wave shape, the two flanks K1, K2 falling towards the trough 7 are closer together and their angle of attack is steeper in comparison to the sine wave in relation to the direction of the inflow velocity v. The effective inflow velocity, i.e. the component of the inflow velocity v perpendicular to the leading edge, with which the disturbance hits the leading edge of the fan blade, is reduced if the flanks K1, K2 are steeper. This leads to a more effective reduction of the emitted sound. Preferred values for h1 are in the range 0<h1<h with h=amplitude of the sine wave.

[0048] FIG. 4 shows a further alternative variation of the position of the support points. The support point at the center of the wave is positioned upstream against the direction of flow. Thus, an additional wave crest 8 is formed at the center of the wave. The deviation from the sine wave is defined by a length h2 and the choice of the support points S. Preferred values for h2 are in the range 0<h2<2h with h=amplitude of the sine wave.

[0049] FIG. 5 is a detailed view of the profile section C in the region of the undulated leading edge of the fan blade 1 to explain a local adjustment of the blade profile in the region of the leading edge to the inflow. The profile section is shifted in the region of the original leading edge 4 essentially perpendicularly to the center line between the pressure side and the suction side of the blade by the length h3 in the direction of the pressure side DS. The profile section adapted in this way with a modified leading edge 9 prevents flow separation and the associated noise emissions. The described advantageous adaptation of the profile section is preferably at the center of the wave. It can be both in the region of the additional wave crest 8 and in the region of the trough 7.

[0050] FIG. 6 shows an exemplary axial fan having five fan blades 1.

[0051] The implementation of the disclosure is not limited to the preferred exemplary embodiments specified above. Rather, a number of variants are conceivable that make use of the solution shown even in the case of fundamentally different designs.