# Strategically Preparing Fluid Mechanics for GATE Mechanical

Fluid mechanics and its applications is one of the core subjects for mechanical engineering. So, obviously it carries a decent weightage in GATE. It is a vast subject and syllabus of GATE covers a part of that. Also, being one of the core subjects, it is the kind of subject that helps you understand other subjects like turbo machinery, Heat and mass transfer etc. Many people are confused how to go about studying FM for GATE. In this blog, I will be telling you exactly that, along with some key points and tips.

**Last 10 years marks weightage for FM/FMC in GATE – Mechanical :-**

Year | 2017 | 2016 | 2015 | 2014 | 2013 | 2012 | 2011 | 2010 | 2009 | 2008 |

Marks* | 7 | 11 | 9 | 8 | 6 | 5 | 3 | 6 | 8 | 7 |

** **

*****Marks are taken as average wherever multiple sets are involved.

From the above distribution, it is evident that FM carries good enough weightage. Average marks that comes in GATE paper is between 7 to 8. The toughness of the question differs from year to year but it is generally seen that there are good conceptual questions from this subject.

**Books/notes required* –**

- Mechanical GATE Krash notes by Kreatryx – For basic preparation and understanding the concepts.
- “Introduction to Fluid Mechanics” – Som and Biswas – For referring some of the concepts and solving basic numerical.
- “Fluid Mechanics and Hydraulic Machines: Problems and Solutions” – by Subramanya – For solving/practicing numericals.
- NPTEL lectures by Prof Som. – For referring any doubts for particular topics.

*These are the books recommended by me but if you are comfortable with any other standard books, then choose it. I would highly recommend book by Subramanya for practice in place of any other as it covers all kind of numericals.

**Syllabus – **

I will be dealing with the syllabus in detail but the rough cut of the syllabus is as below –

Fluid Properties , Fluid Statics, Manometry, Buoyancy, Forces on Submerged Bodies, Stability of Floating Bodies , Control-Volume Analysis of Mass, Momentum and Energy , Fluid Acceleration , Differential Equations of Continuity and Momentum , Bernoulli’s Equation , Dimensional Analysis , Viscous Flow of Incompressible Fluids , Boundary Layer , Elementary Turbulent Flow , Flow Through Pipes, Head Losses in Pipes, Bends and Fittings. Turbomachinery, Impulse and Reaction Principles, Velocity Diagrams, Pelton-Wheel, Francis and Kaplan Turbines

I have included Application part as well because it is better to complete that part of the syllabus of GATE along with the basic Fluid Mechanics syllabus.

**Time required for whole subject – **20 days (Without counting any breaks)

**How to study?**

Now that you have everything, you should be ready to start. You should have basic knowledge of this subject since it is taught in detail during any engineering course as well. Before starting, just make sure to have your notes ready with you along with Som and Biswas and Subramanya or any other book that you have decided to refer. I would recommend keeping a separate notebook to make notes. Make note of anything that you understood or would like to refer later on. Also, in the same note, write down all the formulas topic wise.

Note – For the sub-topics which are in ** Bold and italic**, solve as many numerical as possible.

**Flow and fluid properties –**

**Topics covered – **Relationship between stress and strain for Newtonian fluids, viscosity, incompressible and compressible flows, ** manometry, Hydrostatics: Buoyancy, forces on submerged bodies, stability of floating bodies, **differences between laminar and turbulent flow.

**How to study – **Refer the notes for the theory part. Manometry part is very easy to solve once you understand the concept. There is always atleast one question from this topic, so make sure you understand the concept. It is very important to understand the concept of hydrostatics to solve problems of buoyancy, forces on submerged bodies and stability of floating bodies. All these topics are inter-related. Wherever there is doubt in concept, I would recommend referring the book and if doubt persists, then refer NPTEL for that topic only.

**Numericals** – Solve 50 % of solved numerical from Subramanya. Try and solve some of the 3 star problems from unsolved ones.

**Time required** – 3 days.

**Fluid Kinematics –**

**Topics covered – **Concept of local and convective accelerations, Eulerian and Lagrangian description of fluids motion, steady and unsteady flow.

**How to study –** These topics are more mathematical related and numerical are very easy to understand. Refer them only from notes and you will be done. There are some important theory parts as well like understanding steady and unsteady flow for which you can refer notes or book.

**Numericals** – Solve 30 % of solved numerical from Subramanya.

**Time required** – 1 day.

**Integral analysis –**

**Topics covered – Control volume analysis for mass, momentum & analysis.**

**How to study –** It is very easy topic to cover. There is no need to refer book also. Just study it through the notes and solve some numericals and you are done with this topic.

**Numericals** – Solve 30 % of solved numerical from Subramanya.

**Time required** – 1 day.

**Differential Analysis –**

**Topics covered – **Concept of fluid rotation, *Differential equations of mass and momentum for incompressible flows: inviscid – Euler equations and viscous flows – Navier-Stokes equations, vorticity, exact solutions of Navier – Stokes equation for Couette flow and Poiseuille flow, stream functions and potential functions*

**How to study – **This basically covers a part of fluid dynamics. Majority of the questions from these topics are formula based. So, it is very important to remember all the formulas. Some of the questions from vorticity are conceptual. So, it is important to understand the working for this part. The numerical questions from stream functions and potential functions are very easy and formula based. Try and cover all these topics from notes itself. If any doubt in the concept or formula, you can refer the book.

