Turbulent Flow Measurements near the Discharge Port of a Screw Compressor

Abstract

Mean flow and turbulence characteristics have been measured within the male and female rotors close to the discharge port of a double screw compressor at different radial positions, two axial positions from the exit port, H p , and two radial planes, α p. Cycle-resolved axial and tangential mean flow measurements and their corresponding turbulent velocity fluctuations were made over a time window of 1°using a laser Doppler velocimetry, LDV, system. Measurements were performed through two transparent windows near the inlet of the discharge port inside the male and female working chambers. The results revealed a highly complex 3-D flow within the male and female working chambers, in particular, near the discharge port with two distinct flow zones 1 and 2 before and after the opening of the port, respectively. The flow in zone 1 was controlled by the rotor motion while in zone 2 was greatly influenced by the discharge process. In zone 2, both components of mean velocities were subjected to a sudden increase in velocity forming strong axial and tangential jet flows due to rapid change in pressure across the port as the flow is exposed into the discharge port. It was found that the flow structures have been affected considerably by the position of the discharge port, radial planes and radial positions. Axial and tangential RMS velocity distributions within both rotors were found to be relatively high and less affected by the flow changes of zones 1 and 2 with almost uniform distribution. The measured magnitudes of axial and tangential RMS velocities suggest it would be reasonable to assume the local turbulence to be isotropic for the modelling purposes. To authors' knowledge, the results are unique, original and in great details not only to describe the flow structure, but also, they can be used in CFD codes to establish a reliable model of the flow and pressure distribution within twin screw machines.

Turbulent flow development within the discharge cavity of a screw compressor

“…Therefore a 2-D PIV system has been used to map the flow within the discharge cavity, and in order to validate the accuracy of the measured PIV data, a comparison between LDV and PIV has been made to provide confidence in the measured data. A summary of the PIV setup is given below; again, full details of both techniques have been given by current authors in Guerrato 3 and Nouri et al 16 and will not be repeated here.…”

“…The LDV and PIV techniques are well established and the systems used were the same as those used by Refs. 3,15,16,25,27 who described the LDV and PIV systems in full detail (including all related errors and uncertainties) which will not be repeated her, however, detailed summaries of both methods are provided below. The test rig was modified to accommodate the optical compressor, LDV/PIV transmitting and collecting optics, and their traverses.…”

“…A representation of convergence from W- to V-section of the port, and a schematic mean flow through the discharge port and its exposure into the cavity are also shown in Figure 3(b). In addition, another flow feature that can influence the flow through the port and also into the cavity is when the high-pressure flow from the rotor’s chamber moves into the port (at W-section) during the port opening and closing as explained by Nouri et al 16 The position of the discharge port is fixed and the opening and closing of flow is controlled by the end face of the male and female rotors and therefore the process is a gradual opening and closing depending on the angular positions of rotors. Thus, the flow exposure (or mass flow) to the port varies as θ changes, which can have considerable control on flow velocity trajectory and distribution in discharge port and cavity, see Nouri et al 16 for more details.…”

“…Previous works on the flow behaviour within screw compressors are scarce, however, there are limited experimental and CFD investigations that measured and simulated flow within the screw compressors. Full details of the flow characteristics within the suction, working chamber and near the discharge ports were measured and already reported in Nouri et al [15][16][17] by current authors. This report is the continuation of the same research project, focusing on the turbulent flow behaviours within the discharge cavity by measuring the mean and turbulence velocities using LDV and PIV techniques.…”

A Review of Recent Research and Application Progress in Screw Machines

“…However, the CFD model can provide a full 3D temperature field in the fluid and the solid parts, and it showed the rotor temperature was strongly uniform over the cross section and almost linear along the rotor axes. However, the accurate verification of the CFD model is still a technical issue, and the current verification method is limited to the flow visualization, and flow velocity field measurement in the suction and discharge port instead of the inner of the rotor chamber [81,82] or the comparison with the measured volumetric flow rate, shaft power, and p-V diagram.…”