Aerodynamic Nodes and Junctions (Input Forms 6A Through 6H)

SEGMENT A +

SEGMENT B

SEGMENT C

K=0.0 K=0.7

K=0.0 K=0.7

K=0.0 K=0.0 +

Losses at junctions are only permitted to be entered for factors other than changes in area or turns between the segments at the junction. The user could just as easily enter the losses in both the positive and negative directions due to the walkway in the above example at the forward end of

SEGMENT C, or the positive loss at the forward end, positive flow position and the negative loss at the backward end, negative flow position. Similarly, the user could have entered the positive loss at the backward end, positive flow position, and the negative loss at the forward end, negative flow position of SEGMENT C. The orientation of the losses and the convention established when entering losses is entirely up to the user.

4.3 Aerodynamic Nodes and Junctions (Input Forms 6A Through 6H)

As previously stated, a junction is defined as the intersection of two or more sections, or the point where a section exits to the atmosphere (such as at portals and the tops of vent shafts). A node is located at each junction in a system. As explained in the Geometry Section, nodes may be placed in a continuous tunnel section to enable future modifications to the system to be done without large changes in the input data. These nodes are referred to as “dummy” nodes as they serve no purpose but to allow for future modifications to the program. When a “dummy” node is placed in a continuous tunnel section, the continuous tunnel section is divided into two continuous tunnel sections. In addition, a junction is created at the “dummy” node as the two newly created sections intersect at the “dummy” node. Obviously, when a node is added to a system, a junction is created, and vice versa. There are eight different types of

junctions. The junction type depends on the geometry of the system in the vicinity of the node. All possible junction configurations can be described by at least one of these eight junction types. The user must determine which type of junction best applies for each node location in the system. The user enters the junction data in Forms 6A through 6H. A drawing of the various types of system geometry that determines the type of junction is given in Figure 4.9. A description of each junction type is given as follows:

I.

Tunnel

II.

III.

Examples of Three Aerodynamic Type 0 Nodes

“Dummy” Node

Straight-Through Junction

Portal (Tunnel Outlet to Atmosphere) Node

Portal

Tunnel

Node

Vent Shaft Outlet to Atmosphere

Tunnel

4-29 4

Aerodynamic Node Type 1

Tunnel to Tunnel Crossover Junction 1

3

2

3

Aerodynamic Node Type 2

Dividing Wall Termination Junction

NOTE: Refer to page 4-33 for a description of Node Type 7.

Figure 4.9 Junction Configurations (continued) 1

2

Aerodynamic Node Type 3

“T” Junction 1

3

2

Aerodynamic Node Type 4

Angled Junction 1

3 θ

2

Aerodynamic Node Type 5

“Y” Junction 1

θ 3

2 θ Node

Node

Dividing Wall Node

Node

Node

Aerodynamic Type 0 Node: Straight-Through Junction or Portal

The straight-through junction is at the point where a “dummy” node has been placed in a uniform length of tunnel. The dummy node divides the uniform length of tunnel into two different sections with the same physical characteristics. The dummy node creates a “two-branch” junction which is formally referred to as a “straight-through” junction.

There is a node at every opening to the atmosphere in a system. These openings include portals and vent shaft outlets where flow exits to the atmosphere. The portal junction is a “single-branch” junction and includes both portals and vent shaft outlets to the atmosphere. Portal junctions are also aerodynamic type 0 nodes (see Figure 4.9).

The user does not have to provide the geometry of the junction for aerodynamic Type 0 nodes.

The user only has to enter a zero for the aerodynamic node type in Form 6A.

Aerodynamic Type 1 Node: Tunnel to Tunnel Crossover Junction

The tunnel-to-tunnel crossover junction occurs where a large opening in a dividing wall between two adjacent tunnels exists (see Figure 4.9). The data on the geometry of a tunnel-to-tunnel crossover junction is entered in Form 6C.

The tunnel-to-tunnel junction is a “multiple-branched” junction comprising four separate branches.

The user must enter in Form 6C the section identification numbers of the sections that constitute the four branches of the tunnel-to-tunnel crossover junction. In addition, the user must enter the aspect ratio for the junction. The aspect ratio for a tunnel-to-tunnel crossover junction is defined as the ratio of the length of the crossover opening to twice the height of the tunnel (L/2H).

Aerodynamic Type 2 Node: Dividing Wall Termination Junction

The dividing wall termination junction is where a dividing wall between two adjacent tunnels ends and the two tunnels merge into one (see Figure 4.9). The data on the geometry of a dividing wall

termination junction is entered in Form 6D.

The dividing wall termination junction is a multiple-branched junction comprising three separate branches. The user must enter in Form 6D the section identification numbers of the sections that constitute the three branches of the dividing wall termination junction.

Aerodynamic Type 3 Node: “T” Junction

The “T” junction occurs where either a tunnel or a vent shaft branches off at a 90-degree angle from a separate continuous tunnel. The area of the continuous tunnel before the junction must be greater than or equal to the area of the continuous tunnel after the junction (see Figure 4.9). The data on the

4-31 of the junction. In addition, the user must enter the aspect ratio for the junction. The aspect ratio for a “T”

junction is defined as the ratio of the axial length of the vent shaft or tunnel that runs perpendicular to the straight-through tunnel (Branch 3) to the width of this perpendicular branch at the junction (L/W). The aspect ratio for a “T” junction is depicted as follows: