• Title/Summary/Keyword: transonic flow

Search Result 205, Processing Time 0.023 seconds

Computational analysis of compressibility effects on cavity dynamics in high-speed water-entry

  • Chen, Chen;Sun, Tiezhi;Wei, Yingjie;Wang, Cong
    • International Journal of Naval Architecture and Ocean Engineering
    • /
    • v.11 no.1
    • /
    • pp.495-509
    • /
    • 2019
  • The objective of this study is to analyze the compressibility effects of multiphase cavitating flow during the water-entry process. For this purpose, the water-entry of a projectile at transonic speed is investigated computationally. A temperature-adjusted Tait equation is used to describe the compressibility effects in water, and air and vapor are treated as ideal gases. First, the computational methodology is validated by comparing the simulation results with the experimental measurements of drag coefficient and the theoretical results of cavity shape. Second, based on the computational methodology, the hydrodynamic characteristics of flow are investigated. After analyzing the cavitating flow in compressible and incompressible fluids, the characteristics under compressible conditions are focused upon. The results show that the compressibility effects play a significant role in the development of cavitation and the pressure inside the cavity. More specifically, the drag coefficient and cavity size tend to be larger in the compressible case than those in the incompressible case. Furthermore, the influence of entry velocities on the hydrodynamic characteristics is investigated to provide an insight into the compressibility effects on cavitating flow. The results show that the drag coefficient and the impact pressure vary with the entry velocity, and the prediction formulas for drag coefficient and impact pressure are established respectively in the present study.

Aerodynamic Design Optimization of An Axial Flow Compressor Rotor (반응면 기법을 이용한 천음속 축류압축기의 3차원 형상 최적설계)

  • Ahn, Chan-Sol;Kim, Kwang-Yong
    • 유체기계공업학회:학술대회논문집
    • /
    • 2001.11a
    • /
    • pp.135-142
    • /
    • 2001
  • Design optimization of a transonic compressor rotor (NASA rotor 37) using response surface method and three-dimensional Navier-Stokes analysis has been carried out in this work. Baldwin-Lomax turbulence model was used in the flow analysis. Three design variables were selected to optimize the stacking line of the blade. Data points for response evaluations were selected by D-optimal design, and linear programming method was used for the optimization on the response surface. As a main result of the optimization, adiabatic efficiency was successfully improved. Ana, it is found that the design process provides reliable design of a turbomachinery blade with reasonable computing time.

  • PDF

Evaluation of Efficiency by Applying Different Optimization Method for Axial Compressor (최적화 방법에 따른 축류압축기의 효율평가)

  • Jang, Choon-Man;Abdus, Samad;Kim, Kwang-Yong
    • 유체기계공업학회:학술대회논문집
    • /
    • 2006.08a
    • /
    • pp.543-544
    • /
    • 2006
  • Shape optimization of a transonic axial compressor rotor operating at the design flow condition has been performed using three-dimensional Navier-Stokes analysis and three different surrogate models: i.e.., Response Surface Method(RSM), Kriging Method, and Radial Basis Function(RBF). Three design variables of blade sweep, lean and skew are introduced to optimize the three-dimensional stacking line of the rotor blade. The object function of the shape optimization is selected as an adiabatic efficiency. Throughout the shape optimization of the rotor blade, the adiabatic efficiency is increased for the three different surrogate models. Detailed flow characteristics at the optimal blade shape obtained by different optimization method are drawn and discussed.

  • PDF

Comparison of Turbulence Models in Shock-Wave/ Boundary- Layer Interaction

  • Kim, Sang-Dug;Kwon, Chang-Oh;Song, Dong-Joo
    • Journal of Mechanical Science and Technology
    • /
    • v.18 no.1
    • /
    • pp.153-166
    • /
    • 2004
  • This paper presents a comparative study of a fully coupled, upwind, compressible Navier-Stokes code with three two-equation models and the Baldwin-Lomax algebraic model in predicting transonic/supersonic flow. The k-$\varepsilon$ turbulence model of Abe performed well in predicting the pressure distributions and the velocity profiles near the flow separation over the axisymmetric bump, even though there were some discrepancies with the experimental data in the shear-stress distributions. Additionally, it is noted that this model has y$\^$*/ in damping functions instead of y$\^$+/. The turbulence model of Abe and Wilcox showed better agreements in skin friction coefficient distribution with the experimental data than the other models did for a supersonic compression ramp problem. Wilcox's model seems to be more reliable than the other models in terms of numerical stability. The two-equation models revealed that the redevelopment of the boundary layer was somewhat slow downstream of the reattachment portion.

