Classical Visualization Methods

Schlieren visualization of the Saab J39 Gripen in STARCS T1500 wind tunnel.

Classical Visualization Methods

Qualitative visualization methods are used to under-stand the behavior of the flow field and can often be of great help in establishing the cause of unexpected readings of forces or pressure distributions for example. Both large scale phenomena like trailing
vortices (smoke) and small scale phenomena (surface methods) like locally separated flow and point of laminar-to-turbulent transition can be studied. For supersonic speeds, Schlieren can be used for visualization of compressibility phenomena.
Schlieren
All our high speed wind tunnels are equipped with high quality windows on both sides of the test section in order to allow for Schlieren imaging. We perform both black and white and color Schlieren. A camera as well as a video can be used for recording.
 
Schlieren pictures are generally used to visualize boundary layers, shock waves, wakes and separated flow regions.
Track Record (examples)

Schlieren visualization at Mach 2.5 in STARCS TVM500 wind tunnel.

Smoke
Smoke is entered into the wind tunnel, in front of the test object or the part of it that want to be studied, to make the air flow visible to the eye.
 
A smoke wand, hand held or attached to some traversing system, is generally used. Smoke can be emitted from only one point that can be arbitrary moved in the wind tunnel or from a "fork", giving a 2D or 3D pattern of smoke trails across the model.
 
Using a sheet laser together with the smoke, cross sections of the smoke trail can be illuminated to give a good picture of the structure of a vortex or even an estimate of the size of a separation bubble for example. 
 
The optical access in STARS low speed tunnels; LT1 and LT5 is excellent thanks to the large windows, which makes it easy to observe and record the visualization.
 

Smoke visualization using smoke wand in STARCS low speed wind tunnel LT1.

 

Smoke visualization on a buss in STARCS low speed wind tunnel LT1.

 
 
Surface Coating Methods
Various methods for visualization of the flow close to the surface of the test object can be used. Areas of separated flow, laminar-to-turbulent flow transition and general visualization of the direction of the flow across the surface of the model can be achieved.
 
 
Examples of Surface Coating Methods
  • Sublimation visualization: A coating applied to the surface evaporating in the wind and leaving dried chalk trails describing the flow field closest to the surface.
  • Oil flow visualization: Like sublimation visualization but not drying.

Sublimation method used in STARCS LT1.

 
Tufts
Tufts are typically suitable for showing large to medium size flow field structures, depending on size of the tufts relative to the model. The easy installation also makes it a useful "quick-and-dirty" tool. Unlike the sublimation methods, tufts stay constantly active and is therefore suitable for wide slow sweeps, studying for example the conditions for stall.
 
Thanks to the easy installation, tufts can also be very illustrative on in-situ testing in moderate speeds. It should be pointed out that alike most of the qualitative visualization methods, the benefit of using tufts rely on whether the observer is capable of understanding the implications of the visualized flow field on the characteristics and performance of the test object.
 
Applications
  • Visualization on wind tunnel model.
  • In-flight testing of subsonic aircraft.
  • Real-life testing of high speed water craft.
  • Engine air intake efficiency.

Tufts visualization in STARCS LT1 wind tunnel.

 

 
STARCS adapts to the needs of the customer. Focus is on solving the problem rather than the task. Please, fill in the form below and we will contact you for further discussion to find a solution to your particular problem.

 

 
 

Related topics

Inlet Aerodynamics

STARCS has a unique capacity of high flow rate air suction which can be used for simulation of air inlet specific phenomena.
 
 

Store Release Simulation

An additional highly agile motorized arm attached to the ordinary model sting pod, allow for sophisticated store release simulation.
 
 

T1500 - Transonic Wind Tunnel

T1500 is suited for transonic testing of air- and spacecraft at speeds up to Mach 1.7.
 
 
LT1 - Low Speed Wind Tunnel
STARCS low speed wind tunnel is a multipurpose aerodynamic wind tunnel, capable of testing not only all sorts of aircraft models but also almost any type of transportation, large buildings and wind turbines.