Skewed axial fan assembly
A free-tipped axial fan assembly has a skew distribution which reduces fan noise while minimizing radial tip deflection. The difference between the maximum value of leading-edge skew and the value of leading-edge skew at the fan radius is at least 10 degrees. The ratio of the difference of the leading-edge skew between the maximum value and the value at the fan radius to the difference of the trailing-edge skew between the maximum value and the value at the fan radius is at least 2.5.
1. A free-tipped axial fan assembly comprising:
a fan rotatable about an axis and having a radius R and a diameter D, the fan comprising a hub, the hub having a radius R hub , and a plurality of blades extending generally radially from the hub, each of the plurality of blades having a leading edge, a trailing edge, a blade tip, and a span S equal to the difference between the fan radius R and the hub radius R hub ; and
a shroud comprising a shroud barrel surrounding at least a portion of each of the plurality of blade tips, a tip gap being defined between the shroud barrel and the blade tips,
wherein each of the plurality of blades has a geometry, as viewed in axial projection, which at every radial position has a leading-edge skew angle and a trailing-edge skew angle, the leading-edge skew angle having a maximum value, and the difference between the maximum value of the leading-edge skew angle and the leading-edge skew angle at the fan radius R being at least 10 degrees,
wherein the trailing-edge skew angle has a maximum value, and the difference between the maximum value of the leading-edge skew angle and the leading-edge skew angle at the fan radius R is at least 2.5 times the difference between the maximum value of the trailing-edge skew angle and the trailing-edge skew angle at the fan radius R, and
wherein the fan radius R is measured at the trailing edge in the case of a fan with flared blade tips, and in the case of a locally-rounded blade tip at the trailing edge, is measured at the point where the tip gap is at a substantially minimum value.
2. The free-tipped axial fan assembly of claim 1 , wherein the difference between the maximum value of the leading-edge skew angle and the leading-edge skew angle at the fan radius R is at least 3.5 times the difference between the maximum value of the trailing-edge skew angle and the trailing-edge skew angle at the fan radius R.
3. The free-tipped axial fan assembly of claim 1 , wherein the difference between the maximum value of the leading-edge skew angle and the leading-edge skew angle at the fan radius R is at least 4.5 times the difference between the maximum value of the trailing-edge skew angle and the trailing-edge skew angle at the fan radius R.
4. The free-tipped axial fan assembly of claim 1 , wherein the difference between the maximum value of the leading-edge skew angle and the leading-edge skew angle at the fan radius R is at least 15 degrees.
5. The free-tipped axial fan assembly of claim 1 , wherein the difference between the maximum value of the leading-edge skew angle and the leading-edge skew angle at the fan radius R is at least 20 degrees.
6. The free-tipped axial fan assembly of claim 1 , wherein the maximum value of the leading-edge skew angle is at least 2 degrees.
7. The free-tipped axial fan assembly of claim 1 , wherein the maximum value of the leading-edge skew angle is at least 5 degrees.
8. The free-tipped axial fan assembly of claim 1 , wherein the maximum value of the leading-edge skew angle is at least 9 degrees.
9. The free-tipped axial fan assembly of claim 1 , wherein the maximum value of the leading-edge skew angle occurs at a blade spanwise position that is between about 0.2 times the blade span S and about 0.6 times the blade span S.
10. The free-tipped axial fan assembly of claim 1 , wherein the maximum value of the leading-edge skew angle occurs at a blade spanwise position that is between 0.3 times the blade span S and about 0.5 times the blade span S.
11. The free-tipped axial fan assembly of claim 1 , wherein the shroud barrel is flared, and the blade tip leading edge extends further radially outward than the blade tip trailing edge.
12. The free-tipped axial fan assembly of claim 1 , wherein the tip gap is less than 0.02 times the fan diameter D.
13. The free-tipped axial fan assembly of claim 1 , wherein the plurality of blades are molded of a plastic material.
14. The free-tipped axial fan assembly of claim 1 , wherein the fan assembly is a puller-type automotive engine-cooling fan assembly.
15. The free-tipped axial fan assembly of claim 1 , wherein each of the plurality of blades has a geometry, as viewed in axial projection, which at every radial position has a leading-edge sweep angle, and the leading-edge sweep angle at the fan radius R is at least 47 degrees in a backward direction.
16. The free-tipped axial fan assembly of claim 1 , wherein each of the plurality of blades has a geometry, as viewed in axial projection, which at every radial position has a leading-edge sweep angle, and the leading-edge sweep angle at the fan radius R is at least 55 degrees in a backward direction.
17. The free-tipped axial fan assembly of claim 1 , wherein each of the plurality of blades has a geometry, as viewed in axial projection, which at every radial position has a leading-edge sweep angle, and the leading-edge sweep angle at the fan radius R is at least 62 degrees in a backward direction.