Begell House Inc.
Journal of Flow Visualization and Image Processing
JFV
1065-3090
3
2&3
1996
INSTABILITIES ON A JET ISSUING NORMALLY INTO A CROSSFLOW
109-127
10.1615/JFlowVisImageProc.v3.i2-3.10
L.-E.
Brizzi
Laboratoire d’etudes aerodynamiques, UMR 6609 SP2MI, Boulevard Marie et Pierre Curie, Teleport 2 BP 30179 86962, Futuroscope Chasseneuil, France; Université de Poitiers ENSMA, Futuroscope Chasseneuil, France
E.
Foucault
Maître de conférence École Supérieure d'ingénieurs de Poitiers, France
J.-L.
Bousgarbies
Chargé de Recherche CNRS, Laboratoire d'Études Aérodynamiques (UMR 6609), France
Visualizations by light amplification by stimulated emission of radiation (laser) tomographies have allowed the study of the flow resulting from the interaction between a circular jet and a cross boundary layer. This type of flow is dominated by the presence of many complex vortices that come from the recombining of the vorticity created in the injection tube and that create along the chamber floor. Results indicate in particular that the organization of the line of vortices, created on the boundary of the jet, depends on the existence of a focus located near the injection hole. Conditions of appearance of this instability have been specified, then a quantitative study of its main characteristics has been conducted by statistical analysis of video recordings.
LOCAL HEAT TRANSFER COEFFICIENT AND FILM EFFECTIVENESS DISTRIBUTIONS ON A CYLINDRICAL LEADING EDGE MODEL USING A TRANSIENT LIQUID CRYSTAL IMAGE METHOD
129-140
10.1615/JFlowVisImageProc.v3.i2-3.20
Srinath V.
Ekkad
Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC, 27695-7910
Hui
Du
Turbine Heat Transfer Laboratory, Department of Mechanical Engineering, Texas A&M University, College Station, Texas 77843-3123
Je-Chin
Han
Turbine Heat Transfer Laboratory, Department of Mechanical Engineering, Texas A&M University College Sation, TX 77843-3123, USA
A transient liquid crystal technique is presented for measuring detailed heat transfer coefficients and film effectiveness on a cylindrical test model with film cooling. The technique uses a thin liquid crystal coating on the test surface and two similar transients tests. The cylinder, coated with a thin layer of liquid crystals, is heated to a uniform surface temperature and suddenly exposed to a cooler mainstream. The time history of color change at each pixel location is analyzed to obtain the local heat transfer coefficient and film effectiveness. Tests were run at a mainstream Reynolds number based on cylinder diameter of 100,900. The effect of blowing ratio on heat transfer coefficient and film effectiveness was studied for five blowing ratios ranging between 0.2 and 1.2. Two roles of holes at ±15° from stagnation and hole spacing of four-hole diameters apart and angled at 30° and 90° to the surface in the spanwise and streamwise directions were used for coolant ejection. Air was used as coolant. Detailed distributions obtained using the present technique provide a better understanding of the film cooling phenomena on the cylinder surface. The technique provides high resolution and more accurate results compared with classic heat transfer measurement techniques. Some of the results from the present study are compared with results obtained using classic heat transfer measurement methods.
SURFACE HEAT TRANSFER VISUALIZATION ON A MODEL GAS TURBINE BLADE USING A TRANSIENT LIQUID CRYSTAL IMAGE TECHNIQUE
141-152
10.1615/JFlowVisImageProc.v3.i2-3.30
Hui
Du
Turbine Heat Transfer Laboratory, Department of Mechanical Engineering, Texas A&M University, College Station, Texas 77843-3123
Srinath V.
Ekkad
Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC, 27695-7910
Je-Chin
Han
Turbine Heat Transfer Laboratory, Department of Mechanical Engineering, Texas A&M University College Sation, TX 77843-3123, USA
A transient liquid crystal technique has been developed to visualize the convective heat transfer coefficient distributions on a model gas turbine blade. A five-blade linear cascade is installed into a low-speed wind tunnel to simulate the gas turbine blade cascade. A color image processing system is used to measure the color change of the liquid crystal layer coated on the middle test blade at the center of the cascade. Detailed heat transfer coefficient distributions on a turbine blade are presented for the different flow Reynolds numbers. The cascade exit flow Reynolds number of the flow passing the cascade based on the blade chord is varied from 7.1 × 105 to 1.02 × 106. Results are compared with those obtained with the thin-foil thermocouple method under the same conditions. It is found that the transient liquid crystal image technique gives more detailed information than the classic thin-foil thermocouple method. Some findings with this technique, such as separation bubble effect on heat transfer coefficient on the pressure surface of the blade, flow transition location, and high heat transfer coefficients near the trailing edges on both the suction and the pressure surfaces of the blade, are an improvement over the classic method. The detailed information obtained using this technique may significantly influence the cooling design of the gas turbine blade.
