**4. General design procedure**

The parameters that need to be defined in order to start the overall design are:


According to the impact on the wind tunnel dimensions and flow quality, Table 1 shows a classification of the design variables divided into two categories: main and secondary design parameters.


**Table 1.** Main and secondary wind tunnel design parameters

Now, following the guidelines given above, such as the convergence angle and the contour line shape of the contraction zone, the test and contraction chamber can be fully defined. In the case when both opening angles, *α* and *β*, are the same, the contraction length, *LC*, is given by the expression:

$$L\_{\llcorner\mathbb{C}} = \frac{\left(\llcorner\mathbb{N}\cdot 1\right)\cdot W\_{\text{TC}}}{2\cdot \tan\left(\alpha\_{\ll}\mid 2\right)}\cdot 1$$

flow of 20 m3

standard product.

*HTC*/(*WTC+ HTC*).

parameters.

**4. General design procedure**

18 Wind Tunnel Designs and Their Diverse Engineering Applications

**•** Maximum operating speed, *VTC*.

/s each. The latter option would reduce the total cost because the fans are a

The parameters that need to be defined in order to start the overall design are:

drawbacks of choosing a higher contraction ratio, explained before).

Maximum operating speed, *VTC* Contraction semi angle, α*C/2*

Test chamber height, *HTC* Diffuser semi angle, α*D/2*

Contraction ratio, *N* Corner 1 expansion ratio, *eC1*

**Table 1.** Main and secondary wind tunnel design parameters

Test chamber width, *WTC* Settling chamber non-dimensional length, *lSC*

Test chamber length, *LTC* Diffuser 1 non-dimensional length, *lD1*

**•** Test chamber dimensions: width, *WTC*, height, *HTC*, and length, *LTC*. These parameters allow to compute the cross-sectional area, STC= *WTC HTC*, and the hydraulic diameter, DTC=2 *WTC*

**•** Contraction ratio, *N*≈5 for low quality flow, and *N*≈9 for high quality flow (considering the

According to the impact on the wind tunnel dimensions and flow quality, Table 1 shows a classification of the design variables divided into two categories: main and secondary design

**Main design parameters Secondary design parameters**

Corner 1 non-dimensional radius, *rC1* Corner 4 non-dimensional radius, *rC4* Diffuser 5 non-dimensional length, *lD5* Corner 3 non-dimensional radius, *rC3* Dimension of the fan matrix*, nW*, *nH*

Power plant non dimensional length, *lPP*

Unitary fan diameter, *DF*

Now, following the guidelines given above, such as the convergence angle and the contour line shape of the contraction zone, the test and contraction chamber can be fully defined. In

Corner 2 expansion ratio, *eC2*

Continuing in the upstream direction, the next part to be designed is the settling chamber. The only variable to be fixed is the length, because the section is identical to the wide section of the contraction. In the case when high quality flow is required, the minimum recommended nondimensional length based on the hydraulic diameter, *lSC*, is 0,60. This results from the necessity to provide extra space for the honeycomb and screens. In all other cases, the non-dimensional length may be 0,50. Therefore, the length of the settling, *LSC*, chamber is given by:

$$L\_{\rm SC} = \sqrt{N} \cdot W\_{\rm TC} \cdot l\_{\rm SC} \cdot l$$

To obtain all the data for the geometric definition of the corner 4 satisfying all the recommen‐ dations given above we only need to fix the non-dimensional radius, *rC4*. Its length, which is the same as its width, is:

$$L\_{\triangleleft 4} = W\_{\triangleleft 4} = \sqrt{N} \cdot W\_{\overline{\rm{TC}}} \cdot \{1 + r\_{\triangleleft 4}\}.$$

Going downstream of the test chamber, we arrive at the diffuser 1. Assuming that both semiopening angles are 3,5°, its non-dimensional length, *lD1*, is the only design parameter. Although it has a direct effect on the wind tunnel overall length, we must be aware that this diffuser together with corner 1 are responsible for more than 50% of the total pressure losses. According to the experience, *lD1*>3 and *lD1*>4 is recommended for low and high contraction ratio wind tunnels respectively. The length of the diffuser 1, *LD*1, and the width in the wide end, *WWD*1, is defined by:

$$\begin{aligned} L \; \_{D1} &= W\_{TC} \cdot l\_{D1} \\\\ W\_{WD1} &= \left[ 1 + 2 \cdot l\_{D1} \cdot \tan \left( \alpha\_{D1} / 2 \right) \right] \cdot W\_{TC} .\end{aligned}$$

