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December 7, 2016, 05:29 |
My radial inflow turbine
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#1 |
New Member
Ahmad Hari
Join Date: Dec 2016
Posts: 21
Rep Power: 9 |
Hello all,
I would first thank you for your Q and A throughout the forum. I've done successful simulation of my radial turbine using other software packages. I also followed the CFX tutorials regarding Axial turbine and centrifugal compressor. However, I'm designing a radial inflow turbine that is not available in the tutorial. As a starting point, I designed a simple rotor blade using RTD and exported it to Turbogrid and then to CFX. The results of CFX is totally different form the RTD. For example the efficiency is 67.7% in RTD while it is 100% in CFX ! I know there is an error somewhere but I can't find it. I'm attaching a link for the dropbox where you can find the saved project (case.wbpj) https://www.dropbox.com/s/1t7zrv15rd...files.zip?dl=0 https://www.dropbox.com/s/06yjmn9ly5...case.wbpj?dl=0 Your suggestions are highly appreciated All the best |
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December 7, 2016, 05:52 |
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#2 |
Senior Member
Maxim
Join Date: Aug 2015
Location: Germany
Posts: 415
Rep Power: 13 |
Hello Fuhaid and welcome to the forums.
I won't download zip-files from random people (and I am not allowed to on my work computer). So please share a few screenshots of your setup and your CCL-file and/or your OUT-file (copy and paste in the CODE environment here). Furthermore I would like to point you to the FAQ: https://www.cfd-online.com/Wiki/Ansy..._inaccurate.3F |
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December 7, 2016, 06:21 |
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#3 |
New Member
Ahmad Hari
Join Date: Dec 2016
Posts: 21
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Hi Maxim,
many thanks for your reply and I understand that you can not open such links. I tried to copy and paste the screenshots but I could not so I uploaded them as jpg picture. I noticed that the results in the CFD post are written as ''Compressor Performance Results) ! CFX Set Up # State file created: 2016/12/07 11:10:00 # CFX-15.0.7 build 2014.04.26-07.00-131803 FLOW: Flow Analysis 1 SOLUTION UNITS: Angle Units = [rad] Length Units = [m] Mass Units = [kg] Solid Angle Units = [sr] Temperature Units = [K] Time Units = [s] END ANALYSIS TYPE: Option = Steady State EXTERNAL SOLVER COUPLING: Option = None END END DOMAIN: R1 Coord Frame = Coord 0 Domain Type = Fluid Location = Inlet,Outlet,Passage Main BOUNDARY: R1 Blade Boundary Type = WALL Frame Type = Rotating Location = BLADE BOUNDARY CONDITIONS: HEAT TRANSFER: Option = Adiabatic END MASS AND MOMENTUM: Option = No Slip Wall END WALL ROUGHNESS: Option = Smooth Wall END END END BOUNDARY: R1 Hub Boundary Type = WALL Frame Type = Rotating Location = INBlock HUB,OUTBlock HUB,Passage HUB BOUNDARY CONDITIONS: HEAT TRANSFER: Option = Adiabatic END MASS AND MOMENTUM: Option = No Slip Wall END WALL ROUGHNESS: Option = Smooth Wall END END END BOUNDARY: R1 Inlet Boundary Type = INLET Frame Type = Stationary Location = INBlock INFLOW BOUNDARY CONDITIONS: FLOW DIRECTION: Option = Normal to Boundary Condition END FLOW REGIME: Option = Subsonic END HEAT TRANSFER: Option = Stationary Frame Total Temperature Stationary Frame Total Temperature = 500 [K] END MASS AND MOMENTUM: Option = Stationary Frame Total Pressure Relative Pressure = 240 [kPa] END TURBULENCE: Option = Medium Intensity and Eddy Viscosity Ratio END END END BOUNDARY: R1 Outlet Boundary Type = OUTLET Frame Type = Stationary Location = OUTBlock OUTFLOW BOUNDARY CONDITIONS: FLOW REGIME: Option = Subsonic END MASS AND MOMENTUM: Mass Flow Rate = 0.03846 [kg s^-1] Option = Mass Flow Rate END END END BOUNDARY: R1 Shroud Boundary Type = WALL Frame Type = Rotating Location = INBlock SHROUD,OUTBlock SHROUD,Passage SHROUD BOUNDARY CONDITIONS: HEAT TRANSFER: Option = Adiabatic END MASS AND MOMENTUM: Option = No Slip Wall WALL VELOCITY: Option = Counter Rotating Wall END END WALL ROUGHNESS: Option = Smooth Wall END END END BOUNDARY: R1 to R1 Internal Side 1 Boundary Type = INTERFACE Location = SHROUD TIP GGI SIDE 1 BOUNDARY CONDITIONS: HEAT TRANSFER: Option = Conservative Interface Flux END MASS AND MOMENTUM: Option = Conservative Interface Flux END TURBULENCE: Option = Conservative Interface Flux END END END BOUNDARY: R1 to R1 Internal Side 2 Boundary Type = INTERFACE Location = SHROUD TIP GGI SIDE 2 BOUNDARY CONDITIONS: HEAT TRANSFER: Option = Conservative Interface Flux END MASS AND MOMENTUM: Option = Conservative Interface Flux END TURBULENCE: Option = Conservative Interface Flux END END END BOUNDARY: R1 to R1 Periodic 1 Side 1 Boundary Type = INTERFACE Location = INBlock PER1 BOUNDARY CONDITIONS: HEAT TRANSFER: Option = Conservative Interface Flux END MASS AND MOMENTUM: Option = Conservative Interface Flux END TURBULENCE: Option = Conservative Interface Flux END END END BOUNDARY: R1 to R1 Periodic 1 Side 2 Boundary Type = INTERFACE Location = INBlock PER2 BOUNDARY CONDITIONS: HEAT TRANSFER: Option = Conservative Interface Flux END MASS AND MOMENTUM: Option = Conservative Interface Flux END TURBULENCE: Option = Conservative Interface Flux END END END BOUNDARY: R1 to R1 Periodic 2 Side 1 Boundary Type = INTERFACE Location = OUTBlock PER1 BOUNDARY CONDITIONS: HEAT TRANSFER: Option = Conservative Interface Flux END MASS AND MOMENTUM: Option = Conservative Interface Flux END TURBULENCE: Option = Conservative Interface Flux END END END BOUNDARY: R1 to R1 Periodic 2 Side 2 Boundary Type = INTERFACE Location = OUTBlock PER2 BOUNDARY CONDITIONS: HEAT TRANSFER: Option = Conservative Interface Flux END MASS AND MOMENTUM: Option = Conservative Interface Flux END TURBULENCE: Option = Conservative Interface Flux END END END BOUNDARY: R1 to R1 Periodic 3 Side 1 Boundary Type = INTERFACE Location = Passage PER1 BOUNDARY CONDITIONS: HEAT TRANSFER: Option = Conservative Interface Flux END MASS AND MOMENTUM: Option = Conservative Interface Flux END TURBULENCE: Option = Conservative Interface Flux END END END BOUNDARY: R1 to R1 Periodic 3 Side 2 Boundary Type = INTERFACE Location = Passage PER2 BOUNDARY CONDITIONS: HEAT TRANSFER: Option = Conservative Interface Flux END MASS AND MOMENTUM: Option = Conservative Interface Flux END TURBULENCE: Option = Conservative Interface Flux END END END DOMAIN MODELS: BUOYANCY MODEL: Option = Non Buoyant END DOMAIN MOTION: Alternate Rotation Model = true Angular Velocity = 60000 [rev min^-1] Option = Rotating AXIS DEFINITION: Option = Coordinate Axis Rotation Axis = Coord 0.3 END END MESH DEFORMATION: Option = None END REFERENCE PRESSURE: Reference Pressure = 0 [Pa] END END FLUID DEFINITION: Air Ideal Gas Material = Air Ideal Gas Option = Material Library MORPHOLOGY: Option = Continuous Fluid END END FLUID MODELS: COMBUSTION MODEL: Option = None END HEAT TRANSFER MODEL: Option = Total Energy END THERMAL RADIATION MODEL: Option = None END TURBULENCE MODEL: Option = SST END TURBULENT WALL FUNCTIONS: High Speed Model = Off Option = Automatic END END END DOMAIN INTERFACE: R1 to R1 Internal Boundary List1 = R1 to R1 Internal Side 1 Boundary List2 = R1 to R1 Internal Side 2 Interface Type = Fluid Fluid INTERFACE MODELS: Option = General Connection FRAME CHANGE: Option = None END MASS AND MOMENTUM: Option = Conservative Interface Flux MOMENTUM INTERFACE MODEL: Option = None END END PITCH CHANGE: Option = None END END MESH CONNECTION: Option = GGI END END DOMAIN INTERFACE: R1 to R1 Periodic 1 Boundary List1 = R1 to R1 Periodic 1 Side 1 Boundary List2 = R1 to R1 Periodic 1 Side 2 Interface Type = Fluid Fluid INTERFACE MODELS: Option = Rotational Periodicity AXIS DEFINITION: Option = Coordinate Axis Rotation Axis = Coord 0.3 END END MESH CONNECTION: Option = Automatic END END DOMAIN INTERFACE: R1 to R1 Periodic 2 Boundary List1 = R1 to R1 Periodic 2 Side 1 Boundary List2 = R1 to R1 Periodic 2 Side 2 Interface Type = Fluid Fluid INTERFACE MODELS: Option = Rotational Periodicity AXIS DEFINITION: Option = Coordinate Axis Rotation Axis = Coord 0.3 END END MESH CONNECTION: Option = Automatic END END DOMAIN INTERFACE: R1 to R1 Periodic 3 Boundary List1 = R1 to R1 Periodic 3 Side 1 Boundary List2 = R1 to R1 Periodic 3 Side 2 Interface Type = Fluid Fluid INTERFACE MODELS: Option = Rotational Periodicity AXIS DEFINITION: Option = Coordinate Axis Rotation Axis = Coord 0.3 END END MESH CONNECTION: Option = Automatic END END OUTPUT CONTROL: MONITOR OBJECTS: EFFICIENCY OUTPUT: Efficiency Calculation Method = Total to Static Efficiency Type = Expansion Inflow Boundary = R1 Inlet Option = Output To Solver Monitor Outflow Boundary = R1 Outlet END MONITOR BALANCES: Option = Full END MONITOR FORCES: Option = Full END MONITOR PARTICLES: Option = Full END MONITOR RESIDUALS: Option = Full END MONITOR TOTALS: Option = Full END END RESULTS: File Compression Level = Default Option = Standard END END SOLVER CONTROL: Turbulence Numerics = High Resolution ADVECTION SCHEME: Option = High Resolution END CONVERGENCE CONTROL: Length Scale Option = Conservative Maximum Number of Iterations = 200 Minimum Number of Iterations = 1 Timescale Control = Auto Timescale Timescale Factor = 1.0 END CONVERGENCE CRITERIA: Residual Target = 1e-06 Residual Type = MAX END DYNAMIC MODEL CONTROL: Global Dynamic Model Control = On END END END COMMAND FILE: Version = 15.0 END |
