• 한국추진공학회지
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• 제19권1호
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• pp.9-17
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• 2015

기본 유동 형상은 상대적으로 얇은 중간층이 연료와 공기 사이에 끼어있는 평행 2단 혼합층으로 구성되어 있다. 본 연구는 중간층의 두께 변화에 따른 연소 향상을 수치해석을 통해 조사하였다. 이 경우에, 난류 혼합층에서 열 방출에 의한 효과가 중요하다. 수치해석을 수행하기 위해 완전 보존적인 비정상 2차 시간 정확도의 하부 반복 기법과 2차 총 변화 억제 기법을 k-${\omega}$ 전단응력이동 모델이 결합된 유한체적법과 함께 사용하였다. 다음과 같이 3개의 경우에 대해 해석을 수행하였다. 연료와 공기로 구성된 단일 혼합층, 연료와 공기 사이에 불활성 기체층이 끼어있는 2단 혼합층, 그리고 연료와 공기 사이에 차가운 연료층이 끼어있는 2단 혼합층. 수치해석은 중간 기체층이 1, 2, 4 mm 인 경우에 대하여 수행되었다. 기체층의 총 두께는 4 cm이다. 불활성기체층이 2, 4 mm인 경우와 저온의 연료층이 4 mm인 경우에 단일 혼합층의 경우보다 연소영역이 확대된다.

• 대한기계학회논문집B
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• 제21권9호
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• pp.1095-1104
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• 1997

When a high-speed railway train enters a tunnel, a compression wave is generated ahead of the train and propagates along the tunnel, compressing and accelerating the rest air in front of the wave. At the exit of the tunnel, an impulsive wave is emitted outward toward the surrounding, which causes a positive impulsive noise like a kind of sonic boom produced by a supersonic aircraft. With the advent of high-speed train, such an impulsive noise can be large enough to cause the noise problem, unless some attempts are made to alleviate its pressure levels. For the purpose of the impulsive noise reduction, the present study investigated the effect of a vertical bleed duct on the compression wave propagating into a model tunnel. Numerical results were obtained using a Piecewise Linear Method and testified by experiment of shock tube with an open end. The results showed that the vertical bleed duct reduces the maximum pressure gradient of compression wave front by about 30 percent, compared with the straight tunnel without the bleed duct. As the width of the vertical bleed duct becomes larger, reduction of the impulsive noise is expected to be greater. However the impulsive noise is independent of the height of the vertical bleed duct.

• 대한기계학회논문집B
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• 제21권11호
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• pp.1403-1412
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• 1997

When a high-speed railway train enters a tunnel, a compression wave is generated ahead of the train and propagates through the tunnel, compressing and accelerating the rest air in front of the wave. At the exit of the tunnel, an impulsive wave is emitted outward toward the surrounding, which causes a positive impulsive noise like a kind of sonic boom produced by a supersonic aircraft. With the advent of high-speed train, such an impulsive noise can be large enough to cause the noise problem, unless some attempts are made to alleviate its pressure levels. In the purpose of the impulsive noise reduction, the present study calculated the effect of porous walls on the compression wave propagating into a model tunnel. Two-dimensional unsteady compressible equations were differenced by using a Piecewise Linear Method. Calculation results show that the cavity/porous wall system is very effective for a compression wave with a large nonlinear effect. The porosity of 30% is most effective for the reduction of the maximum pressure gradient of the compression wave front. The present calculation results are in a good agreement with experimental ones obtained previously.