To analyze the given options regarding the effects of increasing Reynolds number on boundary layer characteristics and transition locations, let's consider the typical behavior in fluid dynamics:
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Boundary Layer Thickness: As the Reynolds number increases, the flow tends to become more turbulent, which generally leads to a thinner boundary layer because the momentum transfer in the outer flow increases.
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Transition Location: The transition from laminar to turbulent flow typically moves forward with increasing Reynolds number. This suggests that the flow becomes turbulent sooner along the surface, which is generally observed in many practical situations.
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Drag: Generally, in the context of flow over a surface, increasing turbulence usually leads to increased drag (especially if we consider drag in terms of skin friction). However, the relationship can be complex, as turbulent flow can also lead to a reduction in pressure drag.
Now let's evaluate the proposed statements:
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"The boundary layer thickness decreases while the transition location moves backwards" - False (boundary layer thickness decreases, but transition location moves forward).
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"The transition location moves forward while the drag increases" - This is generally true. As the flow becomes turbulent further along the surface with increasing Reynolds number, drag increases.
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"The transition location moves forward while the drag decreases" - False (the transition moves forward, but drag generally increases).
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"The boundary layer thickness decreases while the transition location moves forward" - True (boundary layer thickness decreases and transition moves forward with increasing Reynolds number).
Based on this analysis:
- Statement 1 is false.
- Statement 2 is true.
- Statement 3 is false.
- Statement 4 is true.
Therefore, the correct option is: "Both 2 and 4 are true."