Partially submerged periodic riblets

1. A method for reducing drag, comprising:

forming a smooth surface on a first portion of a physical object;

forming periodic riblets on a second portion of the physical object; and

generating a flow over the periodic riblets of the second portion of the physical object and over the smooth surface of the first portion of the physical object;

wherein:

the second portion of the physical object is adjacent to the first portion of the physical object;

each peak of each riblet of the periodic riblets of the second portion of the physical object is located above a plane of the smooth surface of the first portion of the physical object;

each valley between adjacent riblets of the periodic riblets of the second portion of the physical object is located below the plane of the smooth surface of the first portion of the physical object; and

a length of each riblet of the periodic riblets runs parallel to a direction of the flow.

2. The method of claim 1 , wherein a cross sectional area in the direction of the flow of the first portion of the physical object is approximately equal to a cross sectional area of the second portion of the physical object in the direction of the flow.

3. The method of claim 1 , further comprising:

forming each peak of each riblet of the periodic riblets at a same distance above the plane of the smooth surface of the first portion of the physical object; and

forming each valley between adjacent riblets of the periodic riblets at the same distance below the plane of the smooth surface of the first portion of the physical object.

4. The method of claim 1 , further comprising:

forming each riblet of the periodic riblets at a same length; and

forming the smooth surface of the first portion of the physical object at the same length as the periodic riblets.

5. The method of claim 1 , wherein:

a maximum height of each riblet of the periodic riblets is less than 0.002 inches;

a maximum width of each riblet of the periodic riblets is less than 0.004 inches; and

a length of each riblet of the periodic riblets is within a range of 10 to 50 times longer than the maximum height of each respective riblet.

6. The method of claim 1 , wherein:

the first portion of the physical object further comprises a first transition surface;

an angle between the transition surface of the first portion of the physical object and the smooth surface of the first portion of the physical object is within a range of 90 degrees to 155 degrees;

the second portion of the physical object further comprises a second transition surface; and

an angle between the second transition surface of the second portion of the physical object and the smooth surface of the first portion of the physical object is within a range of 90 degrees to 155 degrees.

7. The method of claim 1 , wherein the physical object is associated with one of the following:

an aircraft;

a marine vessel;

a vehicle;

a pipeline;

a wind turbine; and

a projectile.

8. A physical object, comprising:

a first portion comprising a smooth surface; and

a second portion comprising periodic riblets, wherein:

the second portion of the physical object is adjacent to the first portion of the physical object;

each peak of each riblet of the periodic riblets of the second portion of the physical object is located above a plane of the smooth surface of the first portion of the physical object; and

each valley between adjacent riblets of the periodic riblets of the second portion of the physical object is located below the plane of the smooth surface of the first portion of the physical object.

9. The physical object of claim 8 , wherein a cross sectional area of the first portion of the physical object is approximately equal to a cross sectional area of the second portion of the physical object.

10. The physical object of claim 8 , wherein:

each peak of each riblet of the periodic riblets is at a same distance above the plane of the smooth surface of the first portion of the physical object; and

each valley between adjacent riblets of the periodic riblets is at the same distance below the plane of the smooth surface of the first portion of the physical object.

11. The physical object of claim 8 , wherein:

each riblet of the periodic riblets has a same length; and

the length of the periodic riblets is the same as a length of the smooth surface of the first portion of the physical object.

12. The physical object of claim 8 , wherein:

a maximum height of each riblet of the periodic riblets is less than 0.002 inches;

a maximum width of each riblet of the periodic riblets is less than 0.004 inches; and

a length of each riblet of the periodic riblets is within a range of 10 to 50 times longer than the maximum height of each respective riblet.

13. The physical object of claim 8 , wherein:

the first portion of the physical object further comprises a first transition surface;

an angle between the transition surface of the first portion of the physical object and the smooth surface of the first portion of the physical object is within a range of 90 degrees to 155 degrees;

the second portion of the physical object further comprises a second transition surface; and

an angle between the second transition surface of the second portion of the physical object and the smooth surface of the first portion of the physical object is within a range of 90 degrees to 155 degrees.

14. The physical object of claim 8 , wherein the physical object is associated with one of the following:

an aircraft;

a marine vessel;

a vehicle;

a pipeline;

a wind turbine; and

a projectile.

15. A method of manufacturing a physical object, comprising:

forming a smooth surface on a first portion of the physical object; and

forming periodic riblets on a second portion of the physical object;

wherein:

the second portion of the physical object is adjacent to the first portion of the physical object;

each peak of each riblet of the periodic riblets of the second portion of the physical object is located above a plane of the smooth surface of the first portion of the physical object; and

each valley between adjacent riblets of the periodic riblets of the second portion of the physical object is located below the plane of the smooth surface of the first portion of the physical object.

16. The method of claim 15 , wherein a cross sectional area of the first portion of the physical object is approximately equal to a cross sectional area of the second portion of the physical object.

17. The method of claim 15 , further comprising:

forming each peak of each riblet of the periodic riblets at a same distance above the plane of the smooth surface of the first portion of the physical object; and

forming each valley between adjacent riblets of the periodic riblets at the same distance below the plane of the smooth surface of the first portion of the physical object.

18. The method of claim 15 , further comprising:

forming each riblet of the periodic riblets at a same length; and

forming the smooth surface of the first portion of the physical object at the same length as the periodic riblets.

19. The method of claim 15 , wherein:

a maximum height of each riblet of the periodic riblets is less than 0.002 inches;

a maximum width of each riblet of the periodic riblets is less than 0.004 inches; and

a length of each riblet of the periodic riblets is within a range of 10 to 50 times longer than the maximum height of each respective riblet.

20. The method of claim 15 , wherein:

the first portion of the physical object further comprises a first transition surface;

an angle between the transition surface of the first portion of the physical object and the smooth surface of the first portion of the physical object is within a range of 90 degrees to 155 degrees;

the second portion of the physical object further comprises a second transition surface; and

an angle between the second transition surface of the second portion of the physical object and the smooth surface of the first portion of the physical object is within a range of 90 degrees to 155 degrees.