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This was my engineering viva question and I couldn't think of any example, for I am totally convinced that there cannot be drag in a inviscid flow. It also bothers me whether it is possible, a tricky scenario in fluid mechanics or gas dynamics.

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Horseshoe vortex system in three dimension is a very good example for drag in a inviscid flow. See this

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  • $\begingroup$ can you elaborate a bit so that it will give a vague idea before embarking on the new clue $\endgroup$ – user29561 Sep 13 '13 at 15:19
  • $\begingroup$ what about the pressure drag generated by any asymmetric object? like an airfoil.. Although the pressure drag for inviscid flow is low, it is still present. $\endgroup$ – aditya kp Sep 13 '13 at 15:29
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    $\begingroup$ but is the "term" pressure drag correct? for such a case. bcos it is usually used to represent the drag due to the presence of wake behind the body , which(the wake) is present in a viscid flow $\endgroup$ – user29561 Sep 13 '13 at 17:37
  • $\begingroup$ Yes, the term pressure drag is correct, @user29561. An explanation: the resultant force produced by the pressure distribution on the airfoil, when resolved into components parallel and perpendicular to the freestream velocity, the one parallel to the freestream contributes to the drag. and since this is a component of the resultant pressure, it is called the pressure drag. Although, I stress again that, for airfoils, pressure drag in inviscid cases turns out to be zero. $\endgroup$ – aditya kp Sep 14 '13 at 11:31
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Unsteady inviscid flow can have drag. For example, an accelerating flat-plate at an angle of attack experiences a force parallel to it's motion. Same for an oscillating cylinder. See Principles of Ideal-Fluid Aerodynamics by Karamcheti for more details.

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  • $\begingroup$ it will more fruitful if u explain with a few words the "unsteady inviscid flow" that has drag and then provide references to dig deep. $\endgroup$ – user29561 Sep 22 '13 at 12:46
  • $\begingroup$ @user29561 I thought that was exactly what I did. $\endgroup$ – OSE Sep 24 '13 at 15:00

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