2 Design Radial Inflow Turbine Using Rital

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© 2010 Concepts ETI, Inc. The material contained herein is proprietary and confidential. All rights reserved.

Design Radial Inlet Turbine

using RITAL™

Shuo Li, Ph.D.

Sr. Engineering Software Trainer/

Project Manager

Concepts NREC

The material contained herein is proprietary and confidential

© 2010 Concepts ETI, Inc. All rights reserved. •2

AgileTM Engineering Design System®

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Share the same user interface with other CN radial meanline

programs

Rital™ GUI 1



File: RITAL™ program setup

Agile: links to other Agile system programs

Standard Screens: predefined screen layouts, user

customable

Setup: general design settings, including unit system, mode,

models…etc.

Components: for current stages, detailed setting/input of

each component

Solver: run the solver and its settings

RITAL™ GUI 2

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Toolbar

Program setup

Exercise

Start RITAL™ and open an example from installation directory, e.g.,

\examples\tutorial\turbine01.geo

Explore the menu system and complete the following:

1. Basic program setup, such as preferences, unit system, etc.

2. View current design layout, find out settings for each component

3. Run the solver, view text report and display tip velocity triangle at impeller exit

4. Try some standard screen views

RITAL™ GUI 3



Station Number

0 Scroll inlet

1 Scroll exit

2 Nozzle throat

3 Nozzle exit

4 Rotor inlet

5 Rotor throat

6 Rotor exit

7 Diffuser exit

A RITAL™ Stage

Volute

Nozzle

Inter-space

Rotor

Diffuser

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Identify the flow pattern Subsonic

Nozzle choke only

Rotor choke only

Both nozzle and rotor choked

Solve different flow patterns accordingly

Analysis Mode

Design Mode

Design volute throat Subsonic

Set the nozzle vane exit angle

Preliminary sizing



RITAL solver: mass based subsonic solver with real gas

modeling.

RITDAP solver: transonic solver with ideal gas model,

original NREC solver

RTP solver (recommended)

Transonic flow;

Real gas model;

Pressure is adjusted for each station to balance the mass flow for

each component

No mixing calculated, blockage preserved

Choosing Solvers

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Calculate the critical pressures that allow nozzle and

rotor to choke.

Based on the critical pressure, identify the flow patterns:

Subsonic;

Rotor choked only;

Nozzle choked only;

Both nozzle and rotor are choked.

Solve according to different flow patterns.

Improved preliminary sizing by scaling up and down

nozzle blade height addition to throat area adjustment

(2010 release)

Basic Computation Algorithm



Two approaches with little difference:

RITADP approach using optimum specific speed and blade-to-jet ratio

Approach based on the optimum flow coefficient and head coefficient

Assuming a rotor meridional ratio and zero rotor exit swirl, the velocity

triangle can be established

Rotor inlet angel can be set with a specified incidence

Through mass conservation, the blade inlet width can be determined

With the flow coefficient and the assumption of zero exit swirl, the rotor

exit flow area and hub tip radius, can be calculated,

blade angle can be obtained with an assumed deviation angle

Axial length to inlet tip ratio is set as:

AxLen/R4 = 0.6, if R6s/R4 > 0.7

AxLen/R4 = 0.4, if R6s/R4 > 0.4

Linear interpolation is used between values.

Preliminary Sizing Algorithm

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Blade thickness is assumed to be 2% of tip radius and clearance is set

as 1% of the inlet blade height

Nozzle exit radius to rotor inlet radius ratio is set as 1.05, the velocity

triangle could be determined from mass and angular momentum

conservation from rotor inlet.

Blade angle is set assuming 2 degree deviation angle

Nozzle exit to nozzle inlet radius ratio is set as 1.25, straight blade inlet is

assumed (inlet blade angle is zero)

Volute throat radius location and area are calculated as:

A0/r0 = (A/r1)/tan(α1)

R0=r1+(A0/π)1/2 + clearance (1% of R4, 5% of R5 for nozzleless turbine)

Diffuser is assumed to have an area ratio 1.5, divergence angle of

4.5 and R5h = 0, then the rest can be calculated as following:

R5s = (A5/π+R5h2)1/2

ALen_Dif= (R5s-R4s)/tan (DivAng)

Preliminary Sizing Algorithm



Variable Default Value Definition 0.25 Optimum flow coefficient

0.9 Optimum loading coefficient

1.0 Rotor meridional velocity ratio

C6 0 Rotor exit swirl

6 5 Rotor deviation angle

R4h/R3 0.3 Ratio of rotor exit hub radius to rotor inlet radius.

