validation is very important to check results

One of the most important steps to build a mathematical model simulating real system is model validation.

I presume validation would be extremely important when testing a model, but when we are scale modeling; maybe if we control the dynamic similarity settings, to make sure we have a similar flow field, then we could conclude that if the actual model was verified somehow, the dynamically similar model will also be dynamically verified. But we must make sure to carefully control that full dynamic similarity is held and no extra forces appear on any of model/scaled model.

Dear Abdulqadri, To answer you question, it is important to define “scale modeling”. Often in fluid dynamics or heat transfer problems, the measurements on full scale engines or plants are extremely difficult and costly. For example building a solid rocket engine of 30 m and testing it is so costly that one cannot test more than one or two different options on full scale. Such different options are often tested on a 1/30 scale. The weight of such an engine decresease with the third power of the scale (1/30)^3=1/30000. The costs of these tests also decrease in a similar way. Hence testing a the dynamic forces on a

scale model 1/10 of an aircraft wing costs roughly 1000 times less than a full scale measurement. Engineers know that some aspects of the behaviour is rather insensitive for the scale, within a typical range. Typically in the range from Reynold 1E-4 to 1E-5 based on the global dimensions of the object (car, wing...). There are also trics to avoid spurioua rffects due to the transition from laminar to turbulent bounadary layers. In scale models wall roughness is added to the model at key points to trigger turbulence in the boundary layer. In this way meaningfull model tests on ship models are carried out at a scale 1/30. However the scale model measurements are only one of the many steps in a design of new rockets, aircrafts and ships. They are complemented by numerical calculations and some analytical considerations. Finally one always carries full scale tests. The scale model tests are only there to allow the engineers to consider more solutions before focusing on the test of the fibal design. Hence it is wrong to state that scale models stidies are usually not verified. Furthermore good scientists and engineers do know, that some aspects of design cannot be tested on a scale model. It us a notorious fact that keeping similarity in a natural convection problem is impossible when scaling down the size. For example if you consider the natural convection in a room of 10 m size and you want to scale this down to a model 1/10, you must increase the temperature difference in the model by a factor 1000. For a typical temperature difference of 20 oC at full scale, one would have to use a temperature difference of 2E+4 oC in the model. As natural convection becomes negligible compared to radiation heat transfer and one cannot use similar materials for the walls...such a scaling model experiment is useless.

In concert hall design, scale models are often used and are usefull. However the quality of the sound in a new concert Hall remains a surprise and corrections are applied to the final concert Hall are always applied to improve the sound.

I do hope this provides you with some answers.

Regards

Mico

In short: scale model experiments are one of the multiple steps in a design procedure. The complementary steps provide a validation of the procedure as a whole.

Of course, similarly to numerical calculation validation, there are elementary steps one should carry. This would be calibrating your instruments before using them in a scale model experiment. Such steps are often reported in good publication, by indicating the accuracy of the meaurenents (reproducibility, absolute accuracy...).