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Q811418 - Effect of a change in Angle of Attack on a normal shock wave

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  • Q811418 - Effect of a change in Angle of Attack on a normal shock wave

    With best intentions, I'd like to refer to the explanation of the question ID 811418 which I think is incorrect, saying there's a secondary tempting answer and giving the incorrect explanation which leads to a confusion. Increasing AoA does increase Mach number over the upper surface which in turn moves the shock wave rearwards as you have explained in many instances, like here for example. The question however, does not say that the AoA is increasing (nor decreasing), it only says there's a change in AoA, while it's left to the answers to define if the AoA increases or decreases. Had the choice B. contained extra words saying: "as AoA increases", that'd be a correct answer as well. I think the explanation is incorrect and it should be updated. Best wishes.
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    What is the impact of a change in Angle of Attack (AoA) on a normal shock wave at a constant Mach number?
    A. The intensity of the shock wave decreases as AoA increases.
    B. The location of the shock wave moves rearwards on the wing. (incorrect tempting answer)
    C. The location of the shock wave moves forwards on the wing.
    D. The intensity of the shock wave increases as AoA increases. (correct answer)

    Explanation:
    Increasing AoA increases the acceleration given to the airflow over the upper surface of the wing, increasing the local Mach number. This will intensify the shock wave.

    Rearwards movement of the shock wave is a tempting answer, as this occurs when free stream Mach number is increasing at constant AoA. But this question is about constant free stream Mach number and increasing AoA.
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