R1/R2 1.25 Ratio of nozzle inlet radius to nozzle exit radius.

R5h 0 Diffuser exit hub radius.

A5/A4 1.5 Area ratio of diffuser exit to inlet.

DivAng 4.5 Diffuser divergence angle.

Preliminary Sizing Default Variables

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Gross or bulk overall coefficients (e.g. rotor efficiency)

Simple functions of operating parameters

Correlated coefficients

Functions of key design parameters

Fundamental or physics-based coefficients

Break loss into components

Model each as function of relevant parameters

BUT

There are only a limited number of datasets available

It is not possible to separate the effects of different loss mechanisms

in the available data

Division is artificial anyway: all losses are interrelated

Loss model categorization



Divide loss into its

likely mechanisms

Correlate each

separately

Breakdown of losses

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Nozzle

Loss: modified Rodgers loss model

Deviation: modified cosine or Howell correlations.

Rotor modeling:

Incidence

Passage (friction, secondary flow, etc.)

Trailing edge

Tip clearance

Supersonic expansion (shock loss)

Windage (leakage loss)

Nozzle and Rotor Modeling



Nozzle loss model:

Rogers Loss Model

Nozzle deviation

Modified Cosine rule

Modified Howell Correlation

Nozzle Models

3

0.2

3sin0.05 b

b

o

s c bRe

For M3 < 0.3, 1

3 0 1cosa a o s

For M3 > 0.3, 1

3 0 1 2 3cos 0.3a a o s a M

1 3

3 3 3 3 1b b b

N

r ra

Z c

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NASA model Friction loss

Passage loss

1 2 2 24 62cospL K W i W

21

2f fL C L D W

2

2 25 54 5

4 5

cos 10.68 1

2

bHp p

H

rLL K W W

D r b c

Profile (friction) loss Secondary flow loss

Due to change in

radius

Due to blade

turning



Leakage flow:

Mainstream flow:

Clearance loss:

Tip clearance loss

1

4 4 4 6 6 6 42L x x t t r r Rm U K r r U K z b Z

4 4 4 4 5 6 6 62 2m mm C r b C r b

1 2

2c LL m m U

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Tip clearance loss

34

8

Rc x x x r r r xr x r x r

U ZL K C K C K C C

Axial

clearance

coefficient

Radial

clearance

coefficient

“Cross-

coupling”

coefficient

Trailing edge loss

2

05 06 6

05 5 5

1 m

m

p p C

p p C

•20The material contained herein is proprietary and confidential

© 2010 Concepts ETI, Inc. All rights reserved.

Windage loss

2 21fric 44f

K r

0.1

4 5

0.5

0.1

4 5

0.2

3.710

0.10210

f

f

rK Re

Re

rK Re

Re

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Free vortex:

Continuity:

Uniform mass flow:

Simple volute model

constantrC K

m A C

12

m m

112

A m

r K



Exit flow angle:

Free vortex and

continuity:

Simple volute model

1 1 1tan mC C

1 0 0 1 0 0 1

0 01 0

1 1 1 1

m

C C r r C r r

r AmC C

r A r A

1 11

1

0 0 0

tanA r

A r

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Blockage

Swirl coefficient

Total pressure loss coefficient

Refining the simple model

1 1 1 1(1 ) mm A B C

1 1 0 0rC Sr C

00 01

01 1

p pK

p p



Real gas calculation is supported in RITAL as well as

AxCent and pbCFD.

About 79 hydrocarbons and 27 refrigerants, as well as

their mixtures, are supported by DBR or NIST.

Mollier table allows user to specify the gas property for

the special fluid that’s not supported in RITAL.

Real Gas Computation

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The RITAL design can be

conveniently passed to AxCent

through Agile link. A three-

dimensional flow-path and

blade geometry is literally one

click away.

If a 3D blade geometry is

available in AxCent, the reverse

Agile link allows easy setup of

RITAL model.

Agile Link



Python Script: How Does It Work?