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December 7, 2016, 06:45 |
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#4 |
Member
Join Date: Nov 2013
Posts: 57
Rep Power: 12 |
Hello,
"Maximum Number of Iterations = 200" most probably your simulation has not been converged yet! |
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December 7, 2016, 06:55 |
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#5 |
New Member
Ahmad Hari
Join Date: Dec 2016
Posts: 21
Rep Power: 9 |
Hello alirezame,
I set the maximum number of iterations to 3000 but I got same results with a very slight difference in the efficiency. |
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December 7, 2016, 10:02 |
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#6 |
Senior Member
Join Date: Jun 2009
Posts: 174
Rep Power: 17 |
Check your inlet swirl BC in CFX. It shows zero swirl, while your design wants 70 deg swirl.
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December 7, 2016, 12:20 |
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#7 |
New Member
Ahmad Hari
Join Date: Dec 2016
Posts: 21
Rep Power: 9 |
Hi Turbo,
Many thanks for your reply. Is it possible to paly with the swirl angle in CFX? would you please show me how to change the angle from 0 to 70? |
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December 7, 2016, 12:32 |
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#8 |
Senior Member
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December 7, 2016, 13:12 |
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#9 |
New Member
Ahmad Hari
Join Date: Dec 2016
Posts: 21
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Hi Antanas,
Thank you for your reply. are the X Y Z components are simply U W V, respectively? |
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December 7, 2016, 13:37 |
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#10 |
Member
turbo4life
Join Date: Nov 2016
Posts: 41
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Please provide some screenshots from CFX-Pre so I can see your model. Also please answer the following:
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December 7, 2016, 13:58 |
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#11 | |
New Member
Ahmad Hari
Join Date: Dec 2016
Posts: 21
Rep Power: 9 |
Quote:
Hi bparrelli, Many thanks for your reply. 1. Only rotor 2. Single passage 3. I'm applying: inlet total pressure, inlet total temperature, and mass flow rate. 4. inlet total temp is 500K and inlet total pressure is 240 KPa 5. PR = 2.2 6. Ideal gas air 7. impeller wheel and speed are 86.041 mm and 60000 rpm I uploaded the CCl file of the CFX pre in Maxim. I also attached the screenshot |
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December 7, 2016, 14:54 |
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#12 | |
Member
turbo4life
Join Date: Nov 2016
Posts: 41
Rep Power: 9 |
Quote:
Also, your inlet conditions are fine, but if you're going to model the rotor without a nozzle, then you need to specify the nozzle swirl. Right now, you have the absolute velocity coming in normal to the rotor inlet boundary. This is fine if you're solving the problem in the relative frame, but I don't think you are. I have had convergence trouble modelling high inlet swirl in this type of problem before, and you may just have to model the nozzle with the rotor together to make it work. At a minimum, the models for my designs have a nozzle and a rotor modeled together. In reality, the flow coming into the rotor will be very non-uniform due to nozzle/rotor interaction, and employing inlet swirl is not sufficient to capture this effect. The only way to get the full physics, is to model the nozzle and rotor together with a mixing plane (stage) interface. If this is not an option at this time fore you, I would recommend calculating the flow parameters in the relative frame, and solving your rotor as a stationary nozzle. Lastly, you want to use the pressures as your boundary conditions, not mass flow. This will give you more stable convergence. Your turbine U/C0 is only about 0.4, so your efficiency should not be very high (maybe 50-70%). Try all this and let me know if that helps. |
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December 7, 2016, 19:33 |
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#13 |
New Member
Ahmad Hari
Join Date: Dec 2016
Posts: 21
Rep Power: 9 |
Dear Brian,
