Hydraulic resistance in channels with large-scale roughness: Fid-Bau Portal

Hydraulic resistance in channels with large-scale roughness

Al’tshul’, A. D. / Pulyaevskii, A. M.

Conclusions The following conclusions can be drawn from the curves presented in Fig. 2: 1. The hydraulic-friction coefficient λ for the type of roughness tested is a function of the Froude number for Fr=0.1 to 2.0. This relationship holds well for both smooth and turbulent flow conditions, the value Fr=1 not being of special significance for the curves of λ=γ(Fr). 2. Within the range Fr=0.1 to 0.3 (0.44), coefficient λ increases with a rise in the Froude number; and for Fr values in the range 0.3 (0.44) to 2.0, it diminishes. 3. For a constant value of the Froude number, a larger relative roughness Δ/h (in tests with constant roughness Δ, this corresponds to smaller depths) is characterized by higher values of coefficient λ. 4. The maximum value of curves λ=γ(Fr) is shifted to the right as the relative roughness Δ/his, reduced; from Fr=0.3 (Δ/h=0.290) to Fr=0.44 (Δ/h=0.0966). 5. The curves of λ=γ(Fr) with Δ/h constant are not symmetrical about the vertical axis: their rising, lefthand branches are steeper than their dropping, right-hand segments. 6. For Froude numbers exceeding 2.0, the effect of Fr on λ becomes less noticeable. This can be explained by the instability of the flow and the development of rolling waves, which were recorded in the tests on an oscillograph with the aid of a level gauge [T].