Method of fluid flow visualization

A method of flow visualization comprises the steps of coating the surface of a component in a pigmented oil-based paint of non-gelling characteristics, applying dry dye particles, which are soluble in the oil based paint to the surface of the coating and passing a fluid flow over the component. The fluid flow causes the dye particles to translate across the coating so that regions of the particles that are in contact with the coating dissolve to leave trails on the surface of the coating which are indicative of the relative strengths of the fluid flows acting on the surfaces of the component.

This invention relates to a method for the visualization of fluid flows 
over the surfaces of solid components. 
It is known to apply a coating, with non-geling characteristics, to a 
surface of a component which on the subsequent passage of a fluid flow 
thereover will move to produce a visible pattern of streaks in the coated 
surface. The pattern generated in th coating enables visualization of the 
fluid flow direction across the component surfaces. 
In German Patent No. 2659693, a component surface is coated with a wet 
solution of Manganese chloride (Mncl.sub.2) and Hydrogen Peroxide (H.sub.2 
O.sub.2). Ammonia (NH.sub.3) or methylamine is introduced into an 
airstream and passed over the surface. Due to local diffusion and 
absorption effects, colourisation reactions occur on the coated surface of 
the component to give an immediate visual indication of the fluid flow 
over the component surface by way of the varying colour intensity. 
Disadvantages of this known method of flow visualization are that: 
(a) a gas has to be introduced into the airstream at a controlled rate to 
ensure that its concentration is uniform throughout the airstream, 
(b) the introduction of a gas into the airstream may limit the applications 
of this technique and possibly adversely affect the environment in which 
the test is to be conducted, 
(c) the method is indicated by a positive result of colourisation and 
therefore failure to introduce the ammonia leads to lack of colourisation 
effects which unless monitored will be interpreted as a lack of fluid flow 
distribution about certain features. 
The present invention seeks to provide an improved method of fluid flow 
visualization over the surfaces of solid components. 
According to the present invention a method of fluid flow visualization 
comprises the steps of coating a component with a pigmented oil based 
paint of non-geling characteristics, applying dry dye particles which are 
soluble in the oil based paint to the surface of the coating and passing a 
fluid flow over the component, whereby the fluid flow causes the dye 
particles to translate across the coating dissolving to leave trails on 
the surface of the coating which trails enables visualization of the 
passage of the fluid flow over the surface of the component. 
Preferably the pigmented oil based paint, comprises a solid solution of a 
fluorescent pigment in a melamine formaldehyde sulphonamide resin 
suspended in a mineral oil. 
The pigmented oil based paint preferably includes a wetting agent such as 
Linoleic Acid. 
The dry dye particles applied to the coating of pigmented oil based paint 
are preferably of a contrasting phthalocyanine dye.

The invention will now be described by way of example and with reference to 
the accompanying drawing. 
Referring to the drawing a surface 15 of a solid component 17 is coated 
with a pigmented oil based paint 18 of non-geling characteristics, and 
with a viscosity chosen such that the paint coating will not move under 
gravity. 
The following formulation attains a pigmented oil based paint of non-geling 
characteristics and with the necessary viscosity: 120 grammes of a solid 
solution of a fluorescent pigment in a melamine formaldehyde sulphonamide 
resin mixed with 234 grammes of a mineral oil. 
The preferred pigment is produced by Sterling Industrial colours Limited 
and is marketed under the trade name Flare 610 series (Yellow 7). 
The mineral oil, is that marketed under the trade name of Mobil Jet II Oil. 
Optionally 10 grammes of a wetting agent such as Linolic Acid is introduced 
to ensure cohesion of the pigmented oil based paint to the surface 15 of 
the solid component 17. 
Particles of a dry phthalocyanine dye 19 are then uniformly sprinkled onto 
the coating of the oil based paint 18 using a dry brush or an industrial 
air blower depending on the accessibility of the surfaces under test. 
A flow of air 20 is then passed over the solid component 17 and this causes 
the dye particles 19 to translate across the coating of the oil-based 
paint 18. The dye particles 19 move to new positions, as shown for clarity 
by the single dye particle at 19a, under the influence of the air flow. 
The regions of the dye particles that come into contact with the coating 
of the oil-based paint dissolve in the oil as they are translated to leave 
a trail 22 on the surface of the coating. This results in a reduction in 
the size of the particles, as shown at 19a due to their dissolution. 
Preferably a contrasting phthalocyanine dye is sprinkled onto the coating 
of the oil-based paint so that movement of the particles 19 under the 
influence of an air flow produces a pattern of contrasting trails on the 
surface of the coating which permanently records and highlights the fluid 
flow distribution pattern for visualization. 
Comparison of the relative movements of the dye particles 19, provides an 
indication of the relative strengths of the fluid flows acting on the 
surfaces of the component under test. 
The method of flow visualization described and illustrated herein has the 
advantage that by utilizing phthalocyanine dye which is soluble in the 
oil, the subsequent movement of these particles under the influence of a 
gaseous flow causes trails which highlight and permanently record the 
gaseous flow distribution pattern for visualization. Techniques used 
previously relied on streaks appearing in the actual coating on 
application of an air flow. 
Further advantages are that there is no necessity for the introduction of a 
gas into the air flow with the effect that this method will not adversely 
affect the test environment. It thereby removes the necessity for 
monitoring the gas concentration introduced into the air flow leading to 
reductions in both time and expenditure during testing.