**1.2. The design and construction of a Gas Dynamics facility**

The Gas Dynamics facility consists of a large capacity compressed air plant that involved the installation in the Aerodynamics Laboratory of the University of New South Wales of a compressed air plant on the floor and the construction of an overhead structure of four iden‐ tical 200 cubic feet capacity storage pressure vessels.

The design was initiated by setting a requirement of continuous mass flow rate of about 1 lb/sec. For continuous operation, the system pressure was set to about 100 psig. The gas dy‐ namics facility was also required to provide air supply to a 3.5 inch x 4 inch supersonic wind tunnel, capable of operation of up to Mach 3.5.

A brief description of the gas dynamic facility is given next.

#### *1.2.1. Compressed air plant*

#### Compressors

From a consideration of vibration and intake resonance of the machines and also to provide significantly larger outputs per unit cost, it was decided to use rotary compressors. Two Hol‐ man RO600S screw type compressors, each rated at 600 cubic feet per minute of free air each and capable of operation separately to provide a mass flow of 0.75 lb/sec or in parallel for an output of 1.5 lb/sec were acquired. Each compressor maximum pressure ratings is 100 psig for continuous operation and 115 psig for intermittent operation such as that required for use with supersonic wind tunnels. Each unit is driven by a 150 HP 1440 RPM induction motor controlled by an auto-transformer started capable of up to 15 starts per hour. Each compres‐ sor unit was installed on 'Vulcascot' anti-vibration matting and was isolated from the dis‐ charge pipe work by means of a flexible pipe work connector. As an additional precaution, the first length of outlet pipe work to the after coolers was supported on anti-vibration matting. The result is that with both compressor operating, virtually no vibration is transmitted to the Laboratory building. A schematic of the compressed air plant is shown in Fig 1.

Control of the compressor output pressure is by either an automatic stop-start system or a con‐ stant speed uploading system operating between pre-set pressure limits. In operation, the con‐ stant speed uploading mode has been most frequently used but the original pneumatic system supplied with the compressors for this purpose proved to be unreliable. Subsequently, this was replaced with an electrical system utilising an electric control pressure gauges. This sys‐ tem has proved to be very satisfactory in operation and enables repeatable and readily varied settings of cut-in and cut-out pressure to be obtained with differentials as small as 2 psi.

The compressors are cooled by oil injection and lubricated by the same oil pressurised from a small pump. The cooling/lubricating oil is stored in a 40 gallon tank and cooled by an oil/ water heat exchanger. The air, after compression, passes through a multi-stage reverse flow oil separator with absorbent filters so as to remove most of the oil present. Claimed oil con‐ sumption is one gallon per compressor per 400 hours of operation. Fig. 3 shows the Com‐ pressor of the gas dynamics facility.

**Figure 3.** The Compressor of the Gas Dynamics Facility

In this Chapter, the design and construction of the basic gas dynamics facility (Fig. 1) is de‐ scribed first in Part I followed by that of a blow down type supersonic wind tunnel (Fig. 2) in Part II. The two facilities are currently in operation at the School of Mechanical and Man‐

The Gas Dynamics facility consists of a large capacity compressed air plant that involved the installation in the Aerodynamics Laboratory of the University of New South Wales of a compressed air plant on the floor and the construction of an overhead structure of four iden‐

The design was initiated by setting a requirement of continuous mass flow rate of about 1 lb/sec. For continuous operation, the system pressure was set to about 100 psig. The gas dy‐ namics facility was also required to provide air supply to a 3.5 inch x 4 inch supersonic wind

From a consideration of vibration and intake resonance of the machines and also to provide significantly larger outputs per unit cost, it was decided to use rotary compressors. Two Hol‐ man RO600S screw type compressors, each rated at 600 cubic feet per minute of free air each

ufacturing Engineering of the University of New South Wale.

76 Wind Tunnel Designs and Their Diverse Engineering Applications

**Figure 2.** A side view of the 5 ½ inch x 4 inch Supersonic Wind Tunnel

tical 200 cubic feet capacity storage pressure vessels.

A brief description of the gas dynamic facility is given next.

tunnel, capable of operation of up to Mach 3.5.

*1.2.1. Compressed air plant*

Compressors

**1.2. The design and construction of a Gas Dynamics facility**