A LIGHT-SHEET FLOW VISUALIZATION SYSTEM FOR STUDYING AIR-SEA INTERACTION PROCESSES
153-164
10.1615/JFlowVisImageProc.v3.i2-3.40
Magdalena
Anguelova
Air-Sea Interaction Laboratory, Graduate College of Marine Studies, University of Delaware, Lewes, Delaware 19958
Minzheng
Wo
Air-Sea Interaction Laboratory, Graduate College of Marine Studies, University of Delaware, Lewes, Delaware 19958
Shih
Tang
Air-Sea Interaction Laboratory, Graduate College of Marine Studies, University of Delaware, Lewes, Delaware 19958
Jin
Wu
Institute of Hydraulic and Ocean Engineering, National Cheng Kung University, Tainan, Taiwan, Republic of China
A flow visualization system has been successfully developed and used in our Wind-Wave-Current Research Facility. The system is composed of a light sheet generated by an Nd: YAG pulsed laser and an imaging acquisition. The sheet has an effective width of 0.7 m and a thickness of 1 mm. Images of the illuminated area were captured with a CCD and a film camera. These images are useful in studying air-sea interaction processes, such as wave growth, wave breaking, and spume-drop formation. Other potential uses of this light sheet are also addressed with examples from acquired images.
SLAG ACCUMULATION AND SLOSH MEASUREMENTS WITH REAL-TIME RADIOSCOPY
165-176
10.1615/JFlowVisImageProc.v3.i2-3.50
Robert A.
Frederick, Jr.
Department of Mechanical and Aerospace Engineering, Research Institute, Room E-29, University of Alabama in Huntsville, Huntsville, AL 35899
James A.
Nichols
Sverdrup Technology Inc., Arnold Air Force Base, Tennessee 37389
Jon
Rogerson
Naval Air Warfare Center, China Lake, California 93555
During operation, solid propellant rocket motors containing aluminized propellants often retain significant levels of molten metal inside the combustion chamber. This work determined dynamic slag accumulation characteristics inside the rocket motor. The scope includes the acquisition and analysis of real-time radioscopic data recorded from a 1.12 m-diameter rocket motor during its operation. A 9-MeV X-ray source transmitted 4000 rad/min of radiation through a 0.75 by 1.30-m field of view at the aft end of the motor. Low-light video cameras recorded real-time images. Specialized image processing determined the appearance, volume, and slosh characteristics of the retained slag during motor firing. The slag moved actively in response to the internal flow field and increased in volume at a rate of 3.43 ml/s during motor operation. The material sloshed at low frequencies (less than 2 to 3 Hz). The results indicate a slag density of 1.6 g/cm3 at motor burnout.
LARGE-SCALE STRUCTURE IDENTIFICATION OF A TURBULENT SPOT BY TAKING BLASIUS VELOCITY PROFILE AS REFERENCE
177-191
10.1615/JFlowVisImageProc.v3.i2-3.60
Guang
Hong
School of Mechanical Engineering, University of Technology, Sydney, P. O. Box 123, Broadway, NSW 2007, Australia
This paper addresses the large-scale structure identification of an artificially generated turbulent spot that simulates the spontaneous turbulent intermittency in a Blasius boundary layer. The Blasius velocity profile of the laminar boundary layer was taken as a reference to observe the turbulent spot. This differs from the conventional method that takes the wall as a reference. The structure of the spot was identified with the profile of the velocity perturbation that is the deviation of the ensemble-averaged velocity of the interior spot from the velocity of the unperturbed laminar flow surrounding the spot. The velocity perturbations near the central streamline on a y-t plane are taken as a sample to describe the identification method. The identified large-scale structure of the spot is a spanwise vortex moving downstream (forward) and rolling backward in the laminar boundary layer. The streamwise velocity perturbation of the turbulent spot from the experiments is compared with the horizontal velocity component of a vortex numerically generated by a CFD code in order to verify the number of vortices contained in a turbulent spot. Significance of the large-scale structure of turbulent spots is analyzed. The role of turbulent spots under zero and adverse pressure gradients is discussed briefly.
