[Q&A] 2017.6.30

Surge is a type of abnormal vibration that occurs in turbine compressors when the flow rate decreases to a certain level

When the inlet flow rate to the compressor becomes low enough, severe rotational stall occurs throughout the diffuser flow channel. The outlet pressure of the compressor drops suddenly, causing the pressure in the pipeline network to be higher than the compressor’s outlet pressure; this forces the airflow to flow back into the compressor. Once the pressure in the pipeline network drops below the compressor’s outlet pressure, the compressor resumes supplying air to the network and returns to normal operation. When the pipeline pressure returns to its original level, the flow rate remains below the surge flow rate of the unit; the compressor experiences rotational stall again, the outlet pressure drops, and the airflow in the pipeline flows back into the compressor. This process repeats over and over: at times, air flow is directed into the pipeline network, and at other times it flows back to the compressor, causing significant fluctuations in the compressor’s flow rate and outlet pressure. These fluctuations result in intense air flow variations within the compressor, and this phenomenon is known as compressor surge.

When a centrifugal compressor operates at low flow rates, vortices are generated within the flow channels of the impeller and diffuser. The formation and disappearance of these vortices cause intermittent blockages and openings in the fluid flow channels, leading to periodic vibrations in the airflow and blades. This results in severe periodic vibrations and roaring noises within the compressor; this phenomenon is known as \"surge\" in centrifugal compressors.

When the inlet flow rate to the compressor becomes low enough, severe rotational stall occurs throughout the diffuser flow channel. The outlet pressure of the compressor drops suddenly, causing the pressure in the pipeline network to be higher than the compressor’s outlet pressure; this forces the airflow to flow back into the compressor. Once the pressure in the pipeline network drops below the compressor’s outlet pressure, the compressor resumes supplying air to the network and returns to normal operation. When the pipeline pressure returns to its original level, the flow rate remains below the surge flow rate of the unit; the compressor experiences rotational stall again, the outlet pressure drops, and the airflow in the pipeline flows back into the compressor. This process repeats over and over: at times, air flow is directed into the pipeline network, and at other times it flows back to the compressor, causing significant fluctuations in the compressor’s flow rate and outlet pressure. These fluctuations result in intense air flow variations within the compressor, and this phenomenon is known as compressor surge. Generally, the larger the capacity of the pipeline network, the greater the surge amplitude and the lower the frequency; conversely, the smaller the capacity of the pipeline network, the smaller the surge amplitude and the higher the frequency.

Due to insufficient flow rate, the compressor experiences severely low outlet pressure and may even experience backflow, which leads to vibrations.

The periodic oscillations of the fluid in fluid machinery and its pipelines are mechanical vibrations that occur as a result of the fluid being periodically drawn in and discharged. For example, the surge phenomenon that can occur during the operation of a pump or compressor is as follows: when the flow rate drops to its minimum value, the outlet pressure suddenly falls, and the pressure in the downstream pipeline becomes higher than the outlet pressure. As a result, the medium being transported flows back into the machine, until the outlet pressure rises again and the medium is sent forward once more through the pipeline ； When the pressure in the pipeline returns to its original level, the flow rate decreases again, and backflow of the medium in the pipeline occurs, repeating this cycle over and over.

When the compressor operates in conjunction with a piping network of a certain volume, and at high compression ratios and low flow rates, once the flow rate falls below a certain threshold, the airflow on the back side of the blades becomes severely disengaged, leading to blockages in the passages. This results in intense fluctuations in the airflow, and oscillations occur between the gas volume and resistance in the outlet piping network. At such times, the parameters of the airflow in the compressor and piping system experience significant fluctuations over time, with both the gas volume and pressure changing periodically on a large scale； Both the power and noise level of the compressor vary periodically. The aforementioned changes are extremely intense, causing the machine body to vibrate violently to the point where it cannot operate properly. This phenomenon is called surge. Since surge is a phenomenon that occurs in the entire piping system, it is related not only to the flow characteristics inside the compressor but also depends on the properties of the piping system; its amplitude and frequency are determined by the volume of the piping system.

During operation, as the flow rate of the compressor continues to decrease and reaches its minimum value, severe rotational separation occurs within the compressor’s flow channels, causing the outlet pressure to drop suddenly. When the outlet pressure of the compressor drops, the pressure in the pipeline network does not decrease; as a result, the gas in the pipeline network flows back into the compressor. When the pressure in the pipeline network drops below the pressure at the compressor outlet, the backflow stops and the compressor begins to supply air to the pipeline network again, returning to normal operation. However, once the pressure in the pipeline network rises back to its original level, the compressor’s flow rate decreases again, causing gas to flow back in the system. This process repeats over and over, resulting in periodic fluctuations in air flow within the entire system, a phenomenon known as surge.

During operation, as the flow rate of the compressor continues to decrease and reaches its minimum value, severe rotational separation occurs within the compressor’s flow channels, causing the outlet pressure to drop suddenly. When the outlet pressure of the compressor drops, the pressure in the pipeline network does not decrease; as a result, the gas in the pipeline network flows back into the compressor. When the pressure in the pipeline network drops below the pressure at the compressor outlet, the backflow stops and the compressor begins to supply air to the pipeline network again, returning to normal operation. However, once the pressure in the pipeline network rises back to its original level, the compressor’s flow rate decreases again, causing gas to flow back in the system. This process repeats over and over, resulting in periodic fluctuations in air flow within the entire system, a phenomenon known as surge.