CFD analysis of thrust vectoring nozzle

Abstract

Today, thrust vectoring has become very important research subject which can dramatically change the way aircraft maneuvering in the future and their performance .It can control vehicles attitude and flight path, so it reduces the dependability on the primary control surfaces .We will do flow analysis through deflecting nozzle at different angles and by that we determine aerodynamic coefficients .And then we'll get optimum angles from different maneuvering positions.

Introduction

 flow analysis of thrust vectoring nozzle, this work will help to know the effects of thrust vectoring nozzle on engine flow and parameters.

EFFECT

Thrust vectoring can control vehicles attitude and flight path and it reduces the dependability on the primary control surfaces so, flow analysis of thrust vectoring helps to know their performance.

Objective of thrust vectoring

·     To give higher maneuvering and agility to aircrafts.

·     To decrease dependability on aero parts.

Reference

I had taken SATURN AL-31 engine as reference for thrust vectoring nozzle.

How thrust vectoring nozzle is working?

There are many ways for vectoring of thrust but we choose engine having three ring system for thrust vectoring analysis. Three ring system is controlled by 4 actuators, By moving of ring forward and backward yawing and pitching of aircraft is controlled. (For three ring system we had taken reference of “Thrust Vectoring Nozzle for Modern Military Aircraft”

By Daniel Ikaza)

Data from SATRUN AL-31

›      Ring diameter: 660mm

›      Ring length:150mm

›      Flap section total length:433mm

›      Nozzle diameter:630mm

›      Nozzle total length:853mm

›      Turbine inlet temperature: 1685K

›      Overall pressure ratio: 23

From that data and basic propulsion techniques we had calculated,

Nozzle inlet temperature: 774.268K

Pressure at nozzle inlet: 102000pa

Modeling

We had used CATIA software for modeling of geometry and created thrust vectoring nozzle.

From here flaps aren’t used for analysis. Then we had make 7 different geometries those are at

      I.            Maximum thrust condition

   II.            15’ nozzle flaps deflection

III.            10’ nozzle flaps deflection

IV.            Pitch up

   V.            Pitch down

VI.            Moving right

VII.            Moving left

As three ring system used for controlling flaps will not affect individually they functions as a whole unit and the area created by that unit is directly affect the flow.

Meshing

We had used ANSYS software for meshing of model, meshing is required for discretization of model for CFD analysis.

 

No. of nodes: 88283

No. of elements: 462511

Mesh quality

Quality of generated mesh plays significant role in numerical computation, mesh quality can checked from skewness, orthogonal quality, and aspect ratio of mesh.

Skewness

Mesh skewness is one of the most important features that determines the quality of mesh, skewness is basically defined on the geometrical orientation of a mesh.

Skewness tends to zero indicates good quality of mesh. And as per chart most of elements having skewness nearer to zero mesh quality is good.

Grid independency test

Solution of CFD problem relay on mesh, so such mesh resolution required in which solution is independent from mesh resolution. This test gives best mesh resolution which is compatible for solution,

In our case we had calculated the solution for different element sizing of 20mm, 15mm, 10mm, 5mm

Element size	No of elements	Jet exit velocity
20mm	142602	599.524 m/s
15mm	191455	601.36 m/s
10mm	462511	602.38 m/s
5mm	2071558	602.41 m/s

The values at element size of 10mm and 5mm are nearly same so we can say that at 10mm element size solution is independent from mesh resolution.

Equation of thrust

Thrust can be calculated by,

T= (Ma+Mf)*Vj   -   (Ma)*Vi

Vj =jet exit velocity

Ma =mass flow rate of air

Mf =mass flow rate of fuel

Vi =engine inlet velocity

Solution

Vector contours for maximum thrust design

Pressure

Shear

Velocity

Vector contour for pitch up design

Pressure

Shear

Velocity

From these vector contours we can get idea about pressure, shear and velocity distribution over the nozzle in different maneuvering positions.

Results

Nozzle inlet temperature is 774K and nozzle inlet pressure is 102000Pa, for getting results of thrust we had obtained value of Ma and Mf theoretically by jet propulsion techniques.

Ma=148.6758 kg/s

Mf=4.078 kg/s

Position	Cd	Cl	Jet exit velocity(Vj)	Thrust force by nozzle	Force Perpendicular to axis  by nozzle
Maximum thrust 20’	0.583	0.000326	602 m/s	74.5kN	0kN
Nozzle flaps angle15’	0.599	0.000069	402 m/s	43.948kN	0kN
Nozzle flaps angle10’	0.746	0.000011	274.8 m/s	24.517kN	0kN
Pitching up	0.899	-0.759	628.2 m/s	71.7kN	31.93kN(in +Y direction causes lift)
Pitching down	1.10	0.718	625.6 m/s	71.7kN	31.93kN(in -Y direction causes lift)
Moving right	0.295	0.000262	628.2 m/s	71.7kN	31.93kN(in +X direction causes yaw)
Moving left	1.172	0.000282	628.2 m/s	71.7kN	31.93(in -X direction causes yaw)

Here, graph relates jet exit velocity at different nozzle deflection angle

Conclusion

·     From these project we had calculated the values of lift coefficients, drag coefficients, thrust, lifting and yawing forces for different maneuverings positions.

·     Maximum thrust can obtains at very low aircraft velocity of 118m/s so it is beneficial for fighter aircraft.

·     Maximum thrust can obtains at 20’ nozzle deflection so that is optimum angle.

·     Vectoring of flow creates a force in flight direction and as well as in yaw/lift direction that causes moving in that direction.

Literature references

›      E.A. Wilson,D.Alder and P.Z. Bar-Joseph., “Axisymmetric Thrust-vectoring nozzle performance prediction”

›      “From their study on performance of TV nozzle, they calculated dynamic TV-nozzle geometry and performances at the critical flow point, so it can be use in future TV-nozzle design to reduce costly experimental investigations, may be implemented for TV-nozzle performances to enhance defense simulation, as well as provide initial conditions for numerical VSTOL/TV jet performance studies.”

›      Daniel Ikaza “Thrust Vectoring nozzle for military aircraft engines”

›      “From his study we get information about ITP’s thrust vectoring nozzle program and also get information about mechanical actuation of thrust vector nozzle”.