NUMERICAL VISUALIZATION OF FLAME SPREADING IN SOLID-FUEL RAMJET COMBUSTORS
193-205
10.1615/JFlowVisImageProc.v3.i2-3.70
Tong-Miin
Liou
Department of Power Mechanical Engineering, National Tsing Hua University, Hsinchu, Taiwan 407, ROC
Po-Wen
Hwang
Department of Power Mechanical Engineering, National Tsing Hua University, Hsinchu, Taiwan, R.O.C.
A numerical visualization is performed to study turbulent reacting flows in solid-fuel ramjet (SFRJ) combustors. The time-dependent axisymmetric compressible conservation equations are solved with the Smagorinsky subgrid-scale turbulence model. The combustion process considered is a one-step, irreversible, and infinitely fast chemical reaction. The numerical code uses the finite-volume technique, which involves alternating in time the second-order explicit MacCormack's and modified Godunov's schemes. The temporal evolution of flow structures, temperature distribution, and flame shape are visualized in terms of the instantaneous streamlines, temperature contours, and stoichiometric mixture fraction. In addition, the entrainment of the fluid particles into the coherent vortices and the interaction of fuel and air particles are visualized by the timelines, streaklines, and pathlines. The flame spreading in such an SFRJ combustor is found to be characterized by an opposed flame spread and a concurrent one starting from the instantaneous reattachment zone.
STUDY OF PULSATILE FLOWS IN LATERAL ANEURYSM MODELS ON A STRAIGHT PARENT VESSEL USING PARTICLE TRACKING VELOCIMETRY
207-223
10.1615/JFlowVisImageProc.v3.i2-3.80
Tong-Miin
Liou
Department of Power Mechanical Engineering, National Tsing Hua University, Hsinchu, Taiwan 407, ROC
Chin-Chun
Liao
Department of Power Mechanical Engineering, National Tsing Hua University, Hsinchu, Taiwan 30043, Republic of China
Particle tracking velocimetry (PTV) measurements are presented of transient flow fields in the lateral aneurysm model arising from a straight parent vessel at a 90° angle. The flow considered was pulsatile with a Womersley number of 3.9 and the aneurysm was rigid. The Reynolds number based on the bulk average velocity and diameter of the parent vessel was 600. Four consecutive flow-rate phases were selected to characterize the pulsatile flow fields in the aneurysm sac. It is found that there exist two opposite vortices in the upper half and lower half of the aneurysm sac. The fluids near the dome region, when compared with the main stream in the parent vessel, undergo a phase lag leading to the distribution of wall shear stress along the dome wall at the minimal phase that is larger than that at the other investigated phases. Variations of the velocity distribution, vorticity, and wall shear stress through four consecutive phases are also discussed.
CONTROL OF LASER LIGHT SHEET PROFILES FOR TOMOGRAPHIC FLOW ANALYSIS BY MEANS OF AN ACOUSTO-OPTIC DEFLECTOR
225-235
10.1615/JFlowVisImageProc.v3.i2-3.90
L.
Thiery
Université de Franche-Comté, Institut de Génie Energétique 2, Avenue Jean Moulin 90000 Belfort, France
Jean-Pierre
Prenel
University of Franche Comte/CNRS 6174, Belfort, France
The control of the power density profile and of the thickness of laser light sheets is proposed to increase the efficiency of the tomographic analysis of flows: a fast periodic shift of the sheets allows modification of the standard Gaussian light distribution without power losses. An experimental device using thermoelectric microsensors is used to validate this method.
SECONDARY FLOW PHENOMENA IN A ROTATING RADIAL STRAIGHT SQUARE CHANNEL
237-246
10.1615/JFlowVisImageProc.v3.i2-3.100
K. C.
Cheng
Department of Mechanical Engineering, University of Alberta Edmonton, Canada
Liqiu
Wang
School of Chemical Eng., Dalian University of Technology, Dalian, 116012, P.R. China
Flow visualization results for secondary flow phenomena near the exit of a rotating radial straight square channel are presented to study Coriolis instability phenomena (formation of Coriolis vortices) and early laminar-turbulent transition for developing laminar flow regime with Reynolds numbers Re = 500 and 1500 and rotating speeds n = 20 ∼ 313 rpm. The smoke injection method was used for flow visualization. At lower Reynolds numbers, the channel rotation (Coriolis force) has a destabilizing effect. This is in contrast to the stabilizing effect of centrifugal force in curved channel flow. The flow visualization results are compared with the results of numerical solutions reported in the literature. The practical implications of the visualization study for future theoretical and experimental investigations are pointed out.