Flow Visualization of a Commercial Passenger Airplane Realized by Reverse Engineering (역공학으로 구현한 상용 여객기에서 유동 가시화)

  • Kim, Yang-Kyun;Kim, Sung-Cho;Kim, Jeong-Soo;Choi, Jong-Wook;Jin, Hak-Su
    • 한국가시화정보학회:학술대회논문집
    • /
    • 2006.12a
    • /
    • pp.149-152
    • /
    • 2006
  • This paper describes the flow visualization around the model of a commercial passenger airplane, Boeing 747-400, which cruises in the transonic speed. The geometry was realized through the reverse engineering based on the photogrammetry. The three-dimensional inviscid steady compressible governing equations are solved in the unstructured grid system under the cruise condition and in a finite volume method. The convective term is processed by the Crank-Nicholson scheme and first order upwind scheme is applied. The lift and drag forces in the wing with engines increase by 1.49% End 3.9%, respectively compared with the wing without engines.

  • PDF

SHAPING A NOZZLE WITH A CENTRAL BODY (스파이크 노즐 설계)

  • KIM C. W.
    • 한국전산유체공학회:학술대회논문집
    • /
    • 2005.10a
    • /
    • pp.293-298
    • /
    • 2005
  • We calculate the coordinates of an axisymmetric nozzle with a central body. This nozzle ensures a transonic flow with a plane sound surface, which is orthogonal to the symmetry axis and has a wall kink at the sonic point, The Chaplygin transformation in the subsonic part of the flow leads the Dirichlet problem for a system of nonlinear equations. The definition domain of the solution in the velocity-hodograph plane is taken as a rectangle. This enables one to obtain the nozzle with a monotonic distribution of velocity along its subsonic part. In the nonlinear differential equation, the linear Chaplygin operator for plane flows is separated, which allows the iterative calculation of the solution. The supersonic part of the nozzle is calculated under the assumption that the flow at the nozzle exit is uniform and parallel to the symmetry axis; i.e., the supersonic jet outflows to the submerged space with the same pressure. The calculation is performed by the characteristic method. The exact solution of Tricomi equation for near-sonic flows with the straight sonic line is used to 'move away' the sound plane. The velocity distribution alone the supersonic part of the nozzle is also monotonic, which ensures the absence of the boundary-layer separation and, therefore, the adequacy of the ideal-gas model. calculations show that the flow in the supersonic part of the nozzle is continuous (compression shocks are absent)

  • PDF

Incompressible/Compressible Flow Analysis over High-Lift Airfoil Using Two-Equation Turbulence Models (2-방정식 난류모델을 이용한 고양력 익형 주위의 비압축성/압축성 유동장 해석)

  • Kim Chang-Seong;Kim Jong-Am;No O Hyeon
    • 한국전산유체공학회:학술대회논문집
    • /
    • 1998.11a
    • /
    • pp.90-95
    • /
    • 1998
  • The two-dimensional incompressible and compressible Navier-Stokes codes are developed for the computation of the viscous turbulent flow over high-lift airfoils. Incompressible code using pseudo-compressibility and dual-time stepping method involves a conventional upwind differencing scheme for the convective terms and LU-SGS scheme for time integration. Compressible code also adopts an FDS scheme and LU-SGS scheme. Several two-equation turbulence models (the standard $k-{\varepsilon}$ model, the $k-{\omega}$ model. and $k-{\omega}$ SST model) are evaluated by computing the flow over single and multi-element airfoils. The compressible and incompressible codes are validated by computing the flow around the transonic RAE2822 airfoil and the NACA4412 airfoil, respectively. Both the results show a good agreement with experimental surface pressure coefficients and velocity profiles in the boundary layers. Also, the GA(W)-1 single airfoil and the NLR7301 airfoil with a flap are computed using the two-equation turbulence models. The grid systems around two- and three-element airfoil are efficiently generated using Chimera grid scheme, one of the overlapping grid generation methods.

