Wednesday, December 11, 2013

Through 180-Degree Angle of Attack

Following the 1981 paper,  "Aerodynamic Characteristics of Seven Symmetrical Airfoil Sections Through 180 Degree Angle of Attack for Use in Aerodynamic Analysis of Vertical Axis Wind Turbines", Sand80, by Robert E. Sheldahl, et. al., I analyzed the NACA 0012 in MultiElement Airfoils at various angles past stall.

The following picture shows the results of the analysis superimposed on a graphs from the Sandia study.

Analysis of a NACA 0012 airfoil through 180 degrees angle of attack.
The blue dots are the Navier-Stokes solution in MultiElement Airfoils.
  The red Xs are the potentialflow/boundary layer solution.

For the analysis, I used the laminar Navier-Stokes solution setting in MultiElement Airfoils.  The software is based on a Cartesian grid methods (ghost cell approach for the boundary conditions) and has a variety of flow solvers.   The following picture shows the flow at 5 degrees angle of attack.

Analysis of NACA 0012 in MultiElement Airfoils 5.1

More information about MultiElement Airfoils can be found at http://www.hanleyinnovations.com/mefoil.html

Thanks for reading.

Thursday, November 28, 2013

5 Things you can do with a Cartesian grid.

Cartesian grids are very easy to draw. They are quite straight-forward and quick to construct.  Here are five things that one can do with a Cartesian grid.

1. Tic Tac Toe
Are you on a long airplane trip.  Need a quick game? 
Tic Tac Toe grid from Optometry Student website


Of course there are more complex Cartesian grid games such as checkers and chess.

2. Graphs
If you need to quickly display data, then this is the old-school way to do it.  Plot the points and connect the dots.

 
3. Construction and Flooring
Just think about it.  How long would it take to tile your floors if you could not just do this (see pic).

Graph from Wikipedia

4. Mosaics
A form of rasterisation, mosaics can be used to represent pictures of people, objects and places. 
Mosaic of Bob Marley from Art-Heist
 
Digital cameras also use rasterisation to take quick pictures of events, vacation and family gatherings. Leonardo da Vinci would argue that there are better ways of painting pictures. 
 
5. Aerodynamics
Cartesian grids can be used to quickly obtain aerodynamics results for 2-D and 3-D problems if you can solve the boundary problems (without using cut-cells).

Computations using MultiElement Airfoils and Stallion 3D.
 
Fortunately, if you visit http://www.hanleyinnovations.com, you can find the software to easily determine the workings of you CAD creations.

Thanks for reading.

Friday, September 6, 2013

If You Like Jets and Aerodynamics ...

If you like jets, aerodynamics and have a CFD program, you might find yourself doing this:

Yesterday, I visited the NASA OpenVSP Hangar website and saw a model of the Lockheed L-1011.  Because I like the L-1011, I decided to analyze it in Stallion 3D in ground effect  .... (Why not?)

This is how the model loaded in my copy of OpenVSP:

 
 
This is the window that I used  to import the .STL file of the model into Stallion 3D using the Design menu and the Import/Edit .STL file option:


This is a wireframe of the model after it loaded into Stallion 3D.  I set the ground plane option because I wanted to simulate takeoff:

 
 I used the following window to set the resolution of the Cartesian grid in Stallion 3D.  The initial grid in (x,y,z) sub-divisions is (6X2X6):


I opted to use the compressible Euler code for the analysis:


I used the following window to set the ground effect option in the analysis:


After choosing a speed of 100 m/s and a rotation angle of 5 degrees, I clicked the CFD Solver menu and choose Generate Grid/Solve Flow to automatically generate the grid and solve the flow.  I then walked away from my laptop.


I generated this picture (the colors show surface pressure) of the airplane and the ground plane after I returned to the laptop (about 8 hours later):


I rotated the view, changed the display to surface velocity and generated this picture of the aircraft and the ground plane (the colors show velocity):


I thought this picture of the tip airfoil might be interesting.  I also generated the pressure coefficient (Cp) at various stations along the  wing using the Graphs menu and the Pressure Coefficient (Cp) option in Stallion 3D (the colors show pressure).


Granted the OpenVSP model of the L-1011 is not the one sold by Lockheed (airfoils?, plain flaps during takeoff? exposed duct?, etc...), it is still fun to look at the numbers.   The model that I ran measured about 180 feet in length and had a width (wing span) of about 150 feet.

Rotated at 5 degrees during takeoff, here are a few calculations of the lift:
@ 100 mph  --- Lift = 110,000 pounds
@ 150 mph  --- Lift = 245,000 pounds
@ 200 mph  --- Lift = 435,000 pounds
@ 250 mph  --- Lift = 680,000 pounds

Note (mph) is miles per hour.  It will be a good exercise for the reader (I did it myself) to google the performance of the various models of the L-1011 for comparison.

More information about Stallion 3D can be found at http://www.hanleyinnovations.com/stallion3d.html.

Thanks for reading.

Friday, June 14, 2013

5 Things a Superhuman Can Teach Us About Aerodynamics

A superhuman (for example Superman a.k.a. Man of Steel and fathers <Happy Father's Day> ) does not need aerodynamics to fly.  In fact,  the atmosphere can often be an annoyance when speeding to a rescue.

Here are 5 thing a superhuman can teach us about aerodynamics.

1. Use your superhuman ability to levitate if you wish to fly slowly during search and rescue missions.  Flying at a speed of 20 m/s, even with feet down to simulate a Gurney flap, will generate a miniscule 4 pounds of lift from the atmosphere. 

Stallion 3D analysis of superhuman. V=20 m/s
Stl from Turbosquid.com.
 
2. Superhuman strength is required to fly fast as well.  Traveling to a rescue at the reasonable speed of 600 m/s develops upwards of 12,500 pounds of pressure drag which you can tax your super abilities.

