Do turbines cause suction ?

Replies

• 

  CE Designer

  This is a very good question, something i never thought about before.
  I hope someone can clear this up for us.
• 

  zaveri

  CE Designer

  This is a very good question, something i never thought about before.
  I hope someone can clear this up for us.

  What is your opinion on this ? what do you think of it ?
• 

  CE Designer

  #-Link-Snipped-# the material i have read thus far seem to describe flow rather than suction.
  #-Link-Snipped-#
  
  Special attention to the 5th paragraph.
• 

  Ramani Aswath

  Let us do a thought experiment. When a turbine is running let us say a cap is put on the front end. The front part of the turbine is used to compress air. If enough flow of air exists the pressure at the entrance would be near ambient. Since we have closed the end the compressor end would have removed the air . Obviously this would result in a vacuum. This is what a turbo molecular pump does to produce very high vacuum at high flows.
  PDF
  Turbomolecular Pump
• 

  zaveri

  #-Link-Snipped-# #-Link-Snipped-#
  
  thanks both of you
• 

  engg.ashish

  i didnt get it till now,😕😕
  so this means turbine creates lil bit of suction as back emf😳
• 

  zaveri

  engg.ashish

  i didnt get it till now,😕😕
  so this means turbine creates lil bit of suction as back emf😳

  yes that is what we are discussing here.
• 

  engg.ashish

  #-Link-Snipped-# so whats the result then do it create suction
• 

  zaveri

  No they dont
• 

  akpower

  Turbines which are high speed machines will definitely generate suction at inlet as the blade design of turbine pushes the working fluid to next stage.This is true even for rotary compressors.However please keep in mind that turbines are used to convert one form of energy into other and input fluid i.e. gas,steam,water, air(wind turbine)will create differential pressure across its blades.
• 

  Hammer_Time

  Actually I think the result was yes they do, but if enough airflow exists then it would only be very slight, right?
• 

  zaveri

  #-Link-Snipped-# #-Link-Snipped-#
  
  so in the end we conclude that turbines do cause suction, but is negligible, isn't it?
• 

  Hammer_Time

  That's what I'm thinking yes.
• 

  jigarmech

  according to me they dont cause any back pressure as the flow of fluid pushes the turbine to rotate so there won't be any back pressure due to a single turbine rotating but if the turbine is placed in series(say one like in jet engines) then there is a possibility of back pressure due to multiple turbine blades causing hindrance in the flow.
  
  if the flow speed reduces as compared to the turbine then it will definitely cause back pressure.
• 

  zaveri

  jigarmech

  according to me they dont cause any back pressure as the flow of fluid pushes the turbine to rotate so there won't be any back pressure due to a single turbine rotating but if the turbine is placed in series(say one like in jet engines) then there is a possibility of back pressure due to multiple turbine blades causing hindrance in the flow.
  
  if the flow speed reduces as compared to the turbine then it will definitely cause back pressure.

  can you elaborate your last sentence ?
• 

  mechky

  Suction is the flow of a fluid into a low pressure region. For suction to occur, a pressure gradient is required which propels the matter to low pressure area.
  
  There are mainly two classes of turbines that are used in power plants - Impulse & Reaction.
  In case of impulse turbine, there is no pressure gradient across the inlet and outlet of turbine so there is chance of suction to occur.
  In reaction turbines, the pressure at inlet is higher than at the outlet. So, for reaction turbines we can think that since there is a favourable pressure gradient so suction will occur.
  But whether it is true or not, it can be ensured by conducting a experiment in which inlet and outlet of turbine can be connected to a water sump and coupling the shaft of turbine to a electric motor. Connect a pressure gauge in inlet pipe and rotate the shaft with the help of motor and notice any change in pressure gauge reading.
  
  I don't think any suction will occur.
  
  This is my point of view and I may be wrong.
• 

  zaveri

  #-Link-Snipped-#
  
  what about those wind turbines ?
• 

  jigarmech

  zaveri

  can you elaborate your last sentence ?

  😨
  
  😕 lets us say the flow of fluid is flowing from left to right via turbine. Now lets assume that flow is actuated to its extreme position(i.e. valve is fully open and hence the flow is at its max.)
  This will help turbine to get going.
  Now suppose suddenly the flow is slowed down but the valve isn't closed, the turbine will take time to get proportional to flow. But till then, in mid while it is slowing down, it's still at a higher speed than the force gaining from flow. Hence at that time it will definitely create a suction pressure in the left(inlet) of turbine.
  
  hoe you got it.😉
• 

  mechky

  zaveri

  #-Link-Snipped-#
  
  what about those wind turbines ?

  No idea about that.
• 

  zaveri

  bulldozer

  in case of wind turbine,they do create suction,that too of a great magnitude.
  it seems that the birds flying there are caught in the flowing wind into these turbines which eventually die as they strike the blades of the turbines.
  the blades span 90-100m in dia rotating at very slow speeds.

  the birds which get killed in a wind turbine, i don't necessarily think get "sucked" in, but rather they may be "pushed" inside by the same wind force which acts on the blades of the turbine to rotate it.
  
  P.S : i may be wrong.