Compressor deep surges are observed to be of either near-resonant type or convective type. The differences of the behaviors and the boundaries between both types were tried to make clear in the situations of a single-stage axial compressor on the basis of numerical-experimental results by use of a surge simulation code. In the near-resonant surges, the surge frequencies relative to the resonance frequency range roughly from 0.9 to 1.1, close to the resonance condition. The surges tend to degenerate just above or in the resonance range. The convective type is said to perform actions of emptying and filling the flow in the delivery plenum, showing lower relative surge frequencies less than 0.9. The study for the criteria governing the boundary between both surge types has suggested an axial motion parameter as the candidate. The convective surges are observed to occur above the boundary value of the axial motion parameter. In the environment, the fluctuation amplitudes tend to be larger than those in the near-resonant surges. The situations force the compressor to work over a wider range from the turbine-action zone to the deeply-reverse flow zone along the stage characteristic. The flow reversals thus reinforced will enhance the so-called emptying and filling actions in the convective surges.

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Drilling sampling technology is an important means for obtaining underground physical data and evaluating mineral reserves. The coring diamond bit is located in the front of the drilling equipment, which can reflect the drilling efficiency and core recovery of the bit when drilling into the coring. In order to improve the drilling efficiency and core recovery, a design scheme of diamond bit for seafloor drills is proposed, which combines the formation characteristics of the seafloor within 300 meters. Based on the fluid dynamics theory and considering the effect of bit rotation on the flow field at the hole-bottom, the effects of bit water passage structure and drilling parameters on the flow field are analyzed. The results show that the designed bit can avoid the core erosion by 80% of the drilling fluid. The rotary speed should be controlled at 250 - 330 rpm, and the pump displacement should be 50 - 60 L/min. When the drilling fluid is up-return along the hole wall, the velocity first rises and then drops, then stabilizes between 0.8 - 1.3 m/s, which meets the range requirements for the standard cuttings up-return and the stability of the hole wall. Finally, the rationality of the bit design scheme is verified by field drilling experiments. The average core recovery percent reaches 85 %, which is about 25% higher than the conventional bit of water passage system.

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High-pressure-ratio multi-stage axial flow compressors tend to show complicated behaviors of frequencies in deep surges, including discontinuous changes. The phenomena for a nine-stage compressor were investigated by one-dimensional numerical simulations. The phenomena were found to occur somewhere in the range of roughly (90 – 100)% of the design speed, where incomplete surge recoveries, i.e., premature surge recoveries accompanied by immediate re-stallings, tend to occur, resulting in longer surge periods and lower surge frequencies. The incomplete surge recoveries are found to occur by premature unstalling owing to re-ingestions of the reversed hot air produced by the preceding surge, which is too hot for the compressor to work normally. The re-ingestion temperature, and the duration time of the hot re-ingestion relative to the normal suction appear to affect significantly the recovery process. It tends to occur essentially in the range of (90 -100)% of the design speed, where the compressor working conditions are changeable sensitively to small changes in the working conditions. The situations are found to be governed mainly by the following parameters; the representative tip Mach number, the reduced resonance frequency related with the suction flowpath, and the relative location of the compressor in the whole flowpath. Sufficiently below and above the sensitive speed range, the situations keep their respective stable and continuous surge behaviors. In the higher speed range, the deep surges having lowered frequencies at higher speeds become the normal state. The phenomena depend strongly on the design conditions, i.e., speed and pressure ratio and number of stages. The above conclusions suggest the natures of the discontinuous frequency behaviors in high-pressure-ratio multi-stage compressors, although they are qualitative in that they are strongly influenced by the present particular design conditions and the accuracies of the employed analysis.

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