# Low-speed centrifugal compressor

## Overview of Tests

The Low-Speed Centrifugal Compressor Facility is designed to duplicate the flow fields of a high- speed subsonic centrifugal compressor in a large low-speed machine Thus the essential flow physics of the flow field can be investigated in detail. A schematic diagram of the LSCC facility is shown in figure 4. Air is drawn into the facility room through a filtered vent in the roof and then past a bank of steam pipes and louvers designed to control the air temperature to within ± 1 oF for mass flows up to 45 kg/sec. The facility room air is then drawn into the plenum through a bank of air straighteners contained between two mesh screens. Next, the air passes through a specially designed bellmouth with a 10:1 area contraction. From there it flows into the compressor and exits through a specially designed throttle valve at the entrance to the collector. The throttle valve consists of two concentric overlapping rings with holes that have been drilled in each ring and that slide relative to each other to produce a throttle. This valve design was chosen to minimize circumferential asymmetry in the static pressure distribution at the exit, such as is typically found in scroll- type collectors. The bellmouth, inlet transition piece, and shroud flow path were machined together to minimize any boundary layer disturbance that might be caused by a step in the flow path.

Figure 4.-Schematic of NASA low-speed centrifugal compressor test facility Instrumentation:

Pneumatic probes.-Spanwise probe traverses were available at stations upstream and downstream of the rotor (see figure 2). Five-hole probes with self-nulling yaw capability (figure 5) were used for all standard pneumatic probe surveys. These probes were calibrated in a steady flow duct in which the pressure and temperature could be accurately controlled. During calibration, the probe pitch angle was varied over a range of Mach numbers, and the results were used together with the five-hole probe measurements acquired in the compressor to extract total and static pressures and the pitch angle. Before a probe was installed in the compressor test rig, a check on the pitch and swirl aerodynamic zero angle was performed in a calibration jet.

Surface static pressure taps.-Static pressure taps were provided along the shroud and rotor blade surfaces. Those on the rotor surface measured the rotor blade pressure distribution and provided the opportunity for ammonia-ozalid flow visualization. They were located along quasi-orthogonal measurement planes at nominally 5, 20, 50, 80, 93, and 97 per- cent of blade span from the hub. The quasi-orthogonal measurement planes were located at approximately 2.5, 5, 15, 30, 50, 70, 90, 95, and 98 percent of meridional distance.

Laser anemometer system.- The laser anemometer system used for the present investigation was a two-component laser fringe anemometer operating in on-axis backscatter mode. Optical access to the flow field was provided by three 3-mm-thick glass windows that conformed to the flow path in both the circumferential and stream wise directions. The windows covered the inlet, knee, and exit regions of the impeller and the inlet of the vaneless diffuser. Polystyrene latex (PSL) spheres, used as seed particles, were introduced into the flow stream via four spray nozzles located in the plenum. During the development of the seeding system, an aerodynamic particle sizer was used to ensure that the seeding system could deliver mono-disperse particles and that the liquid carrier was fully evaporated by the time the seed.

Figure 5.-Schematic of five-hole pressure probes.

For Design and off-design conditions (78,7 % of design mass flow), available experimental data are listed below:

• Spanwise distribution of Pitch averaged total pressure, static pressure, total temperature, absolute flow angle, pitch angle measured from Axial at impeller exit survey station 2

• Spanwise distribution of Pitch averaged total pressure, static pressure, absolute flow angle, pitch angle measured from Axial at impeller inlet survey station 1

• Normalized shroud pitch averaged static pressure distribution

• Normalized blade static pressure distribution at 5%, 20%, 49%, 79%, 94% and 98% span from hub

• Radial velocity component, axial velocity component and relative tangential velocity normalized by tip speed at different meridional stations (From laser measurements)

• Impeller total pressure ratio

Data available only at design condition:

• Pitch angle measured from axial at 5%, 20%, 49%, 79%, 94% and 98% span from hub (From laser measurements)

Data available for a range of mass flows:

• Normalized shroud pitch averaged static pressure distribution

• Impeller total pressure ratio

The complete data are provided in the reference paper and will not all be provided for the application challenge.

