You know the word "draft"? Be concerned about the open window leafs? Wondered why the heating system is not working sufficiently well? Today, these and similar problems can be solved by computer simulation. Let discomfort will only virtual!

SIMULATION OF AIR FLOW IN ROOM WITH VIEW OF AN EXTERNAL FLOW AROUND BUILDINGS

The goal was to study air flow occurring in the office under the following conditions: a) at two distant from each other open windows due to the pressure difference (summer draft), b) at closed windows due to heating of the air batteries (winter).

Modeling draft in the summer

Pressure drop on window leafs was set based on the results of modeling the wind blowing the building and nearby buildings. The computational grid contained regions with different cell size (Fig. 1), the most fine partition is used near the buildings of interest. Arrows in Figure 1 shows location of the window leafs of the room.

Fig. 1. The computational grid used to simulate the external flow around buildings (the arrows indicate location of air vents of the office)

Addressed the various wind directions, and it was found that some of them lead to a pressure differential on either side of the building under consideration (in particular the southern and south-east), while in other areas there is practically no difference. The wind speed was set equal to 7 m/s, which is close to the maximum values for the summer.Figure 2 shows the pressure distribution around buildings, obtained for prevailing in the area wind directions: south (Fig.1a,b) and southeast (Fig.1c,d).

a                                                                        b

c                                                                         d

Fig.2. Pressure distribution around buildings, obtained for the prevailing wind directions: south (a, b) and southeast (c, d) (highlighted in red border, at which wind speed was specified)

As can be seen from the figures 1b and 1d, the pressure difference at the points of the corresponding location of the air vents is on the order of 5 Pa. As shown below, even this small at first glance, the value can create indoor air flow velocities of the order of 3 m/s.

The geometry of space, consisting of two rooms of different sizes within which the calculation was made of heat and mass transfer, and location of air vents are shown in Figure 3.

Fig. 3. The geometry of internal space and the computational grid (window leafs are highlighted in orange)

At the boundaries identified in Figure 3 orange, asked appropriate pressure values obtained by simulating the external flow. Computer simulation has shown air flow at speeds up to 2.5 m/s in the lower areas of the room (Fig.4a).

a                                                                                          b

Fig. 4. The distribution of the velocity field in horizontal sections at a height of 0.22 m (a) and 1.5 m (b)

Modeling of heat and convection currents

The geometry of space in this case coincides with the geometry of the problem, the above described. However, as the boundary conditions were given battery temperature and window openings, shown in Figure 5. Selected values were +70 ° C and +1 ° C for batteries and windows, respectively. Simulation showed the effect of "locking" of heated air flows coming from the battery located in a smaller room (Fig.5b). As a result, there is uneven distribution of temperature in the office, accompanied by greater heat of this room (Fig. 6a). The values of the flow rate is limited to relatively low values (Fig.6b).

a                                                                                               b

Fig. 5. Location batteries and window openings (a) and streamlines (b)

a                                                                                                b

Fig. 6. Temperature distribution (a) and velocity modulus (b) in the office