• 제목/요약/키워드: Strong Shock

검색결과 243건 처리시간 0.018초

공동이 있는 수직 분사 초음속 연소기 내의 불안정 연소유동 해석 (Numerical Analysis of Unstable Combustion Flows in Normal Injection Supersonic Combustor with a Cavity)

  • Jeong-Yeol Choi;Vigor Yang
    • 한국추진공학회:학술대회논문집
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    • 한국추진공학회 2003년도 제20회 춘계학술대회 논문집
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    • pp.91-93
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    • 2003
  • A comprehensive numerical study is carried out to investigate for the understanding of the flow evolution and flame development in a supersonic combustor with normal injection of ncumally injecting hydrogen in airsupersonic flows. The formulation treats the complete conservation equations of mass, momentum, energy, and species concentration for a multi-component chemically reacting system. For the numerical simulation of supersonic combustion, multi-species Navier-Stokes equations and detailed chemistry of H2-Air is considered. It also accommodates a finite-rate chemical kinetics mechanism of hydrogen-air combustion GRI-Mech. 2.11[1], which consists of nine species and twenty-five reaction steps. Turbulence closure is achieved by means of a k-two-equation model (2). The governing equations are spatially discretized using a finite-volume approach, and temporally integrated by means of a second-order accurate implicit scheme (3-5).The supersonic combustor consists of a flat channel of 10 cm height and a fuel-injection slit of 0.1 cm width located at 10 cm downstream of the inlet. A cavity of 5 cm height and 20 cm width is installed at 15 cm downstream of the injection slit. A total of 936160 grids are used for the main-combustor flow passage, and 159161 grids for the cavity. The grids are clustered in the flow direction near the fuel injector and cavity, as well as in the vertical direction near the bottom wall. The no-slip and adiabatic conditions are assumed throughout the entire wall boundary. As a specific example, the inflow Mach number is assumed to be 3, and the temperature and pressure are 600 K and 0.1 MPa, respectively. Gaseous hydrogen at a temperature of 151.5 K is injected normal to the wall from a choked injector.A series of calculations were carried out by varying the fuel injection pressure from 0.5 to 1.5MPa. This amounts to changing the fuel mass flow rate or the overall equivalence ratio for different operating regimes. Figure 1 shows the instantaneous temperature fields in the supersonic combustor at four different conditions. The dark blue region represents the hot burned gases. At the fuel injection pressure of 0.5 MPa, the flame is stably anchored, but the flow field exhibits a high-amplitude oscillation. At the fuel injection pressure of 1.0 MPa, the Mach reflection occurs ahead of the injector. The interaction between the incoming air and the injection flow becomes much more complex, and the fuel/air mixing is strongly enhanced. The Mach reflection oscillates and results in a strong fluctuation in the combustor wall pressure. At the fuel injection pressure of 1.5MPa, the flow inside the combustor becomes nearly choked and the Mach reflection is displaced forward. The leading shock wave moves slowly toward the inlet, and eventually causes the combustor-upstart due to the thermal choking. The cavity appears to play a secondary role in driving the flow unsteadiness, in spite of its influence on the fuel/air mixing and flame evolution. Further investigation is necessary on this issue. The present study features detailed resolution of the flow and flame dynamics in the combustor, which was not typically available in most of the previous works. In particular, the oscillatory flow characteristics are captured at a scale sufficient to identify the underlying physical mechanisms. Much of the flow unsteadiness is not related to the cavity, but rather to the intrinsic unsteadiness in the flowfield, as also shown experimentally by Ben-Yakar et al. [6], The interactions between the unsteady flow and flame evolution may cause a large excursion of flow oscillation. The work appears to be the first of its kind in the numerical study of combustion oscillations in a supersonic combustor, although a similar phenomenon was previously reported experimentally. A more comprehensive discussion will be given in the final paper presented at the colloquium.

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중환자 호흡 감염에서 반정량적 Procalcitonin 분석 (Semi-quantitative Procalcitonin Assay in Critically ill Patients with Respiratory infections)

