Oscillating-flow wind tunnel studies for a circulation control circular cylinder.

Abstract

A two-dimensional circulation control (4.25 inch diameter by 24 inch span) model was designed for installation in the Naval Postgraduate School oscillating flow, low speed wind tunnel. An adjustable, tangential blowing slot was included in the design to provide a circulation control capability using the Coanda flow effect aft of the spanwise slot. Orifice locations were defined for obtaining surface static pressures which could be subsequently processed to yield section lift and drag coefficients. While the model was being fabricated, pressure system calibrations were made to determine the dynamic transfer function from a simulation of the model's static pressure orifice when connected to the pressure transducer. Similar transfer functions were determined for a static pressure probe. The existing data acquisition system was used to process the sampled digital data sequence. Clear-tunnel flow calibrations were performed in the (2 foot by 2 foot by 18.6 foot long) test section at a mid-length test station using a hot-wire and the calibrated static pressure probe. An oscillating velocity was superimposed upon a mean free stream motion using an existing rotating mechanism of four synchronized shutters at the end of the test section. Analytic estimates of both static pressure and velocity perturbations correlated well with experimental results for a frequency range of 14 to 40 Hz with a fixed value of shutter blockage. A surprising result confirmed by these test was that, although the amplitude of the velocity perturbation wave remained relatively constant at 5 percent of the mean free stream velocity, the amplitude of the static pressure wave showed a periodic dependence upon the frequency of the harmonic blockage source.