**Numericals** – Solve 50 % of solved numerical from Subramanya. Try and solve some of the 3 star problems from unsolved ones.

**Time required** – 3 days.

**Inviscid flow –**

**Topics covered – Bernoulli’s equation – assumption and application**, source, elementary plane flows, sink and doublet and their superposition for potential flow past simple geometries.

**How to study – **Bernoulli’s equation is mother of all equations. There will definitely be atleast one question where you have to apply this equation. So, it is important to understand where and how to use this equation. Other topics are not so important and mostly theory part or application of Bernoulli’s equation.

**Numericals** – Solve 60 % of solved numerical from Subramanya involving Bernoullis’s equation. Try and solve some of the 3 star problems from unsolved ones.

**Time required** – 2 days.

**Dimensional analysis –**

**Topics covered – Kinematic and dynamic similarity**, Concept of geometric, some common non-dimensional parameters and their physical significance Froude number and Mach number, Reynolds number.

**How to study – **Although the topic is very simple, it is advisable to go through the theory part through the book once. Normally in GATE, numericals are asked based on the given similarity for which various formulas are there. So, remember all the similarity formulas. Mostly, these numericals can be solved just by applying formulas. Also, remember all different kind of numbers as they may be useful in solving some of the numericals.

**Numericals** – Solve 50 % of solved numerical from Subramanya. Try and solve some of the 3 star problems from unsolved ones.

**Time required** – 2 days.

**Internal flows –**

**Topics covered – Empirical relations for laminar and turbulent flows; friction factor & Darcy Weisbach equation, fully developed pipe flow, losses in pipe flow.**

**How to study – **The topic is small but covers huge variety of numericals. You will have to remember the basic empirical relations for laminar flows for solving some of the numericals. Generally for turbulent flow, there is no need for remembering the empirical relations. Friction factor and DW relation are both very important. There are also wide ranges of numericals from pipe flows which are mostly formula based. Since, the whole topics is formula based, you will have to remember all the formulas without fail.

**Numericals** – Solve 60 % of solved numerical from Subramanya. Try and solve some of the 3 star problems from unsolved ones.

**Time required** – 3 days.

**Prandtl boundary layer equations –**

**Topics covered – Qualitative idea of boundary layer and separation, drag and lift forces**, Concept and assumptions, streamlined and bluff bodies,

*Flow measurements: Pitot – static tube and orifice plate, Basic idea of flow measurement by venturimeter.***How to study – **There will be several empirical relations here as well which you need not remember. But it is important to understand the concept of boundary layer. If you are having difficulty, I would recommend watching the NPTEL lecture by Prof Som on boundary layers. There are some simple numerical in drag and lift forces. This topic has some theory part as well which you can go through the notes and/or book. I would also recommend understanding the concept of all flow measurement devices instead of remembering their formulas as it will help you solve numerical better.

**Numericals** – Solve 50 % of solved numerical from Subramanya. Try and solve some of the 3 star problems from unsolved ones.

**Time required** – 2 days.

**Applications –**

**Topics covered – Impulse and Reaction Principles, Velocity Diagrams, Pelton-Wheel, Francis and Kaplan Turbines**

**How to study – **The application part is also one of the most important. There are some of theory parts for different types of turbines which you can go through notes/book. Understanding velocity diagram is very important. If you have any doubt at all, go through the NPTEL videos by Prof Som on velocity diagrams. There will be some basic numerical which can be solved easily once you understand the velocity diagrams

**Numericals** – Solve 40 % of solved numerical from Subramanya. Try and solve some of the 3 star problems from unsolved ones.

**Time required** – 2 days.

**Point to remember while preparing –**

- Although I have mentioned the time frame for all the topics, take little more time if you feel like you are not able to solve the numericals. Move on to the next topic only when you are satisfied with previous topic.
- Since FM is one of subjects which is mostly about numericals, solve as many numericals as possible. I have given an idea of how many numericals to be solved from each topic but it is always better to solve more. I would recommend solving numericals as I suggested and then while revising, you can always solve more.
- Notes are necessary to understand the concept. Normally on your first time preparation of subject, refer both notes and book for theory part. Move to NPTEL only if you have doubt. While revising, only refer the notes and the separate notebook which you have prepared.
- Once you are done with the subject, solve last 15 year papers. IF you are able to solve 75% or more numericals, you are in right track.
- You have to remember all the formulas. So, in your separate notebook, keep all the formulas ready and refer them for 10 to 15 minutes every night before sleeping so that you don’t forget them.
- Do not spend more than 25 days for the whole subject.
- Give mock tests as soon as you are done with the topic/subject.

If you do this much, it will be more than sufficient for preparation of FM.

Good luck!

Rishabh Bhaduria (AIR 130 in GATE 2015)

BPCL