Rocket Physics The Rocket Nozzle

Slides:



Advertisements
Similar presentations
Chapter Seven Compressible Fluid.
Advertisements

Example 3.4 A converging-diverging nozzle (Fig. 3.7a) has a throat area of m2 and an exit area m2 . Air stagnation conditions are Compute.
Marat Kulakhmetov.  AS8 AS8.
Analysis of Rocket Propulsion
Chapter 17 Compressible Flow Study Guide in PowerPoint to accompany Thermodynamics: An Engineering Approach, 5th edition by Yunus A. Çengel and.
Gas Turbine Cycles for Aircraft Propulsion
Lecture #12 Ehsan Roohi Sharif University of Technology Aerospace Engineering Department 1.
Isentropic Flow In A Converging Nozzle. M can equal 1 only where dA = 0 Can one find M > 1 upstream of exit? x = 0 Converging Nozzle M = 0.
Chap 5 Quasi-One- Dimensional Flow. 5.1 Introduction Good approximation for practicing gas dynamicists eq. nozzle flow 、 flow through wind tunnel & rocket.
16 CHAPTER Thermodynamics of High-Speed Gas Flow.
Rocket Engines Liquid Propellant –Mono propellant Catalysts –Bi-propellant Solid Propellant –Grain Patterns Hybrid Nuclear Electric Performance Energy.
Thrust E80 Static Motor Test Spring Forces on a Rocket
Presenter: Peter Renslow Advisors: James K. Villarreal and Steven Shark.
Example 3.1 Air flows from a reservoir where P = 300 kPa and T = 500 K through a throat to section 1 in Fig. 3.4, where there is a normal – shock wave.
Introduction to Propulsion
Rockets and Launch Vehicles
Uncontrolled copy not subject to amendment Rocketry Revision 1.00.
Title: Intro to Water Bottle Rockets
Discovery of A Strong Discontinuity P M V Subbarao Associate Professor Mechanical Engineering Department I I T Delhi A Break Through Finding To Operate.
Rocket Nomenclature EGR 4347 Analysis and Design of Propulsion Systems.
Hunter, Kevin Yu, Marcus. These Next Few Steps Using the Newton Law of motion and some outside research, we will derive the basic equation that describe.
Class 4: Fundamentals of Rocket Propulsion
HTPB Fuel Grain Flow Rate, Sizing, and Thrust. Regression Rate Governs Size The faster the solid propellant is burned, the “fatter” the rocket must be.
The Thrust Generator P M V Subbarao Professor Mechanical Engineering Department Another Passive Device…… An Obvious Concept for Generation of Motive Power.
Hybrid Rocket Combustion Process & Nozzle John Chambers.
C & CD Nozzles for Jet Propulsion
MAE 4262: ROCKETS AND MISSION ANALYSIS
Jet propulsion and Jet Engines
AE 1350 Lecture Notes #13.
Rocket Engine Physics and Design
Mass Flow Rate M 1 Flow rate out of a tank depends on tank temperature, pressure and size of throat.
Stagnation Properties P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Capacity of A Resource…..
EXTROVERTSpace Propulsion 02 1 Thrust, Rocket Equation, Specific Impulse, Mass Ratio.
Review of Components Analysis Aerospace Engineering, International School of Engineering (ISE) Academic year : (August – December, 2012) Jeerasak.
CP502 Advanced Fluid Mechanics Compressible Flow Lectures 5 and 6 Steady, quasi one-dimensional, isentropic compressible flow of an ideal gas in a variable.
One Dimensional Flow of Blissful Fluid -III P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Always Start with simplest Inventions……..
Rockets. Rocket  A chamber enclosing a gas under pressure  Small opening allows gas to escape providing thrust in the process  Which of Newton’s Laws?
Design of Supersonic Intake / Nozzle P M V Subbarao Associate Professor Mechanical Engineering Department I I T Delhi Meeting the Cruising Conditions…
Rocket Science Modeling the motion of a small rocket using a spreadsheet.
WORK Work = Force x Distance POWER power = work done ÷ time taken ENERGY 1-POTENTIAL ENERGY (Potential Energy = Force x Distance ) 2-KINETIC ENERGY Energy.
Compressive Flow in Nozzles
THE TSIOLKOVSKY ROCKET EQUATION
Stagnation Properties
How Planes and Other Aircrafts Fly
One Dimensional Flow of Blissful Fluid -III
Rockets AND PROJECTILE MOTION.
Analysis of Multistage Rockets
MAE 5380: AIR-BREATHING ENGINE INLETS
PRESENTATION ON HOW A SUPERSONIC WIND TUNNEL WORKS
Gas Dynamics for Design of Nozzles
Figure 2.9 T-s diagram for converging only nozzle
Rocket Engines Liquid Propellant Solid Propellant Hybrid Nuclear
Gas Dynamics for Study of Off-Design
Jet Engines Aerospace.
MAE 5350: Gas Turbines Subsonic and Supersonic Inlets
MAE 5350: Gas Turbines Nozzles
MAE 5380: ROCKETS AND MISSION ANALYSIS
Section 5: Lecture 3 The Optimum Rocket Nozzle
Jet Aircraft Propulsion
Rockets The Rocket Equations LabRat Scientific © 2018.
Rocketry Trajectory Basics
Aerodynamic Stability of Finned Rockets
Rocket Physics The Thrust Curve
Rocket Physics Production of Thrust
Rocket Physics Application of Conservation of Momentum
27. Compressible Flow CH EN 374: Fluid Mechanics.
Motion Newton’s Laws LabRat Scientific © 2018 F = Ma.
Section 5: Lecture 3 The Optimum Rocket Nozzle
Generating Thrust with a Propeller
Model Rockets.
Presentation transcript:

Rocket Physics The Rocket Nozzle LabRat Scientific © 2018

Relevant Concepts to Keep In Mind SUBSONIC Gas Flow Flow velocity is less than the speed of sound (< ~700 MPH) As the area through which the gas is flowing decreases, the flow velocity increases and the pressure decreases The convergent section of a nozzle increases the velocity of the subsonic flow SONIC Gas Flow Where the flow velocity is equal to the speed of sound (= ~700 MPH) By design, this condition occurs at the throat (smallest cross-sectional area in the nozzle) SUPERSONIC Gas Flow Flow velocity is greater than the speed of sound (> ~700 MPH) As the area through which the gas is flowing increases, the flow velocity increases and the pressure decreases The divergent section (a.k.a. exit cone) of the nozzle increases the velocity of the supersonic flow

Thrust Equation 3. Design a nozzle that maximizes the velocity of the gas that is ejected from the motor 1. Increase the total mass that is ejected from the motor Thrust = ((MassPropellant * VelocityExhaust) / Time) + (Pe - Pa) * A 2. Burn the propellant faster (reduce the time period over which the motor burns) From this equation, we can see there are several ways to increase the thrust generated by a rocket motor:

Increasing the Mass Being Ejected from the Rocket Motor The only way to increase the mass is to use a more dense propellant, or increase the amount of propellant. Higher density propellant, or adding more propellant, causes the mass of the rocket motor to increase. While more mass will be ejected and thrust would increase, the rocket motor will be heavier, and F=ma says the rocket will not accelerate as much. Any gain in thrust will generally be offset by the reduction in final velocity due to the lower acceleration. More fuel makes for a more complex motor, and certainly a more expensive one. This is not the solution to maximizing the efficiency of a given rocket motor.

Burning Propellant Faster We can dump more mass out the nozzle faster by burning the propellant quicker… This sounds great, but we have a limited amount of propellant, so as the motor burns faster, the burn time will be shorter. Faster burning propellant will increase acceleration, but since the motor will produce the acceleration over a shorter period, the final velocity will generally not be any higher. Burning all the propellant at once is also know as an explosion! Not good for a rocket… BOOM! This is not the solution to maximizing the efficiency of a given rocket motor.

