University of Manitoba
Winnipeg, Manitoba, Canada
The fully developed flow in a pipe of 10.16 cm diameter was fed into a conical diffuser at Reynolds number of 116,000. The conical diffuser had a total divergence angle of 8$\deg$, an area ratio of 4:1 and a length of 72 cm. This geometry produced dynamically an adverse pressure gradient in the diffuser. The works that are reviewed here were reported by Azad \& Hummel (1981), Arora (1978), and Arora \& Azad (1980). First, structure function and then isotropic vorticity equation will be described. All the results of structure functions show that the extent of the inertial subrange is about one decade and it is corroborated also by the spectra measurements. This behaviour is confirmed only in the core region of the diffuser flow. Next, isotropic vorticity equation was tested experimentally for its verification in the diffuser flow and was found to be only applicable in the core region of the diffuser, whose outer boundary is marked by the cylindrical surface generated by the inlet radius. Dynamically, this surface has maxima for $\overline{u^2}$, $\overline{uv}$, $\overline{uv}(\partial U / \partial y)$ and $\overline{v^2}(\partial U / \partial y)$; zero value of skewness of u, minimum value of flatness factor, less than the Gaussian value of 3 and finally at the surface, the mean velocity divided by the bulk velocity at the inlet has a value of 1/2 for all Reynolds numbers tested. Turbulent flow in the conical diffuser of the present set-up will be highly desirable for experimental verification of theories pertaining to fine scales of turbulence.
References:
[1] Arora, S. C., 1978, An Experimental Study of the Turbulent Kinetic Energy and Vorticity in a Conical Diffuser. Ph. D. Thesis, Dept. of Mech. Engrng, University of Manitoba, Winnipeg, Manitoba.
[2] Arora, S. C. \& Azad, R. S., 1980, Applicability of the Isotropic Vorticity Theory to an Adverse Pressure Gradient Flow. J. Fluid Mech. 97, 385-404.
[3] Azad, R. S. \& Hummel, R. H., 1981, Structure Functions of Turbulence in an Adverse Pressure Gradient, Phys. Fluids, 24 (10), 1774-1779.