The problem definition parameters (PDPs) are

• Rotation speed: 1862 rpm

• Relative flow rate

o 133-percent md (39.9 kg/s)

o 100-percent md (md=30kg/s (design condition))

o 78.7-percent md (23.6 kg/s)

NAME GNDPs PDPs (problem definition parameters) MPs (measured parameters)
Re Pr M Rotation speed (rpm) Relative flow rate Detailed data DOAPs
EXP 1 (design) ${\displaystyle 1.610^{7}}$ 0.72 0.45 1862 100% ${\displaystyle m_{d}}$ -Blade pressure -inlet spanwise distributions -pitch-averaged exit spanwise distributions -shroud pressure distribution Pressure ratio, ${\displaystyle \eta _{ad}}$
EXP 2 (off-design: low flow rate) ${\displaystyle 1.610^{7}}$ 0.72 0.45 1862 78.7% ${\displaystyle m_{d}}$ -Blade pressure -inlet spanwise distributions -pitch-averaged exit spanwise distributions -shroud pressure distribution Pressure ratio, ${\displaystyle \eta _{ad}}$
EXP 3 (off-design: heigh flow rate) ${\displaystyle 1.610^{7}}$ 0.72 0.45 1862 133% ${\displaystyle m_{d}}$ -shroud pressure distribution Pressure ratio, ${\displaystyle \eta _{ad}}$

Table EXP-A Summary description of all test cases

 Blade pressure at six different spans (5%, 20%, 49%, 79%, 94%, 98%) (PS) Blade pressure at six different span (5%, 20%, 49%, 79%, 94%, 98%) (SS) Shroud pressure distribution Inlet spanwise distribution Exit spanwise distribution DOAPs EXP 1 exp11.dat exp12.dat exp13.dat exp14.dat exp15.dat exp16.dat exp17.dat exp18.dat exp19.dat exp110.dat exp111.dat exp112.dat exp113.dat exp114.dat exp115.dat exp116.dat EXP 2 exp21.dat exp22.dat exp23.dat exp24.dat exp25.dat exp26.dat exp27.dat exp28.dat exp29.dat exp210.dat exp211.dat exp212.dat exp213.dat exp214.dat exp215.dat exp216.dat EXP 3 No Data No Data exp31.dat No Data No Data exp32.dat

Table EXP-B Summary description of all measured parameters and available datafiles

## Test Case EXP-1

Description of Experiment

For this experimental setup, the design conditions were selected. The GNDPs and the

PDPs are summarized in table EXP-A.

Boundary Data

Spanwise distribution of absolute total pressure, absolute flow angle and pitch angle are given by experiments at impeller inlet station 1 (see Figure 2).

These data are provided in the file exp114.dat

Spanwise distribution of absolute total pressure, static pressure, absolute total temperature, absolute flow angle and pitch angle are given by experiments at impeller exit station 2 (see Figure 2).

These data are provided in the file exp115.dat

No experimental data is provided for the turbulent Reynolds stresses so that assumptions have to be made for the derivation of the turbulent kinetic energy and the turbulent dissipation. The solid walls are assumed smooth.

Measurement Errors

The errors in measurement quantities for all tests are:

Aerodynamic probe measurements:

Flow angle : a = ±1.5degrees

Static and Total pressure : P,p = ± 68,95 Pa (or 0.07%)

Static temperature : T= ± 0.6 K (or 0.19%)

Mass flow rate : Mf=± 0.091 kg/s (or 0.3%)

The uncertainties are a best estimate based on precision, bias, and measurement repeatability. The Nonrepeatability is the greatest contributor to the uncertainties.

Laser anemometer measurements:

Velocity components :u,v,w=±1.5 m/s (or 2%)

The main contribution to the uncertainties comes from the window curvature. In the rear of the impeller where the window curvature and the blade span both decrease, the error is less than 2%.