Increasing the Exhaust Exit Velocity The only option left is to put a nozzle on the back of the motor to accelerate the exhaust gasses leaving the rocket motor. To do this, we need to apply the earlier concepts of subsonic and supersonic gas flows (Slide 2), and design an efficient nozzle that perfectly expands the exhaust gas. Let’s look at the elements of a rocket nozzle and see how it accelerates the exhaust gas.

Elements of the Rocket Nozzle Convergent Section Combustion Chamber Divergent Section Throat Gas wants to move from an area of high pressure to an area of low pressure, so a low velocity flow moves towards the nozzle. Combustion Combustion creates high pressure in the combustion chamber A supersonic flow will increase in velocity as the area gets greater A subsonic flow will increase in velocity as the area gets smaller A nozzle is designed so the flow is at Mach 1 in the throat. It can not be higher, but it can be less… M=1

Elements of the Rocket Nozzle Convergent Section Combustion Chamber Divergent Section Throat Combustion M=1 So, the purpose of a nozzle is to accelerate the flow to its maximum possible velocity…

Elements of the Rocket Nozzle Convergent Section Combustion Chamber Divergent Section Throat Combustion This is achieved when the flow is perfectly expanded. A perfectly expanded flow is where the Exit Pressure (Pe) is equal to the Ambient Pressure (Pa) Pe Pa M=1

Elements of the Rocket Nozzle Convergent Section Combustion Chamber Divergent Section Throat Combustion M=1 Since the Ambient Pressure (Pa) is changing as we fly higher, and the nozzle geometry is fixed, maximum performance is only achieved at one point during the flight…

The Perfectly Expands Gas Flow Thrust = ((Mass * Velocity) / Time) + (Pe - Pa) * A As the exhaust gas moves through the nozzle, the gas pressure decreases. This allows the gas to accelerate (i.e. move faster). If we make the Divergent Section (a.k.a Exit Cone) too short, the flow velocity will not have the opportunity of accelerate the maximum amount before it leaves the nozzle. This means the velocity at the exit plane is not maximized… If we make the Divergent Section (a.k.a Exit Cone) too long, the flow velocity will be too high and the exhaust gas pressure will be less than the atmospheric pressure. This creates a vacuum at the nozzle exit plan. This vacuum tries to suck the motor backwards, reducing the effective thrust.

Let’s look at these concepts using a Pressure/Velocity Plot for the gas moving through a rocket motor…

Generic Pressure and Velocity in a Solid Rocket Motor Combustion Chamber Nozzle Gas Pressure We select the exit cone length such that the gas pressure is equal to the atmospheric pressure. Gas Velocity Represents a vacuum The gas pressure decreases and the velocity increases as the gas moves through the motor

Generic Pressure and Velocity in a Solid Rocket Motor Combustion Chamber Nozzle Exit Cone too short… An exit cone that is too short results in an exit velocity that is not maximized… Gas Pressure Gas Velocity

Generic Pressure and Velocity in a Solid Rocket Motor Combustion Chamber Nozzle Exit Cone too long… Gas Pressure An exit cone that is too long creates a vacuum at exit plane which has the effect of reduced thrust… Gas Velocity

Generic Pressure and Velocity in a Solid Rocket Motor Exit Cone just right… Combustion Chamber Nozzle Gas Pressure Ideal - Velocity maximized and no vacuum at the exit plane. Gas Velocity

Theoretical calculations can be made and the results plotted to demonstrate where the maximum thrust exists…

Maximum thrust occurs when Pe = Pa , and that condition will only happen at one specific altitude for a given nozzle configuration… In this plot, we can see that the Thrust is maximized when Pa = Pe

Questions?