Centrifugal Compressor Stage Performance Test Rig
Single-stage test rig operating with traverse and particle image velocimetry systems
Rapid-prototyped inlet guide vane assemblies (above) and volute (below)
SwRI operates a compressor performance test rig for fast-turnaround development testing of various centrifugal compressor stage configurations. This work is performed in a Single Stage Test Rig (SSTR), which consists of a 200 hp (150 kW) electric motor with variable speed drive, a speed-increasing gearbox (11:1 ratio), and a high-speed spindle rotor assembly that can operate up to 40,000 rpm. The rig is easily configurable for detailed internal measurements, including total and static pressures and temperatures, dynamic pressures, flow angles, and traverse systems. Inlet and exit piping measurement locations are configured such that they satisfy distance requirements for ASME PTC-10 for compressor performance and ASME PTC-19.5 for flow measurement. All instruments are calibrated (NIST-traceable) to minimize uncertainty in performance measurements.
Single Stage Test Rig Design Enables Fast-Turnaround
Single stage test rig layout, simple collector configuration
In the SSTR, the impeller is mounted to the spindle rotor assembly with a precision pilot fit and a tie bolt, which allows the impellers to be installed and removed without disassembly of the rotor shaft, bearings, seals, and coupling, greatly simplifying configuration changes for efficient turnaround times between tests. The rotating and stationary assemblies are mounted on centerline risers which maintain alignment even for dissimilar thermal growths in the test and drive sections. Flow rate is typically measured at the inlet to the SSTR using a calibrated bellmouth Venturi, and throttling takes place at the discharge via a control valve, although different throttling and metering configurations are possible depending on customer requirements. The SSTR housing is insulated to minimize heat transfer to the environment. A representative layout is shown in the image above.
The rig accommodates various impeller geometries by manufacturing of custom shroud side (and hub side, if necessary) diffuser pieces. Custom seal inserts (both hub and eye seals) and transition pieces are also manufactured for each impeller. In this manner, various seal configurations can be tested. The diffuser gap and alignment can be set on both sides via axial and angular adjustment of the stator plate (hub side) and shimming of the shroud side diffuser piece against the front cover plate. The rig is also ideal for testing various inlet guide vane, diffuser, volute and/or return channel geometries economically due to its ease of access and low pressure design. Past work has leveraged rapid prototyping technologies for fast and cost-effective implementation of various geometry configurations, including direct metal laser sintering for impeller fabrication, selective laser sintering with high-temperature materials for inlet guide vane assemblies, and 3D-printed sand casting molds for volutes.