Inducer Design

In the design of a rocket pumps, one of the biggest drivers is making the pumps as small and thus lightweight and packagable as possible. The main issue is that a small pump inlet has a relatively high velocity and, thus, lower pressure. When the fluid then hits the impeller, the pressure drops further on the back sides of the pump blades. When this pressure drops below the vapor pressure of the pumped liquid, a gas bubble is formed and this process is known as cavitation. This is bad for the pump for two main reasons; the first is that the gas bubble formation can cause high stress and actually destroy the impeller. The second is the gas bubble, with much lower density than a liquid, blocks the flow leading to lower pressure rise and flow rate.  To get around this problem, a inducer is commonly added to the inlet of a pump impeller.

An inducer is pretty much a single stage axial pump, usually designed to pressurize the fluid to 10% of the total pump pressure and they are designed to work even with a small amount of cavitation. NASA SP-125 actually has all of the relevant design equations (sample calculation 6-7), so I won’t go over them all again in this post.

Inducer design from SP-125
Inducer design from SP-125

The basics are that you calculate a mean inducer tip speed:

Mean_Tip_Speed = sqrt ( Head_Rise * gravity / Inducer_Head_Coefficient)

with the  Inducer_Head_Coefficient being an experimental number between 0.06 and 0.15.  From the mean tip speed, you can then calculate the mean diameter and, thus, the inner and outer inducer diameter. Then you calculate the angle of attack at the the front edge using:

Flow_Angle = atan ( Inlet_Axial_Velocity / Inlet_Outer_Tip_Speed)

You then make the inlet vane angle between 1-4 degrees higher than the flow angle. You then take this tip angle and set all of the inlet angles using:

Diameter_A * tan (Angle_Of_Attack_A) = Diameter_B * tan (Angle_Of_Attack_B)

Now, for the outlet, you need to calculate the outlet flow angle using:

Outlet_Flow_Angle = atan ( Outlet_Axial_Velocity / (Mean_Outlet_Peripheral_Speed – Mean_Outlet_Tanjential_Speed))

Then you set the outlet angle equal to the Outlet flow angle + 1 degree to account for real world effects. The final thing is to choose a number of blades, usually 3-5 based on desired solidity, and you are good to go.

As you can see, I glossed over some steps, but with this and SP-125, it is actually easier to design than a impeller so good luck if you give it a go.

152 thoughts on “Inducer Design”

  2. We stumbled over here different website and thought I should check things
    out. I like what I see so now i’m following you.
    Look forward to finding out about your web page
    for a second time.

  3. It’s truly very complex in this full of activity life to
    listen news on Television, so I only use world wide web for that purpose,
    and take the hottest information.

  6. It’s in fact very difficult in this active
    life to listen news on Television, thus I simply
    use internet for that purpose, and get the hottest information.

  7. I don’t know whether it’s just me or if everybody else experiencing
    issues with your blog. It appears like some of the text on your posts are running off the
    screen. Can somebody else please provide feedback and let me know if this is happening to them as well?

    This may be a issue with my browser because
    I’ve had this happen previously. Thank you

  8. Undeniably imagine that which you stated.
    Your favorite justification seemed to be at the net the easiest factor to
    be aware of. I say to you, I definitely get annoyed
    while other people think about worries that they
    plainly do not recognise about. You managed to hit
    the nail upon the highest and outlined out the entire thing with no need side-effects ,
    people can take a signal. Will likely be back to get more.
    Thank you

  9. Thanks for the good writeup. It in truth was a entertainment account
    it. Glance complex to far added agreeable from you! By the way, how can we keep in touch?

  10. Undeniably imagine that which you stated.
    Your favorite reason appeared to be on the net the simplest factor to be mindful of.
    I say to you, I certainly get irked while other people
    think about concerns that they plainly don’t recognize about.
    You controlled to hit the nail upon the top as well as outlined out the whole thing without
    having side effect , people can take a signal.
    Will likely be back to get more. Thank you

  61. Информация от врачей и экспертов о SARS-CoV-2, на авторитетном интернет-издании Коронавирус-Контроль со ссылками на официальные и государственные источники Минздрав РФ – https://coronavirus-control.ru/vakcziny-ot-koronavirusa-v-rossii/ Эта информация для меня была ценна, добавила в закладки.

Comments are closed.