One, what is asthma brace up? Does centrifugal type compressor produce asthma brace up reason?
Reduce when the bear of centrifugal compressor, when capacity is less than some to be worth surely, carry of gas normally destroy, how much does aeriform eduction measure, enter suddenly go out suddenly, produce intense concussion, give out the pant noise like asthmatic patient, the instruction that can see watch of aeriform outlet pressure, flow meter right now happens substantially fluctuant, subsequently, airframe also can happen to shake acutenessly, drive export pipeline, workshop vibration, compressor will produce periodic, discontinuous growl sound. If take step not in time, compressor will produce serious destruction, this kind of phenomenon breathes heavily with respect to what be called compressor brace up, also say to fly move.
Breathe heavily brace up because Cheng hump shape causes the characteristic curve of centrifugal type compressor,be, centrifugal type compressor is its compression ratio (exit presses what P2 and entrance press P1 absolutely to compare absolutely) the relation curve between the bulk discharge with entrance gas, specific plan is as follows (among them the rotate speed that N is compressor) :
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From go up the apogee that the graph can see there is a P2/P1 below every kinds of rotate speed, this the dot says for hump, each hump dot join rises to be able to get an asthma brace up attrib border line, if place of the dotted line in the graph is shown, the shadow part with attrib border left line is not stable asthma brace up area, partial criterion runs a division for safety on the right side of attrib border line, p2/P1 of area compression ratio moves to be reduced along with the accretion of discharge Q in safety, and in asthma brace up area P2/P1 follows the accretion of discharge and increase
Hypothesis compressor works to be nodded in A below N2 rotate speed, corresponding discharge is QA, if right now a certain interference makes discharge is decreased, small, but still be inside place of safety, at this moment compression ratio can increase, namely P2 increases, can make the discharge pressure of compressor increases to restore the discharge QA when stability at this moment. But if discharge continues to drop to be less than the hump below N2 rotate speed,be worth QB, at this moment compression ratio not only won’t increase, can drop instead, namely outlet pressure P2 can drop, can appear at this moment vicious circle, the eduction quantity of compressor can continue small, p2 can continue to drop, drop to flow backwards under what gas will appear for an instant when pressure tubal a network when P2, as refluent generation, pressure tubal a network drops, fall when pressure tubal a network with compressor flow backwards when outlet pressure is equal stop, however compressor still is in locomotive condition, the gas that then compressor will pour regurgitate to come again is compressed afresh again go out, can cause P2/P1 to drop again right now, be flowed backwards to come back afresh again by the gas of extrude, this kind of phenomenon appears those who relapse, gas relapses pass in and out, generation is arranged strongly, this is so called asthma brace up.