With regard to the corner 1, once its section at the entrance is fixed (it is constrained by the exit of diffuser 1), we must define the non-dimensional radius, *rC1*, and the expansion ratio, *eC1*. As a result, the width at the exit, *WEC1,* the overall length, *LC1,* and width, *WC1*, can be calculated using:

$$\begin{array}{l}W\_{EC1} = W\_{WD1} \cdot e\_{C1} \\\\ L \quad\_{C1} = W\_{WD1} \cdot \left(e\_{C1} + r\_{C1}\right) \\\\ W\_{C1} = W\_{WD1} \cdot \left(1 + r\_{C1}\right) .\end{array}$$

Therefore, we can already formulate the overall wind tunnel length, *LWT*, as a function of the test chamber dimensions, the contraction ratio, and other secondary design parameters:

$$L\_{\rm WT} = L\_{\rm TC} + \mathcal{W}\_{\rm TC} \cdot \left[ \frac{\langle \underline{\mathcal{M}} \cdot \mathbf{1} \rangle}{2 \cdot \tan \langle \alpha\_{\rm c} / 2 \rangle} + \sqrt{\mathcal{M}} \cdot l\_{\rm SC} + \sqrt{\mathcal{M}} \cdot \left\{ 1 + r\_{\rm C} \right\} + l\_{\rm D1} + \left[ 1 + 2 \cdot l\_{\rm D1} \cdot \tan \left( \alpha\_{\rm D1} / 2 \right) \right] \cdot \left\{ e\_{\rm C1} + r\_{\rm C1} \right\} \right], \quad \underline{\mathcal{M}} \cdot \underline{\mathcal{M}} = \underline{\mathcal{M}} \cdot \underline{\mathcal{M}} + \underline{\mathcal{M}} \cdot \underline{\mathcal{M}}$$

This quick calculation allows the designer to check whether the available length is sufficient to fit the wind tunnel.

Taking into account all the recommended values for the secondary design parameters, a guess value for the wind tunnel overall length, with a contraction ratio *N*=9 (high quality flow), is given by the formula:

*L WT* = *L TC* + 16 · *WTC*.

In the case when *N*=5 (low quality flow), the formula becomes:

*L WT* = *L TC* + 11,5 · *WTC*.

The designer must be aware that any modification introduced to the secondary design parameters modifies only slightly the factor that multiplies *WTC* in the formulas above. Consequently, if the available space is insufficient, the only solution would be to modify the test chamber dimensions and/or the contraction ratio.

As we have already defined the wind tunnel length using the criterion of adequate flow quality, we can now devote our attention to designing the rest of the circuit, the so-called return circuit. The goal is not to increase its length, intending also to minimize the overall width and keeping the pressure loss as low as possible.

Keeping this in mind, the next step in the design is to make a first guess about the power plant dimensions. Following our design recommendations, a typical value for the total pressure loss coefficient of a low contraction ratio wind tunnel, excluding screens and honeycombs in the settling chamber, is 0,20, with respect to the dynamic pressure in the test chamber. This value is approximately 0,16 for a large contraction ratio wind tunnels. If screens and honeycombs were necessary, those figures could increase by about 20%.

As the power plant is placed more or less in the middle of the return duct, the area of the section will be similar to the mid-section of the contraction. Therefore, taking into account the volumetric flow, the total pressure loss, and the available fans, the decision about the type of fan and the number of them can be taken. Using this approach, the power plant would be defined, at least in the preliminary stage.

We will return now to the example we started before for the power plant section. To improve the understanding of the subject, we are going to present a case study. If the test chamber section was square and *N*=5, the mid-section of the contraction would be 1,67 x 1,67 m2 . This would allow us to place 4 standard fans of 0,800 m diameter each. The maximum reduction in the width size would be obtained by suppressing the diffuser 5, obtaining the wind tunnel platform shown in Figure 9. We have not defined the diffusion semi-angle in diffuser 3, but we checked afterwards that it was smaller than 3,5°. Figure 9 is just a wire scheme of the wind tunnel, made with an Excel spreadsheet, and for this reason the corners have not been rounded and are represented just as boxes.