Measured Data

The format of the available data files is described next

EXP1 : Experimental setup at design conditions:

exp11.dat to exp16.dat (ASCII file; headers: Blade pressure distribution on pressure side at 5%, 20%, 49%, 79%, 94% and 98% span from hub; columns: z, r, <p/pstd>)

exp17.dat to exp112.dat (ASCII file; headers: Blade pressure distribution on suction side at 5%, 20%, 49%, 79%, 94% and 98% span from hub; columns: z, r, <p/pstd>)

exp113.dat (ASCII file, headers: Shroud pressure distribution columns: z, r, <p/pstd>)

exp114.dat (ASCII file, headers: Inlet spanwise distributions :station 1 columns: r, <P/pstd>, <p/pstd>), <absolute flow angle(deg) >, <pitch angle(deg) >)

exp115.dat (ASCII file, headers: Outlet spanwise distributions :station 2 columns: z, <P/pstd>, <T/tstd>), <p/pstd>), <absolute flow angle(deg) >, <pitch angle(deg) >)

## References

Hathaway, M. D., Chriss R. M., Strazisar, A. J., and Wood, J. R., 1995, "Laser Anemometer Measurements of the Three-Dimensional Rotor Flow Field in the NASA Low-Speed Centrifugal Compressor: NASA Technical Paper, ARL-TR-333.

## Test Case EXP-2

Description of Experiment

For this experimental setup, the off-design conditions were selected (low flow rate). The GNDPs and the PDPs are summarized in table EXP-A.

Boundary Data

Spanwise distribution of absolute total pressure, static pressure, absolute flow angle and pitch angle are given by experiments at impeller inlet station 1 (see Figure 2).

These data are provided in the file exp214.dat

Spanwise distribution of absolute total pressure, static pressure, absolute total temperature, absolute flow angle and pitch angle are given by experiments at impeller exit station 2 (see Figure 2).

These data are provided in the file exp215.dat

No experimental data is provided for the turbulent Reynolds stresses so that assumptions have to be made for the derivation of the turbulent kinetic energy and the turbulent dissipation. The solid walls are assumed smooth.

Measurement Errors

The same as for EXP1

Measured Data

The format of the available data files is described next

EXP2 : Experimental setup at Off-design conditions:

exp21.dat to exp26.dat (ASCII file; headers: Blade pressure distribution on pressure side at 5%, 20%, 49%, 79%, 94% and 98% span from hub; columns: z, r, <p/pstd>)

exp27.dat to exp212.dat (ASCII file; headers: Blade pressure distribution on suction side at 5%, 20%, 49%, 79%, 94% and 98% span from hub; columns: z, r, <p/pstd>)

exp213.dat (ASCII file, headers: Shroud pressure distribution columns: z, r, <p/pstd>)

exp214.dat (ASCII file, headers: Inlet spanwise distributions :station 1 columns: r, <P/pstd>, <p/pstd>), <absolute flow angle(deg)>, <pitch angle(deg)>)

exp215.dat (ASCII file, headers: Outlet spanwise distributions :station 2 columns: z, <P/pstd>, <T/tstd>), <p/pstd>), <absolute flow angle(deg)>, <pitch angle(deg)>)

## References

Hathaway, M. D., Chriss R. M., Strazisar, A. J., and Wood, J. R., 1995, "Laser Anemometer Measurements of the Three-Dimensional Rotor Flow Field in the NASA Low-Speed Centrifugal Compressor: NASA Technical Paper, ARL-TR-333.

## Test Case EXP-3

Description of Experiment

For this experimental setup, the off-design conditions were selected (high flow rate). The GNDPs and the PDPs are summarized in table EXP-A.

Boundary Data

No experimental data is provided at boundaries

Measurement Errors

The same as for EXP1

Measured Data

The format of the available data files is described next

EXP3 : Experimental setup at Off-design conditions (high flow rate):

exp31.dat (ASCII file, headers: Shroud pressure distribution columns: z, r, <p/pstd>)

exp32.dat (ASCII file, headers: Pressure ratio and adiabatic efficiency Pressure ratio, ${\displaystyle \eta _{ad}}$

## References

Hathaway, M. D., Chriss R. M., Strazisar, A. J., and Wood, J. R., 1995, "Laser Anemometer Measurements of the Three-Dimensional Rotor Flow Field in the NASA Low-Speed Centrifugal Compressor: NASA Technical Paper, ARL-TR-333.