Finally, the approximate expression for the change in flow speed across a weak shock, Equation ( 15. That is, the flow upstream of a given Mach line is not affected by any downstream modifications in the Third, the limited upstream influence is preserved. Thus, on each Mach line, both the flow inclination and the Mach number areĬonstant. Second, each segment of uniform flow becomes vanishingly narrow,Īnd eventually coincides with a Mach line. Positions being straight Mach lines emanating from the wall. First, the shocks become vanishingly weak, their limiting We can also deduce the following results. For any compression shock, there is a corresponding expansion shock. In this case, the net increase in specific entropy becomes vanishingly small. , the smooth turn of Figure 15.6(c) is obtained. In fact, the reduction is by a factor of order The net specific entropy increase can be reduced very significantly, compared to that generated by a single shock is more dense than air and thus has more inertia, causing the bunching up of sound. These compressions and rarefactions result because sound. Hence, if the compression is achieved by means of A sound wave is a pressure wave regions of high (compressions) and low pressure (rarefactions) are established as the result of the vibrations of the sound source. Shall make use of the approximate expressions for weak shocks obtained in the preceding To compare the compression in the two cases, (a) and (b), of Figure 15.6, we This property of limited upstream influence exists as long as the deflection does not become so large that the flow In other words, the flow pattern can be constructed step by step, proceeding downstream. In this region, each segment of the flow is Airways will also become smaller as radial traction of the parenchyma also declines with lung volume. ![]() However, for the present, we shall onlyĬonsider the flow close to the wall. Flow is declining during this phase of expiration due to the forceful expiration causing airway compression and thereby increasing airway resistance. Intersect one another, because they are convergent. These shocks divide the flowįield close to the wall into segments of uniform flow. The wall deflection can be subdivided into several segments, which makeĬompression then occurs through successive oblique shocks. Turn it through an oblique shock, by deflecting the wall through an angle A simple method for compressing a supersonic flow is to Next: Supersonic Expansion by Turning Up: Two-Dimensional Compressible Inviscid Flow Previous: Weak Oblique ShocksĪ shock front increases the pressure and density of the fluid that passes through it.
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