In the case of a 4:3 ratio rectangular test chamber cross-section, the mid-section of the contrac‐ tion would be 1,869x1,401 m2 and for this reason we could suggest the use of 6 standard fans of 0,630 m diameter, organized in a 3x2 matrix, occupying a section of 1,890x1,260 m2 . Figure 10 shows the wire scheme of this new design. We can check that the diffuser 3 semi-angle is below 3,5° as well.

Figure 9. Non-dimensional scheme of a wind tunnel with square section test chamber and low contraction ratio, N≈5. **Figure 9.** Non-dimensional scheme of a wind tunnel with square section test chamber and low contraction ratio, N≈5.

It is clear that the new design is slightly longer and wider, but it is because of the influence of the test chamber´s width, as shown above. It is clear that the new design is slightly longer and wider, but it is because of the influence of the test chamber´s width, as shown above.

Notice that in both cases corner 3 has the same shape as corner 4. Similarly, the entrance section of diffuser 4 is the same as of the

power plant section, and using a diffuser semi-angle of 3,5º, this item is also well defined. At this stage we have completely defined the wind tunnel centre line, so that we can calculate the length, *LCL*, and width, *WCL*, using: Notice that in both cases corner 3 has the same shape as corner 4. Similarly, the entrance section of diffuser 4 is the same as of the power plant section, and using a diffuser semi-angle of 3,5°, this item is also well defined.

��� � ���� � ����/2� � ��� � ��� � �� � ��� � ���� � ����/2� Inline formula At this stage we have completely defined the wind tunnel centre line, so that we can calculate the length, *LCL*, and width, *WCL*, using:

$$\begin{aligned} \text{PL\\_CL} &= \left\{ L\_{\text{C1}} \cdot \mathcal{W}\_{\text{EC1}}/2 \right\} + L\_{\text{D1}} + L\_{\text{TC}} \star L\_{\text{C}} + L\_{\text{ST}} + \left\{ L\_{\text{C4}} \cdot \mathcal{W}\_{\text{ED5}}/2 \right\} \\\\ \text{W\\_} &= \left\{ \mathcal{W}\_{\text{C4}} \cdot \mathcal{W}\_{\text{EC4}}/2 \right\} + L\_{\text{D5}} + \left\{ \mathcal{W}\_{\text{C3}} \cdot \mathcal{W}\_{\text{ED4}}/2 \right\}. \end{aligned}$$

������� � ��� � ���� ���� � � � �. Inline formula 6.0 The distance between the exit of the corner 1 and the centre of the corner 2, DC1\_CC2, can be calculated through the expression (see Figure 11):

> ‐6.0 ‐5.0 ‐4.0 ‐3.0 ‐2.0 ‐1.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 Test Section Contraction Settling Chamber Diffuser 1 Corner 1 Corner 4 Diffuser 5 Corner 3 Diffuser 4 Power Plant Diffuser 2 Corner 2

Figure 10.Non-dimensional scheme of a wind tunnel with rectangular section test chamber and low contraction ratio, N≈5.

$$D\_{C1\\_CC2} = W\_{CL} \ -W\_{ED1} \left(r\_{C1} + \frac{1}{2}\right).$$

4.0 On the other hand:

. This

This quick calculation allows the designer to check whether the available length is sufficient

Taking into account all the recommended values for the secondary design parameters, a guess value for the wind tunnel overall length, with a contraction ratio *N*=9 (high quality flow), is

The designer must be aware that any modification introduced to the secondary design parameters modifies only slightly the factor that multiplies *WTC* in the formulas above. Consequently, if the available space is insufficient, the only solution would be to modify the

As we have already defined the wind tunnel length using the criterion of adequate flow quality, we can now devote our attention to designing the rest of the circuit, the so-called return circuit. The goal is not to increase its length, intending also to minimize the overall width and keeping

Keeping this in mind, the next step in the design is to make a first guess about the power plant dimensions. Following our design recommendations, a typical value for the total pressure loss coefficient of a low contraction ratio wind tunnel, excluding screens and honeycombs in the settling chamber, is 0,20, with respect to the dynamic pressure in the test chamber. This value is approximately 0,16 for a large contraction ratio wind tunnels. If screens and honeycombs

