Air flow analysis

AIR/W simulates groundwater-air interaction problems within porous materials such as soil and rock. Its enables analyses ranging from simple single phase air-transfer analyses to complex coupled air-water systems.

The true power of AIR/W is unlocked when it is coupled with TEMP/W to model forced-convection heat flow and density-dependent air flow. This type of analysis is important for studying mine closure, acid rock drainage, or gas transfer.

Key Features

Density Dependent Air Flow

AIR/W can be integrated with TEMP/W to model air transfer via free convection. Density-driven air transfer is generally the dominant mechanism present in systems subjected to climatic influences such as seasonal ground temperature variations.


Estimate Material Properties

The air conductivity function can be generated based on the dry-soil air conductivity and a user-selected volumetric water content function. The estimation process requires only fundamental information for the soil, namely, the dry-soil air conductivity. 


Forced-Convection Heat Transfer

Combine AIR/W with TEMP/W to model forced-convection heat transfer. This process often governs the thermal regime in coarse-grain materials such as waste rock piles, rip-rap on the face of hydraulic structures and embankments with fine-coarse layering.


Single / Dual Phase Flow

Air transfer analysis can be conducted using a single phase material model where only pressure and gravity-driven air flow is considered. A dual phase material model may also be used by coupling air flow to a water transfer analysis.

AIR/W can model almost problem involving air transfer through porous media

Download GeoStudio to view GSZ files

Convective Air Flow

TEMP/W can model convective cells of air movement driven by temperature gradients. It computes air temperatures in a closed box based on thermally-dependent density-driven air flow. Inside a closed volume, this results in circular air movement. Processes are coupled and solved simultaneously. Together, SEEP/W and AIR/W solve for air flow, air pressure and density, while TEMP/W computes convective heat transfer associated with the air flow.


Passive Cooling

Goering (2000) investigated passive cooling within an embankment constructed of unconventional and highly porous material as a means of preserving permafrost. The objective of this example is to simulate similar convective cell behavior in AIR/W and TEMP/W as observed by Goering.


AIR/W's intuitive modeling workflow

Create an AIR/W analysis and set up the problem workspace. Choose analysis type, including steady-state, transient, or coupled (with TEMP/W or CTRAN/W), and define initial pore-water pressure (using SEEP/W) and air flow conditions, convergence criteria, time duration and increments.

Draw the regions in your domain using CAD-like drawing tools, including drawing polygon and circular regions, coordinate import, copy-paste geometric items, length and angle feedback, region splitting and merging, and direct keyboard entry of coordinates, lengths, and angles. Alternatively, import AutoCAD DWG or DXF files directly into GeoStudio to create your domain geometry.

Define the material properties for your analysis, assign them to regions on the domain, and then define your initial pore-water pressure and air flow conditions. Define the air conductivity function, along with the volumetric water content and hydraulic conductivity functions for the SEEP/W analysis. Define the initial seepage and air flow conditions for transient scenarios using results from other SEEP/W or AIR/W analyses or defined spatial functions.

Define air and hydraulic boundary conditions to simulate air pressure, air flow, total head, pressure head and more. Time-varying conditions can also be modeled.

Open Draw Mesh Properties to refine the mesh drawn on the entire domain, or along specific geometric regions, lines or boundaries.

When your problem is completely defined, start the analysis process in the Solve Manager window. The Solve Manager displays the solution progress, allowing you to cancel if necessary. While the solution is in progress, you can look at preliminary results in the Results window.

When the Solver is finished, the total head contours are displayed, with air and water velocity vectors and the phreatic surface shown on the domain. You can display other contours of almost any parameter including pore-water pressure, material properties, water flow, and gradients, using the Draw Contours window. Contour legends and properties can also be modified. Labels can be added to contour lines and flux sections for display in Results View.

Interactively select any node or gauss region to view result information, including pore-air pressure, air flux, air content, material properties, and more. Display plots of computed results over the x- or y-direction or create time-varying plots of results in transient analyses, such as air density, air flux, cumulative air flux, air content, and more. Generate reports of the definition and results, and export into other applications such as Microsoft Excel for further analysis.

The power of integration

AIR/W offers simple but powerful analytical capabilities when used in combination with other GeoStudio products.


Couple AIR/W with SEEP/W

Coupled air-water systems can be modeled with SEEP/W and AIR/W. The two systems are coupled via the matric suction, which is the difference between the pore-air and pore-water pressures. A change to the air pressure will cause a change in the water pressure and vice versa. This type of analysis can be useful for modelling mine closure cover systems or water/air movement in acid generating waste rock.  

TEMP/W results in AIR/W

TEMP/W can use the air fluxes from AIR/W to model forced-convection heat transfer. TEMP/W can also be integrated with AIR/W to model density-dependent air flow.