GATE XE (Engineering Sciences) 2025 - Question 31

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Section: Fluid Mechanics | Marks: 2

Figure shows two parallel plates (upper plate at π‘₯= 𝑏 and lower one at π‘₯= βˆ’π‘) of length L (aligned in 𝑧 direction) and infinite width (in 𝑦 direction, normal to the plane of the figure). Two immiscible, incompressible liquids are flowing steadily in the 𝑧 direction through the thin passage between the plates under the influence of horizontal pressure gradient (𝑃0 βˆ’π‘ƒπΏ) L ⁄ . During the flow, the passage is always half-filled with denser fluid I (viscosity πœ‡πΌ) at the bottom and rest is occupied by lighter fluid II (viscosity πœ‡πΌπΌ; πœ‡πΌπΌ< πœ‡πΌ). Considering exactly planar interface between the fluids and no instabilities in the flow, the shear stress, 𝜏π‘₯𝑧 is expressed as: 𝜏π‘₯𝑧= (𝑃0 βˆ’π‘ƒπΏ)𝑏 L [(π‘₯ 𝑏) βˆ’1 2 (πœ‡πΌβˆ’πœ‡πΌπΌ πœ‡πΌ+ πœ‡πΌπΌ)] Which one of the following options correctly identifies the location of the point having maximum velocity of the flow?

Figure for question 31, GATE XE (Engineering Sciences) 2025

  • A. Above the interface
  • B. Below the interface
  • C. At the interface
  • D. At the top plate

Answer: A. Above the interface

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