As the power plant is placed more or less in the middle of the return duct, the area of the section will be similar to the mid-section of the contraction. Therefore, taking into account the volumetric flow, the total pressure loss, and the available fans, the decision about the type of fan and the number of them can be taken. Using this approach, the power plant would be

We will return now to the example we started before for the power plant section. To improve the understanding of the subject, we are going to present a case study. If the test chamber section was square and *N*=5, the mid-section of the contraction would be 1,67 x 1,67 m2

would allow us to place 4 standard fans of 0,800 m diameter each. The maximum reduction in the width size would be obtained by suppressing the diffuser 5, obtaining the wind tunnel platform shown in Figure 9. We have not defined the diffusion semi-angle in diffuser 3, but we checked afterwards that it was smaller than 3,5°. Figure 9 is just a wire scheme of the wind tunnel, made with an Excel spreadsheet, and for this reason the corners have not been rounded

In the case of a 4:3 ratio rectangular test chamber cross-section, the mid-section of the contrac‐ tion would be 1,869x1,401 m2 and for this reason we could suggest the use of 6 standard fans

In the case when *N*=5 (low quality flow), the formula becomes:

test chamber dimensions and/or the contraction ratio.

20 Wind Tunnel Designs and Their Diverse Engineering Applications

were necessary, those figures could increase by about 20%.

to fit the wind tunnel.

given by the formula:

*L WT* = *L TC* + 16 · *WTC*.

*L WT* = *L TC* + 11,5 · *WTC*.

the pressure loss as low as possible.

defined, at least in the preliminary stage.

and are represented just as boxes.

0.0 1.0 2.0 3.0 *DC*1\_*CC*<sup>2</sup> = *L <sup>D</sup>*<sup>2</sup> + (*WC*<sup>2</sup> - *WEC*<sup>2</sup> / 2) *WEC*<sup>2</sup> =*WED*<sup>2</sup> ·*eC*<sup>2</sup> *WC*<sup>2</sup> =*WED*<sup>2</sup> ·(*rC*<sup>2</sup> + *eC*2)

‐1.0

On the other hand:

Diffuser 3

������� � ��� � ���� ���� � �

above.

Diffuser 3

‐1.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0

using:

Figure 9. Non-dimensional scheme of a wind tunnel with square section test chamber and low contraction ratio, N≈5.

power plant section, and using a diffuser semi-angle of 3,5º, this item is also well defined.

‐6.0 ‐5.0 ‐4.0 ‐3.0 ‐2.0 ‐1.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 Test Section Contraction Settling Chamber Diffuser 1 Corner 1 Corner 4 Diffuser 5 Corner 3 Diffuser 4 Power Plant Diffuser 2 Corner 2

��� � ���� � ����/2� � ��� � ��� � �� � ��� � ���� � ����/2� Inline formula

�. Inline formula

��� � ���� � ����/2� � ��� � ���� � ����/2�. Inline formula

�

It is clear that the new design is slightly longer and wider, but it is because of the influence of the test chamber´s width, as shown

Notice that in both cases corner 3 has the same shape as corner 4. Similarly, the entrance section of diffuser 4 is the same as of the

At this stage we have completely defined the wind tunnel centre line, so that we can calculate the length, *LCL*, and width, *WCL*,

Figure 10.Non-dimensional scheme of a wind tunnel with rectangular section test chamber and low contraction ratio, N≈5. On the other hand: **Figure 10.** Non-dimensional scheme of a wind tunnel with rectangular section test chamber and low contraction ra‐ tio, N≈5.

*WED*<sup>2</sup> =*WEC*<sup>1</sup> + 2 · *L <sup>D</sup>*<sup>2</sup> · tan (*αD*<sup>2</sup> / 2).

Manipulating and combining those equations, we obtain:

*<sup>L</sup> <sup>D</sup>*<sup>2</sup> <sup>=</sup> *DC*1\_*CC*<sup>2</sup> - *<sup>W</sup> EC*<sup>1</sup> · (*rC*<sup>2</sup> <sup>+</sup> *eC*<sup>2</sup> / 2) <sup>1</sup> <sup>+</sup> <sup>2</sup> · (*rC*<sup>2</sup> <sup>+</sup> *eC*<sup>2</sup> / 2) · tan (*αD*<sup>2</sup> / 2) .

With this value, by substituting it into the previous expressions, we have all the parameters to design diffusers 2 and 3, and corner 2. Finally, it is necessary to check that the opening angles of diffuser 3 are below the limit. In case when the vertical opening angle, *α*, exceeds the limit, the best option is to increase the diffuser 1 length, if this is possible, because it improves flow quality and reduces pressure loss. If the wind tunnel length is in the limit, another option is to add the diffuser 5 to the original scheme. However, it will increase the overall width. When the limit of the horizontal opening angle, *β*, is exceeded, then the best option is to adjust the values of the expansion ratio in corners 1 and 2, because it will not change the overall dimen‐ sions.

The following case study is a wind tunnel with high contraction ratio, *N*≈9, and square section test chamber. In this case, the approximate area of the power plant section will be 2,000 x 2,000 m2 . In this case we have two compatible options to select the power plant. We can just select a matrix of 4 fans, 1,000 m diameter each. However, if the operating speed is rather high, in order to be able achieve the required pressure increment and the mass flow, we may need to use 1,250 m diameter fans. Figure 12 shows both options. Note that the overall planform is only slightly modified and the only difference is the position where the power plant is placed.

The design of the diffusers 2 and 3, and the corner 2 will be done following the same method as for the previous cases.

**Figure 11.** Scheme with the definition of the variable involving the design of diffuser 2 and 3, and corner 2.

*WED*<sup>2</sup> =*WEC*<sup>1</sup> + 2 · *L <sup>D</sup>*<sup>2</sup> · tan (*αD*<sup>2</sup> / 2).

On the other hand:

Diffuser 3

*<sup>L</sup> <sup>D</sup>*<sup>2</sup> <sup>=</sup> *DC*1\_*CC*<sup>2</sup> - *<sup>W</sup> EC*<sup>1</sup> · (*rC*<sup>2</sup> <sup>+</sup> *eC*<sup>2</sup> / 2) <sup>1</sup> <sup>+</sup> <sup>2</sup> · (*rC*<sup>2</sup> <sup>+</sup> *eC*<sup>2</sup> / 2) · tan (*αD*<sup>2</sup> / 2) .

‐1.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0

above.

Diffuser 3

‐1.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0

using:

Figure 11):

������� � ��� � ���� ���� � �

22 Wind Tunnel Designs and Their Diverse Engineering Applications

as for the previous cases.

sions.

tio, N≈5.

m2

Manipulating and combining those equations, we obtain:

With this value, by substituting it into the previous expressions, we have all the parameters to design diffusers 2 and 3, and corner 2. Finally, it is necessary to check that the opening angles of diffuser 3 are below the limit. In case when the vertical opening angle, *α*, exceeds the limit, the best option is to increase the diffuser 1 length, if this is possible, because it improves flow quality and reduces pressure loss. If the wind tunnel length is in the limit, another option is to add the diffuser 5 to the original scheme. However, it will increase the overall width. When the limit of the horizontal opening angle, *β*, is exceeded, then the best option is to adjust the values of the expansion ratio in corners 1 and 2, because it will not change the overall dimen‐

‐6.0 ‐5.0 ‐4.0 ‐3.0 ‐2.0 ‐1.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 Test Section Contraction Settling Chamber Diffuser 1 Corner 1 Corner 4 Diffuser 5 Corner 3 Diffuser 4 Power Plant Diffuser 2 Corner 2

**Figure 10.** Non-dimensional scheme of a wind tunnel with rectangular section test chamber and low contraction ra‐

Figure 10.Non-dimensional scheme of a wind tunnel with rectangular section test chamber and low contraction ratio, N≈5.

Figure 9. Non-dimensional scheme of a wind tunnel with square section test chamber and low contraction ratio, N≈5.

power plant section, and using a diffuser semi-angle of 3,5º, this item is also well defined.