 
Flight at 600 m/s.
 
3. Forget the hairdo.  Flying on a humid day causes condensation that can reveal your position and have the bad guys laugh at your vapor made tutu.


Superhuman lifts off. Speeds are 100, 200, 300,
400 and 600 meters per second.

4.  The atmosphere can afford you a jump on the uninitiated bad guys.  Your secret weapon is called Mdd (drag divergence Mach number).   Those new to Earth will be temporarily baffled by their sudden lack-luster performance at or around Mach one.

Drag divergence at around 300 m/s

5.  Aerodynamics is fun! Try it.  BTW, you might need Stallion 3D.

More information about Stallion 3D can be found at http://www.hanleyinnovations.com

Thanks for reading and Happy Father's Day to everyone.

Thursday, June 13, 2013

The Best Airfoil ...

Which NACA airfoil is the best? (for you?) The answer one expects is the shape with the highest lift, lowest drag and most favorable moments. 

Cl vs. Cd for 3 NACA airfoil shapes.
  
The graph above (lift vs. drag) can give us some hints.

  1. The 63-012 is good (low drag) at low lift requirements.  Perfect for a high performance keel (perhaps low aspect ratio).
  2.  The 0012 is good (low drag) at higher lift than the 63-012.  This would work well for a higher aspect ratio keel or rudder.
  3. The 23012 is good for a wing or hydrofoil. It also had good moment characteristics (not shown on graph).
If you have questions about the performance of NACA airfoils and you need to get the coordinates or .DXF file for your designs, then I recommend the VisualFoil NACA software for Windows XP, 7 and 8. 

Thanks for reading.

Some Assembly... (I mean) .. CFD Required .....

If you are in the market for furniture and see the words "some assembly required" things can get a bit scary.  They are even more petrifying when your starting point is at the Home Depot lumber department. The same can be true for computational fluid dynamics a.k.a. CFD, math, fluid dynamics, "rocket science". 

If you are designing an airplane, CFD can be a tremendous help and time-saving tool.  However, if it takes you months to learn, weeks to grid a respectable geometry and produces "fuzzy math" as the solutions then you will not "save time and money".

Luckily the phrase "some assembly required" often means that your only tool is a screw-driver. If you have teenagers, it means that your only task is just to buy the bookshelf.

The same applies to Stallion 3D,  our easy-to-use vertical analysis tool for external aerodynamics. 

To analyze your airplane design, simply import your 3D CAD model into the program:

Step 1. Import CAD drawing of
Cessna from openVSP.

Next, the difficult part ("some CFD required") is to choose the grid size. Small for quick exploratory analysis and large to check your solutions.

Step 2.  Choose a grid size

The next step is to test how well your design performs at specific flight conditions.  You enter speed, angle of attack and side-slip angles.

Step 3.  Enter speed, angle of attack and sideslip.

Like your teenager, Stallion 3D will do all the assembly work for you.  It will automatically generate the grid and analyze the flow field.

Step 4.  Simply click the generate grid/solve flow menu.

After a few hours (depending on the computer/laptop speed and grid size), you can see the results in meaningful numbers (lift, drag, moments or the coefficients).

Step 5. Look at the results and assess the performance of your design.

The idea here is that Stallion 3D is an aerodynamics software that uses powerful built-in CFD tools.  Designers and engineers use the software to analyze concepts and choose the most promising to move forward in the project.

More information about Stallion 3D can be found at http://www.hanleyinnovations.com.

Do not hesitate to email or telephone us at (352) 240-3658 if you have questions.

Thanks for reading.

Sunday, May 26, 2013

Aerospace Capstone Design Projects Should not Stop at Slow

Years ago, I completed my bachelor's degree in aerospace engineering.  Back then, the fastest computers that I had ready access to was my Commodore 64 and of course my HP-4-CV. I used my C64 to work on a rocket staging assignment for in my senior year.  I wrote a partial differential solution (heat equation) for the CV.

NASA BWB Concept at v=290 m/s. Stl file from NASA OpenVSP.

Today, personal computers, laptops and even phones are extremely fast.  However, engineering student are forced to limit exciting design projects such as passenger jets and  futuristic supersonic transports to the conceptual design phase of subsonic flight.  The main reason for this is that current analysis tools such as CFD software can take too long for students to master over one or two semesters when faced with additional obligations such as non-engineering courses, part time jobs and other graduation requirements.

Aerospace engineering should be fun (because it is).  A quick and easy tool can help students design and analyze (on their own) race cars, jets, UAVs, and other vehicles.  It can help them to determine how delta wings of various shapes work at different angles of attack and even at supersonic speeds.

AR=2,  100 m/s at 25 deg. angle of attack (pressure).

AR=1, 100 m/s at 25 deg. angle of attack (pressure).

AR 2, 670 m/s, 25 deg angle of attack (pressure).

Over the last few years, we developed a few computer programs to help students get more out of their design projects.  The latest of these programs is Stallion 3D.

Even with time constraints, students can use their personal computers to take designs to the next speed. Using Stallion 3D, it only takes about one minute to setup a jet for analysis on a laptop computer.


The analysis can be completed (about 6 hours for 500K cells) while they use their computer for other assignments or get valuable sleep.

Stallion 3D works well with other tools available to the student (suchs as NASA's OpenVSP).   The following video shows how the two can work together.



The whole idea of Stallion 3D is to accelerate aerospace engineering education to any speed or at least to move as fast as a cow.

Cow in ground effect at M=1.6

Cow with store (M=1.6)

More information can be obtained from http://www.hanleyinnovations.com
For additional results, visit (Like) our Facebook page at https://www.facebook.com/hanleyinnovations.

Thanks for reading.