CETI model

Python script

User model

Has Script?No

Yes

Hook

Rital

• Concepts NREC will provide charged or uncharged Python hooks to customers.

• Customers are responsible for their own script implementation.

Input Output

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Analysis mode allows performance map prediction

of an existing design.

Different analysis types available

Real gas, transonic flow analysis, which allows

multiple components running at the choking condition.

Multiple point analysis and map generation.

Easy comparison with the test data through map

overlay.

Analysis Mode



Choose basic analysis mode, metric unit system

Inlet conditions: P00=130 KPa T00=323 K

Mass flow=0.8 Kg/s N= 11000

Choose new semi-perfect air

Has both volute and nozzle

Volute: area= 10900 mm2 radius= 233 mm

Nozzle: Inlet radius=150mm Exit radius= 140mm

inlet blade height= 26mm Exit blade height= 26mm

inlet inclination angle=-90 number of blades=16

Tip clearance= 0 TE thickness= 0.5mm

Exit blade angle= 79.5

New design wizard: Analysis mode

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Rotor

Inlet radius= 125mm Inlet blade height= 26mm

Exit radius= 40mm Exit blade height= 60mm

Inlet inclination angle= -90 Number of blades= 13

Exit inclination angle= 0 TE normal thickness= 3mm

Axial length= 90mm Axial clearance= 0.5mm

Radial length= 0.5mm Inlet blade angle= 0 deg

Exit blade angle= -54 deg

Don’t run solver and not save

New design wizard: Analysis mode



Analysis Mode: Results Check

Output overview

Text output

Table output

Output filter

Use filters

Create your own filter

View velocity triangles

Plots in Rital®

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Single point analysis

Option to specify mass flow (basic analysis mode), calculate exit

pressure

Option to specify exit pressure (static or total) , calculate inlet

pressure, mass flow or rotational speed

Multiple point analysis

Specify the expansion ratio (total or static)

Option to specify inlet pressure or exit pressure

Up to 12 flow points

Up to 8 values of the selected dependent variable

Exercises :

Check the output of the design we just finished: identify the design

point data set, check geometry of impeller and summary of the stage

Create an output filter you want to use later and save it

Analysis mode



Design Mode: Preliminary design

To set basic geometry of a radial-inflow turbine stage based on some

user-specified design requirements

User specifies three out of four of following parameters: inlet total

pressure, exit static pressure, mass flow rate or stage power output.

Rotational speed may be calculated from the optimum specific

speed. Blade tip speed can be specified if desired.

The design algorithm can be based on the flow and loading

coefficient,.

= CM6/U4 , default value 0.25

=

or the specific speed and speed (blade-to-jet) ratio.

2

40

2

40 // UhUh sts

s

sh

QRPMN

0

6

60

2

sj hUCU 044 2//

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Design Mode: Preliminary design

If RPM is going to be calculated, it is calculated as:

Volute throat or nozzle exit vane angle calculation.

With both mass flow rate and the stage expansion

ratio specified, the program calculates the volute

throat area and the exit vane angle.

A friendly design wizard helps you going through the

necessary input to set up the preliminary sizing.

6

4/3

030

Q

hNRPM ss



Choose RTP solver, Preliminary design

Choose metric unit system

Inlet input:

T00= 400K P00= 186 kPa Pexit= 101.3 kPa m=0.65 kg/s

Choose ideal gas

Choose based on flow coefficient (=0.25) and loading coefficient (0.92)

Choose volute and nozzle

For nozzle: R2/R3=1.25, R3/R4=1.05, number of blades= 15

Calculate blade tip speed, number of blades=12, hub to tip ratio=0.3,

rotor deviation angle 3 degree

Don’t run the solver and not save

Run the solver

Check results

New Design Wizard: Preliminary Design

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Input Pexit or P0exit to calculate nozzle exit blade angle or

volute area

Input power and Pexit or P0exit to calculate mass flow rate

and nozzle exit blade angle or volute area

Example:

Based on the previous completed examples choose design mode of

input power and Pexit to calculate mass flow rate and nozzle exit

blade angle or volute area

Specify the power target as 50 KW

Check results

Compare with previous design

Design modes other than preliminary sizing

2 Design Radial Inflow Turbine Using Rital

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