Many thanks for your detailed reply. That's highly appreciated. I will try modelling both stator and rotor. But before that, could you please advise how to set the swirl angle in case of vsnelss rotor as the one I did? I think I can do it by setting the Cartesian coordinate instead of choosing normal to boundary. If this is the case, are x y z components mean simply u w v ? Also, I sent you a private message. Would you kindly check it? All the best |
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December 7, 2016, 22:40 |
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#14 |
Member
turbo4life
Join Date: Nov 2016
Posts: 41
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Yes, but I'd recommend using cylindrical coordinates, as they're more appropriate for turbomachinery. I don't answer private messages, sorry. But if you're interested in my course, you can access it at the link in my signature below. There is also a webinar about the course tomorrow morning at 8am PST. You can sign up for it on the SolidProfessor website.
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December 8, 2016, 05:45 |
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#15 |
New Member
Ahmad Hari
Join Date: Dec 2016
Posts: 21
Rep Power: 9 |
Thank you Brian. I'm keen to register in the courses.
I Know I asked many questions but hopefully this will be my last question: I have the following velocity components at the rotor inlet, how can I convert them to cylindrical coordinates ( Axial component, Radial component and Theta component)? U (Blade Speed)= 270.3 m/s, W (Relative Velocity)= 96.1 m/s, V2 (Absolute Velocity)= 280.4 m/s Vr (Radial Velocity) = 95.9 m/s Vw (Whirl Velocity) = 263.5 m/s Many thanks |
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December 8, 2016, 09:37 |
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#16 |
Senior Member
Join Date: Jun 2009
Posts: 174
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You can go ahead without nozzle solving the rotor only.
Note CFX inlet swirl BC notations are different from turbomachinery velocity notations. The "u" is a unit vector of x-direction, "v" for y and "w" for z-direction, respectively. If your machine rotation axis is z-direction, w = 0.0 (implying no axial flow at the rotor inlet) u = -1.0 (implying downward inflow) v = + tan 70 deg |
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December 8, 2016, 10:31 |
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#17 |
Member
turbo4life
Join Date: Nov 2016
Posts: 41
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If z is the rotation axis, then you can define it as follows:
axial coordinate = z r = sqrt(x^2+y^2) x = r*cos(theta) y = r*sin(theta) This is very basic stuff that you should find in many math textbooks. |
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December 11, 2016, 15:14 |
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#18 |
New Member
Ahmad Hari
Join Date: Dec 2016
Posts: 21
Rep Power: 9 |
Dear Turbo and Brian,
Thank you for the continuous support. I spent the weekend working on a new rotor blade but each time I got wrong results such as 100% total to static efficiency, lower mass flow rate values etc. I also don't know why it shows '' Compressor'' instead of turbine in the tabulated results. I attached a link for my simulation and I also attached photos for those who don't to open anonymous links. I would be very happy if you take a look at it and advise me https://www.dropbox.com/s/qe8wsiv4cdlowp1/Try.zip?dl=0 |
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December 11, 2016, 15:15 |
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#19 |
New Member
Ahmad Hari
Join Date: Dec 2016
Posts: 21
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Continue of the attached photos
Just to let you, I'm using Cartesian coordinates based on comment by Turbo. I have a swirl angle (absolute flow angle) = 78.33 deg Many thanks in advance |
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December 11, 2016, 18:57 |
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#20 |
Member
turbo4life
Join Date: Nov 2016
Posts: 41
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A few thoughts:
1. Did you make sure your direction of rotation is correct using the right hand rule? 2. You should calculate the rotor efficiency on your own. Don't rely on the tabulated results. You aren't modeling the nozzle so your total isentropic enthalpy drop across the turbine isn't captured. In any case, the correct way to calculate turbine efficiency is: (Rotor torque x RPM) / (mdot*deltaHs) I'll leave it to you to work out the units. |
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