ignore that dislike sir. I am quite certain that the guy hasn't seen this lecture.I have seen and taken a lot of lectures both offline and online and i can bet,there is no faculty out there who can explain these concepts with such ease.🙏🙏🙏🙏 glad you are on RU-vid.
Very many thanks. This is so much more helpful than I've found before (because I was never sure what Vr was relative "to") I think it better to say "B1 is angle between rel. vel and the circumferential velocity, U1". Also it takes a moment to see that V1 is where it is: but the key is always U1: Vr1 is determined as its cosine and V1 as a sin. Presumably this gives a 90 deg position. At 40 min 20 sec, the rel vel is what person the blade sees, namely the water shooting out but being left behind. I still can't get my head around Vf2 - which is a function of exit blade angle and outer diameter - **being equal to V1**. I do understand how "Whirl velocity" arrives as the vector value parallel to U2, because along with Vf2, it equals Absolute velocity, itself determined by U2 and Vr2.
Esteemed Sir, You have kindly answered some of my questions. I now wish to make a remark: the analysis, historically, came from Turbine design, for "water wheels," when the one thing known, was Flow. So that becomes a starting point in these examples. But **why should we know Flow in advance** for a pump? I think the analysis can be done without this. You would think that a blade cutting water at a certain velocity would have a predicable flow along its surface, as long as rather small angles (eg 10 - 40 deg) were used. It would mean that at Inlet, Rel Velocity would immediately be known and so Radial velocity could be calculated. All else follows. I cannot see any fallacy here-in. [Imagine the blade cutting the water, the water's movement along the blade will be the same as the tangential velocity of the Inlet circle.]
Thank you, I am quite shocked to see that someone put dislike. It was not expected really after putting this much of effort. Well it's okk., I will look forward for further improvement. But I am quite hopeful that if someone watches the video with patience, definitely he or she will understand how to draw velocity triangle.
Thankyou dear learner for your love and support. I am overwhelmed. However right now I don't need any donation. Don't take it in a negative manner. You are a beautiful soul!
U is "given" and Vr is line of blade angle. Draw V normal to U first and *then* show you *always* have a parallelogram. Also, rel velocity *must* be > tangential (=rotational) vel, because it is rotational vel + a radial component.
Many thanks for the approval. I still have not got my head around the Two superimposed vectors. I think they are being multiplied, not added; Vw2 and U2. I guess I don't quite know what Vw2 actually means.
I am still stuck at the outlet! The rel vel (Vr2) is a combination of "you" travelling around, Below the horizon, viewing the water apparently rising outward. So it must be > U2. But if you draw it as such, V2 becomes *same* as a radial flow. But you emphasise otherwise.
Dear if you are getting confused from my lecture. You can see other lectures as well or you can study from a standard textbook also. However in the video whatever I had taught is absolutely correct.
Vr2 will be in the direction of the blade line at outlet. U2 will be much greater than U1 . Then complete the vector diagram by joining V2 as the resultant. You will see a large Vw2 component . And that is what is desirable in case of pump. Then that Vw2 (velocity head) needs to be converted to pressure head which is been done in the blade passages and in the scroll casing. That's it dear. It is easy .
@@RohitChowdhury_sajaysaini Thank you again. I have looked at books also & I am sure you are right. But, concerning rel vel, I still imagine that it must be greater than U2 because it is "being left behind circumferentially but also moving in some radial direction". So it should always > U2. Perhaps I should ask: when you drew Vr2, how did you know its length? Sorry to be a bother.
Whatever I have drawn is not upto the scale. It's just a representation to help you find the magnitudes of different velocities. I can give you one suggestion. Take one numerical problem. Draw a velocity triangle representation. Then find out the values. You will get to know that which one will be larger.
When you explain the direction of the flow with the water entering hte impaler axially but the vane purely radially, you could maybe reccomend people check out this animation if they dont understand it ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-BaEHVpKc-1Q.html, this video has a very nice diagram where they show what you explained there.
