Skin Friction Reduction Characteristics of Nonsmooth Surfaces Inspired by the Shapes of Barchan Dunes

Table 4

Orthogonal test table.

Test number	Test factors
	Depth (mm)	Angle of repose (°)	Spacing (mm)
1	(1) 4	(1) 31	(1) 25
2	(1) 4	(2) 33	(2) 30
3	(1) 4	(3) 35	(3) 35
4	(2) 7	(1) 31	(2) 30
5	(2) 7	(2) 33	(3) 35
6	(2) 7	(3) 35	(1) 25
7	(3) 9	(1) 31	(3) 35
8	(3) 9	(2) 33	(1) 25
9	(3) 9	(3) 35	(2) 30
Smooth surface	0	0	0