  • PDF

EVALUATION OF TURBULENCE MODELS IN A HIGH PRESSURE TURBINE CASCADE SIMULATION (고압터빈 익렬 주위 유동해석에서 난류모델의 영향 평가)

  • El-Gendi, M.M.;Lee, K.U.;Chung, W.J.;Joh, C.Y.;Son, C.H.
    • Journal of computational fluids engineering
    • /
    • v.17 no.3
    • /
    • pp.53-58
    • /
    • 2012
  • Steady flow simulations through a high pressure turbine guide vanes were carried out. The main objective of the present work is to study the performance of turbulence models on the steady flow prediction from aerodynamic and aerothermal points of view. Three turbulence models were compared, namely SST, k-${\omega}$ and ${\omega}$-Reynolds stress models. The laminar results were also compared. The comparison was done with emphasis on the isentropic Mach number and heat transfer coefficient along the blade, and total pressure loss in the wake region. The calculated isentropic Mach number showed reasonable agreement with experimental data along the blade surface for all three turbulent models. For the total pressure loss in the wake region, ${\omega}$-Reynolds stress model showed the best agreement with the experimental data. However, unless using an appropriate transition model, the heat transfer coefficients of all three turbulent models showed poor agreement with experimental data.

Passive Control of the Condensation Shock Wave Oscillation in a Supersonic Nozzle (초음속 노즐에서 발생하는 응축충격파 진동의 피동제어)

  • Baek, Seung-Cheol;Kwon, Soon-Bum;Kim, Heuy-Dong
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.26 no.7
    • /
    • pp.951-958
    • /
    • 2002
  • Rapid expansion of a moist air or a stream through a supersonic nozzle often leads to non-equilibrium condensation shock wave, causing a considerable energy loss in flow field. Depending on amount of latent heat released due to non-equilibrium condensation, the flow is highly unstable or a periodical oscillation accompanying the condensation shock wave in the nozzle. The unsteadiness of the condensation shock wave is always associated with several kinds of instabilities as well as noise and vibration of flow devices. In the current study, a passive control technique using a porous wall with a plenum cavity underneath is applied for the purpose of alleviation of the condensation shock oscillations in a transonic nozzle. A droplet growth equation is coupled with two-dimensional Navier-Stokes equation system. Computations are carried out using a third-order MUSCL type TVD finite-difference scheme with a second-order fractional time step. An experiment using an indraft wind tunnel is made to validate the present computational results. The results show that the oscillations of the condensation shock wave are completely suppressed by the current passive control method.

Reynolds Number Effects on Aerodynamic Characteristics of Compressor Cascades for High Altitude Long Endurance Aircraft

  • Kodama, Taiki;Watanabe, Toshinori;Himeno, Takehiro;Uzawa, Seiji
    • Proceedings of the Korean Society of Propulsion Engineers Conference
    • /
    • 2008.03a
    • /
    • pp.195-201
    • /
    • 2008
  • In the jet engines on the aircrafts cruising at high altitude over 20 km and subsonic speed, the Reynolds number in terms of the compressor blades becomes very low. In such an operating condition with low Reynolds number, it is widely reported that total pressure loss of the air flow through the compressor cascades increases dramatically due to separation of the boundary layer and the secondary-flow. But the detail of flow mechanisms causes the total pressure loss has not been fully understood yet. In the present study, two series of numerical investigations were conducted to study the effects of Reynolds number on the aerodynamic characteristics of compressor cascades. At first, the incompressible flow fields in the two-dimensional compressor cascade composed of C4 airfoils were numerically simulated with various values of Reynolds number. Compared with the corresponding experimental data, the numerically estimated trend of total pressure loss as a function of Reynolds number showed good agreement with that of experiment. From the visualized numerical results, the thickness of boundary layer and wake were found to increase with the decrease of Reynolds number. Especially at very low Reynolds number, the separation of boundary layer and vortex shedding were observed. The other series, as the preparatory investigation, the flow fields in the transonic compressor, NASA Rotor 37, were simulated under the several conditions, which corresponded to the operation at sea level static and at 10 km of altitude with low density and temperature. It was found that, in the case of operation at high altitude, the separation region on the blade surface became lager, and that the radial and reverse flow around the trailing edge become stronger than those under sea level static condition.

  • PDF