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FINAL LECTURE of NEW MATERIAL!!!

FINAL LECTURE of NEW MATERIAL!!!. (1) How to build a better model (2) Lift, Drag, Pressure forces considered together. Simulitude, dimensional analysis, modelling. Similitude The theory and art of predicting prototype performance from model observations

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FINAL LECTURE of NEW MATERIAL!!!

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  1. FINAL LECTURE of NEW MATERIAL!!! (1) How to build a better model (2) Lift, Drag, Pressure forces considered together

  2. Simulitude, dimensional analysis, modelling • Similitude • The theory and art of predicting prototype performance from model observations • Part of this art and theory involves building a good model • Tip: • It helps if the important dimensionless #’s are the same for the models and the prototype

  3. Some types of simultude • Geometric • Involves dimensionless variables created using length scales • e.g. ( L / W ) = ( LM / WM ) • Sometimes a “model scale” is specified • Scale of 1:10 usually means LM / L = 1 / 10 (for any length) • Dynamic • Involves dimensionless variables of force scales • E.g. Inertial and viscous scales are both important: (Finertial / Fviscous) = (Finertial, M / Fviscous, M) • How do you find the appropriate dimensionless numbers • Intuition • What seems to be important? • Use associated dimensionless numbers • Dimensional analysis • provides important dimensionless numbers

  4. Common dimensionless numbers (in fluid dynamics. See section 8.5) • Reynolds number • Inertial / viscous force • Mach number • Inertial / compressibility force • Weber number • Inertial / surface tension force • Froude number • Inertial / gravitational force • Pressure coefficient (Euler number) • Pressure / inertial force • Strouhal number • Local / convective force (unsteadiness importanat)

  5. Lift / drag • When an object is submerged in a flowing fluid, the fluid is forced to move around it. • As a result, the object is (usually) subjected to forces perpendicular and parallel to free stream velocity • Drag: • forces parallel to free stream velocity • Lift: • forces perpendicular to free stream velocity • These take the form:

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