Contact Information

• C. Brickell
  • R. Kunz

Fluids & Structural Mechanics

• Computational Mechanics
• Fluid Dynamics
• Marine & Physical Acoustics
• Noise Control & Hydroacoustics
• Research Facilities

CM Related Links

• Computational Fluid Dynamics Analysis
• Computational Methods Development
• Advanced Fluid Thermal Modeling
  

Images | Animations (Below)

Multiphase flows range from flows dominated by a single phase where we are interested in disperse, low-volume-fraction elements to flows where the two phases are present in nearly the same relative volumes. Inertial effects may cause the presence of even low volume fraction particles and droplets to have a significant effect on the mean, carrier flow. In other cases, the carried phase acts as a passive scalar, and the mean flow may be computed separately from the carried phase. In cases of large cavities over typical engineered applications, the presence of the cavity has a significant interaction with and effect on the mean flow; motion of both phases must be considered in a fully coupled sense. Tools effective for computing nearly all levels of multiphase flows, from highly disperse trace mass fraction type to fully phase separated large cavities, are employed in the ARL Computational Mechanics Division.

Supercavitating vechicles and projectiles
Multiphase flow activities ongoing here include development and application of CFD tools for the analysis of supercavitating vehicles and projectiles. An example is Figure 1 which shows a photograph of supercavitating ultra-high-speed (1500m/s, M=1.05) projectile along with a CFD simulation of this flow field. Note how the cavity and bowshock are captured. More typical of hydrodynamic cavitating flows are large scale cavities such as pictured in Animation 1. Here the unsteady cavitating flow over a blunt cylinder is captured on high speed film (from a water tunnel test). The corresponding CFD model of that flow is shown in Animation 2. This animation illustrates a turbulent simulation with multiphase flow modeled. Figure 2 is a the pictoral result of unsteady turbulent Detached Eddy Simulation (DES) (Animation 2) of natural cavitation around a blunt cylinder. Statistics (mean and standard deviation) are shown over the flow field. Figure 3 presents time series and statistics from the DES. Figure 4 and Animation 3 illustrate computational results (steady and with full 6DOF motion) of modeled flow around high speed supercavitating vehicles.

Cavitating flow over hydrofoils and turbomachinery
Another area of research at ARL is cavitating flow over hydrofoils and turbomachinery. Figure 5 introduces the concept. Cavitation driven thrust breakdown is illustrated on a research propeller. Figures 6, 7, and 8 show unsteady vaporous cavitating flow over a twisted hydrofoil. Animation 4 contains an animation of the same unsteady result. The twisted foil is based on an experimental device meant to simulate turbomachinery flows in a static, water tunnel environment.

Bubbly Flows and Cavitation Inception - see the Bubbly Flows & Cavitation Inception (BFCI) tab above

Microbubble Drag Reduction
Microbubble drag reduction (MBDR) has been explored experimentally for decades as a possible mechanism for improving marine vehicle performance by reducing hull friction resistance. Members of the Computational Mechanics Division were principal investigators in the recent DARPA Friction Drag Reduction program, where a two-fluid model based CFD approach was developed for MBDR applications.

This effort involved:

1. physical model development
2. validation against:
   • low Reynolds number DNS data
   • high resolution moderate Reynolds number flat plate water tunnel measurements
   • low resolution high Reynolds number flat plate water tunnel measurements
     
3. application to existing destroyer and notional high speed ship concepts.

Figures 9, 10, 11, 12, 13, 14 illustrate these program elements.

Nuclear Reactor Thermal Hydraulics - see the Nuclear Reactor Thermal-Hydraulics (NRTH) tab above

Launch simulations
Figure 15 shows a launch simulation of a rocket from a recessed port in a submarine deck. Animation is shown in Animation 5.

