SonicBoom10

SonicBoom10 - Sonic Boom Anastasios Lyrintzis Purdue...

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Sonic Boom Anastasios Lyrintzis Purdue University School of Aeronautics and Astronautics
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Overview Part 1: Analysis Tools Witham’s F-function (Analytical) Computational Analysis Part 2: Suppression Methodologies Vehicle Shaping Phantom Body Shaping Breakthrough Technologies
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Part 1: Analysis Tools The Sonic Boom, Analysis, and Prediction Tools
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The Sonic Boom October 14, 1947 Chuck Yeager breaks the sound barrier Boom prediction/minimization comes to the forefront of research Boom Basics Multiple shocks form off of many portions of the vehicle Non-linear atmospheric effects tend to coalesce (and attenuate) the waves This non-linear effect produces an ‘N-wave’ signature at the ground level
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The Quasi-Linear Analysis Linear Theory Well known analysis: a a a a + + + = 2 2 1 0 δ p p p p 0 0 Assumes shock disturbances to propagate along parallel characteristic lines Actual flow field has curved parabolic characteristics Thus large errors occur at large distances away from the source (which is a typical flight condition) + + + = + + + = 2 2 1 0 2 2 1 0 ρ δρ u u u u 0 Characteristics Ray-tube Linear Analysis Real Effects
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The Quasi-Linear Analysis Witham’s Approach Rather than discard all linearized (simple) relations, Witham &Lighthill used a linearized analysis with some geometric acoustic correctors built in. Restores the δ 2 terms for a higher order of accuracy The Witham F-Function ( ) ( ) = y dt t S y F 1 s Equivalent Area Calculation r Each cut is projected onto a plane normal to the flight path The Pressure Signature (Bernoulli’s Eq) Pressure Signature Shape Resembles the F-function initially As the distance increases characteristics diverge, signature is stretched, and magnitude is attenuated t y 0 2 π ( ) ( ) 2 1 2 2 2 2 0 2 2 1 r y F M v u u M p p β γ = + + = 1 , 2 = M ( ) ( ) + + = 2 3 2 1 2 1 4 2 1 r y F M r x y r Area due to volume: s Mach plane areas projected onto ‘equivalent axis’ s Begins and ends at zero area r Area due to lift: s Begins at zero, ends at W β /2q dx dl q dx dA l = θ sin 2
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The Quasi-Linear Analysis Modification of the N-wave Maximum overpressure, rise time, and total length of the shock has a major impact on the perceived noise level By modifying the equivalent area (geometry) of the vehicle for given flight conditions, adjustment of these parameters can be accomplished Seebass performed an analytical analysis of Witham’s F-function in order to determine what parameters we should adjust
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The Quasi-Linear Analysis Seebass’ Analysis Three Predominant Conclusions Any improvement in the traditional parameters that govern aircraft efficiency will usually result in a reduction of sonic boom overpressure and impulse The most efficient way to minimize overpressure and impulse is to make the
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SonicBoom10 - Sonic Boom Anastasios Lyrintzis Purdue...

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