Open-Circuit Wide-Angle Low-Speed Blower Wind Tunnel for Propellers Testing

Aeronautical and Space-Rocket Engineering


Аuthors

Karpovich E. A.*, Zanegin S. Y.**

Moscow Aviation Institute (National Research University), 4, Volokolamskoe shosse, Moscow, А-80, GSP-3, 125993, Russia

*e-mail: karpovichea@mai.ru
**e-mail: zaneginsy@mai.ru

Abstract

This article presents the design, analytical and numerical analysis, as well as key specifications of a compact, open-circuit blower-type wind tunnel, developed for the propellers with the diameters up to 20 inches (0.508 m) dynamic testing under the forward speed of 20 m/s. The primary design objective consisted in achieving a uniform low-turbulent flow in the working section within the stringent spatial and budgetary constraints with the already existing centrifugal blower. The project employs the VTS 14-46-6.3 centrifugal blower equipped with the electric motor of 15 kW with the rated engine speed of 960 rpm. The blower ensures maximum air-flow rate of 20 500 m3/hour and total pressure of 1 790 Pa.
The following configuration for the wind tunnel was selected based on literature analysis: the diffuser with the 30° opening angle follows the blower outlet; settling chamber, a contraction section, and finally the working section are placed behind the diffuser. To simplify manufacturing, the entire wind tunnel is of square cross-section.
Two screens in the diffuser, one screen (honeycomb) and two grids in the settling chamber are installed for the flow control inside the channel.
Application of the diffuser with wide opening angle, as well as a square cross-section is a trade-off decision that prioritizes compactness and manufacturability, which, however, inherently creates a risk of the flow separation and a higher level turbulence in the working section. To optimize the wind tunnel characteristics, a parametric CDF-study, in which the effect of the length of straight section, which couples the blower and diffuser, and the presence of porous media (screens and honeycomb) on the flow quality key indicators was conducted.
The computations indicate that the increase of the straight section length and wire meshes and grid installing enhance significantly the flow uniformity in the working section. The optimized configuration with the straight section length of 900 mm allowed achieving the flow uniformity increase in the working section by 165%, and average turbulence intensity reduction to 1.13%, i.e. by 61%; the flow misalignment reduction by 16%, and average velocity increase in the working section by 13% compared to the basic prototype. Analytically evaluated maximum flow velocity in the working section with the 0.81  0.81 m cross-section is 14.7 m/s. The wind tunnel structure is being built from 6mm plywood with external strengthening ribs. Its settling chamber is modular and consists of several box-like elements. These elements sizes variation allows changing the distance between the meshes. The whole section with honeycomb can be replaced if necessary. The honeycomb cells are planned for production via 3D-printing (FDM/SLA). The authors suggest dividing cross-section of the entire structure into the sections aliquot to the printing area of the corresponding printer (290 × 290 mm for the FDM, and 290  160 mm for the SLA)


Keywords:

open-circuit wind tunnel, wide-angle diffuser, propeller dynamic testing, working section flow quality, outlet straightener

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