Compressible two-phase flow
Compressible two-phase flow is a modeling area with many applications. An example is the work done with beverage cans (see Figure 16, 17 and Animations 6, 7). A major container manufacturer discovered can integrity issues when drop testing the newest, thinner-walled beverage cans. Computational modeling was done that included the effects of drop height, initial pressure/temperature head space, gas content and cavitation. Cavitation (bubble growth with vaporization) is significant in this type of situation. It is known that cavity collapse induces shock waves resulting in peak pressures (sometimes) greater than those of the initial impact. Computational refinement studies show effect on peak values but not general shape and translation of waves (at least for initial few milliseconds).

The test conditions were modeled as follows:

• Upright drop: 4,6, and 8 inches at 60psig
• Inverted drop: 20 and 42 inches at 90psig

Figure 16 shows a cross section of the computational mesh along with pressure versus time plots for selected locations on the can surface. Animation 6 illustrates graphically the cavity growth and collapse inside the can. Figure 17 and Animation 7 show the pressure, volume fraction and a time history of pressure at a point in the can for a drop test in which the can is inverted.

Biological/Biomedical Flows - see the Biological / Biomedical Flows (BBF) tab above

Images
View Image (165kb)	Figure 1: Supercavitating ultra high speed projectile. Photo (experiment, Hrubes, Experiments in Fluids, vol. 30 pg. 57-64, 2001) and plot colored by density: blue<1kg/m3, red>1000kg/m3.
View Image (70kb)	Figure 2: Natural cavitation around a blunt cylinder:
View Image (57kb)	Figure 5: Time series and statistics from unsteady turbulent (DES) modeling of naturally cavitating flow over a blunt ogive.
View Image (129kb)	Figure 6: High Speed Supercavitating Vehicle. Compressible CFD Result
View Image (157kb)	Figure 7: Cavitating Propellers. Experimentally observed cavity, photograph and computed results for a US Navy research propeller.
View Image (160kb)	Figure 8: Computed unsteady vaporous cavitating flow over a hydrofoil.
View Image (188kb)	Figure 9: Computed unsteady vaporous cavitating flow over a twisted hydrofoil.
View Image (175kb)	Figure 10: Computed unsteady vaporous cavitating flow over a twisted hydrofoil. Convergence verification and evidence of resolved turbulence.
View Image (46kb)	Firgure 11: Pressure probe histories Initial: equilibrium 60 psig. 4", 6", 8" upright drops. Following impact, cavity growth, collapse, and shock obvious
View Image (25kb)	Figure 12: 20" and 42" drop on top end. 90psig beverage. 0.25inch head space (when right-side up).
View Image (71kb)	Figure 13: Rubber cast of an adult human tracheobronchial tree (left) and CFD model (right).
View Image (72kb)	Figure 14: Predicted oxygen concentration at each branch location at a particular inhalation timestep.
View Image (75kb)	Figure 15: Contours of normalized relative helicity.
View Image (84kb)	Figure 16: Composite plot of contours of 16 mm particle deposition in the upper 6 bronchi, and quantitative deposition efficiency predictions across a range of particle sizes.

Animations
View Animation (Flash Player 882kb)	Animation 1: Natural cavitation around a blunt cylinder: Color plots and animations are from CFD. First portion is approximately the same cavitation number, 0.35. In the simulations, the cylinder is colored by pressure (red is high, blue is low). The cavity is illustrated by the grey isosurface of liquid volume fraction (equal to 0.5).
View Animation (Flash Player 913kb)	Animation 2: High Speed Supercavitating Vehicles: 3 Views of a Coupled 6DOF/Flow Computation
View Animation (Flash Player 1mb)	Animation 3: Computed unsteady vaporous cavitating flow over a twisted hydrofoil.
View Animation (Flash Player 1.9mb)	Animation 4: Natural cavitation around a blunt cylinder: From water tunnel experiments
View Animation (Animated GIF 3mb)	Animation 5: Upright drop 60psig beverage 0.25" head space. Note cavity growth/collapse in a field Note shock in p field
View Animation (Animated GIF 3.4mb)	Animation 6: 20" and 42" drop on top end. 90psig beverage. 0.25inch head space (when right-side up). 1.5 ms animation