  • 김지연;김철홍;박성훈;이창률;황용일;최정희;신태림;박용범;장승훈;이재영;박상면;김동규;이명구;현인규;정기석
    • Tuberculosis and Respiratory Diseases
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    • 제67권3호
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    • pp.205-211
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    • 2009
  • Background: Serum procalcitonin level has been considered prognostic during sepsis and septic shock. We investigated the significance of procalcitonin in critically ill patients with respiratory infections. Methods: The patients who had radiographically diagnosed diffuse lung infiltrations were enrolled on a prospective basis. Bronchoalveolar lavage (BAL) fluid for the purpose of quantitative cultures (${\geq}10^4$ cfu/mL) was obtained from all patients. Serum procalcitonin levels determined by PCT-Q kit were measured on BAL day and classified as follows; <0.5 ng/mL, 0.5~2.0 ng/mL, 2.0~10.0 ng/mL and >10.0 ng/mL. We analyzed the patient's characteristics according to outcome; favorable or unfavorable, defined as death. Results: Patients from the following categories were included: medical 17 (47.2%), surgical 9 (25%), and burned 10 (27.8%). APACHE II scores on admission to intensive care unit were 11.5${\pm}$6.89 and 11 (30.6%) had unfavorable outcomes. A procalcitonin level ${\geq}$0.5 ng/mL was in 17 (47.2%) of all. On univariate analysis, the frequencies of burn injury, mechanical ventilation, multiple organ failure, and a procalcitonin level ${\geq}$0.5 ng/mL were more often increased in patients with unfavorable outcomes than in those with favorable outcomes (p<.05). Also, a higher procalcitonin range and ventilator-associated pneumonia (VAP) were more closely associated with an unfavorable outcome (p<.05). However in multivariate analysis, a strong predictor of unfavorable outcome was burn injury (p<.05). A procalcitonin level ${\geq}$0.5 ng/mL was more sensitive in predicting VAP than unfavorable outcome. Conclusion: A higher procalcitonin level seems to be associated with VAP, but further study is required to know that procalcitonin would be a prognostic marker in critically ill patients with respiratory infections.

옥동(玉洞) 이서(李漵)의 이(理)·기(氣) 대립적(對立的) 사유(思惟) 양식(樣式)과 그 의미(意味) (Okdong Lee Seo's Li(理)-Qi(氣)Dualism and Its Meaning)

  • 윤재환
    • 동양고전연구
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    • 제49호
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    • pp.187-223
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    • 2012
  • 이 글은 옥동 이서의 문집을 통해 그의 학문세계를 이루는 기본 토대인 옥동의 사유(思惟) 양식(樣式)과 체계(體系)를 살펴보기 위해 기획되었다. 필자가 옥동 이서에게 관심을 가지는 이유는 그가 이전까지 그의 가문 안에서 전해지던 가학(家學)의 전통(傳統)에 강한 자극과 충격을 주는 가학(家學) 변화의 시작점으로 인식되고 있기 때문이다. 옥동 이전까지 그의 가문은 문학으로 성가(聲價)를 얻었던 문한가(文翰家)였다고 생각되는데, 이 가문의 학문 경향이 옥동에 의해 경학(經學) 중심으로 변화되었다고 한다. 특히 옥동은 조선 후기 학계를 대표하는 성호(星湖) 이익(李瀷)의 셋째 형으로, 성호의 학문 형성에 중요한 역할을 담당하였다. 옥동은 성호 학문의 골격을 만들어 주었다고 할 수 있는데, 이 과정에서 문학 중심의 가학 전통을 경학 중심으로 전환시켜 성호에게 전했다고 보인다. 따라서 본 연구는 기본적으로 옥동과 옥동 학문 세계의 근저(根底)를 해명해 내기 위한 작업으로 의미를 지니지만, 보다 큰 의미는 옥동 개인을 넘어 조선 후기 학문적 지표의 하나로 존재하는 성호와 그의 학문 세계를 중심으로 형성된 성호학의 기본 골격을 확인한다는 점에서 찾을 수 있다. 옥동의 문집을 살펴보면 옥동은 유가적(儒家的) 성선설(性善說)에 사유(思惟)의 바탕을 두고 있음을 알 수 있다. 특히 그는 세계를 이(理)와 기(氣)의 대립으로 바라보는 이기이원론적(理氣二元論的) 사유체계를 지니고 있었다. 그가 이(理)와 기(氣)를 대립 관계로 바라보았던 것은 순선(純善)하지 못한 인간의 심(心)을 이해하고 해명하기 위해서였다. 옥동은 인간이 인간답기 위해서는 도덕적 완전성을 회복하여야 하고 이를 위해서 "성(誠)과 경(敬)을 통한 심(心)의 수양"을 추구하여야 한다고 보았다. 이와 같은 수양을 통해 유가적(儒家的) 고도(古道)가 구현된 효제(孝悌) 충신(忠信)의 이상 사회를 건설하고 순선(純善)한 인간을 회복하는 것이 옥동의 목표였다. 여기에 옥동의 사유(思惟) 양식(樣式)이 지니는 기본적인 의미가 놓여 있다.