‐6.0 ‐5.0 ‐4.0 ‐3.0 ‐2.0 ‐1.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 Test Section Contraction Settling Chamber Diffuser 1 Corner 1 Corner 4 Diffuser 5 Corner 3 Diffuser 4 Power Plant Diffuser 2 Corner 2

��� � ���� � ����/2� � ��� � ��� � �� � ��� � ���� � ����/2� Inline formula

�. Inline formula

��� � ���� � ����/2� � ��� � ���� � ����/2�. Inline formula

�

It is clear that the new design is slightly longer and wider, but it is because of the influence of the test chamber´s width, as shown

Notice that in both cases corner 3 has the same shape as corner 4. Similarly, the entrance section of diffuser 4 is the same as of the

At this stage we have completely defined the wind tunnel centre line, so that we can calculate the length, *LCL*, and width, *WCL*,

The distance between the exit of the corner 1 and the centre of the corner 2, *DC1\_CC2*, can be calculated through the expression (see

The following case study is a wind tunnel with high contraction ratio, *N*≈9, and square section test chamber. In this case, the approximate area of the power plant section will be 2,000 x 2,000

The design of the diffusers 2 and 3, and the corner 2 will be done following the same method

. In this case we have two compatible options to select the power plant. We can just select a matrix of 4 fans, 1,000 m diameter each. However, if the operating speed is rather high, in order to be able achieve the required pressure increment and the mass flow, we may need to use 1,250 m diameter fans. Figure 12 shows both options. Note that the overall planform is only slightly modified and the only difference is the position where the power plant is placed.

Figure 12.Non-dimensional scheme of a wind tunnel with square section test chamber and high contraction ratio, N≈9. Two different standard power plant options are presented. **Figure 12.** Non-dimensional scheme of a wind tunnel with square section test chamber and high contraction ratio, N≈9. Two different standard power plant options are presented.

One of the most important points mentioned in this chapter refers to the wind tunnel cost, intending to offer low cost design solutions. Up to now we have mentioned such modifications to the power plant, proposing a multi-fan solution instead of the

The second and most important point is the wind tunnel's construction. The most common wind tunnels, including those with square or rectangular test sections, have rounded return circuits, like in the case of the NLR-LSWT. However, the return circuit of DNW wind tunnel is constructed with octagonal sections. Although the second solution is cheaper, in both cases different parts of the circuit needed to be built in factories far away from the wind tunnel location, resulting in very complicated transportation

Figure 13.Non-dimensional scheme of a wind tunnel with rectangular section test chamber and large contraction ratio, N≈9.

‐7.0 ‐6.0 ‐5.0 ‐4.0 ‐3.0 ‐2.0 ‐1.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 Test Section Contraction Settling Chamber Diffuser 1 Corner 1 Corner 4 Diffuser 5 Corner 3 Diffuser 4 Power Plant

Diffuser 2 Corner 2 Diffuser 3

To reduce the costs, all the walls can be constructed with flat panels, which can be made on site from wood, metal or even concrete, like in the case of ITER's wind tunnel. Figure 14 shows two wind tunnels built with wood panels and aluminium standard profile

Both wind tunnels shown in Figure 14 are open circuit. The one on the left is located in the Technological Centre of the UPM in Getafe (Madrid) and its test chamber section is 1,20·1,00 m. Its main application is mainly research. The right one is located in the Airplane Laboratory of the Aeronautic School of the UPM. Its test chamber section is 0,80·1,20 m, and it is normally used for

**5. Wind tunnel construction** 

traditional special purpose single fan.

operation.

structure.

‐2.0 ‐1.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 **5. Wind tunnel construction** 

#### **5. Wind tunnel construction** ‐7.0 ‐6.0 ‐5.0 ‐4.0 ‐3.0 ‐2.0 ‐1.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 Test Section Contraction Settling Chamber Diffuser <sup>1</sup>

‐2.0 ‐1.0

1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0

operation.

structure.

One of the most important points mentioned in this chapter refers to the wind tunnel cost, intending to offer low cost design solutions. Up to now we have mentioned such modifications to the power plant, proposing a multi-fan solution instead of the traditional special purpose single fan. Figure 12.Non-dimensional scheme of a wind tunnel with square section test chamber and high contraction ratio, N≈9. Two different standard power plant options are presented. Diffuser 3 fan diameter 1.25 fan diameter 1.25 fan diameter 1.25

Corner 1 Corner 4 Diffuser 5 Corner 3 Diffuser 4 Power Plant Diffuser 2 Corner 2

The second and most important point is the wind tunnel's construction. The most common wind tunnels, including those with square or rectangular test sections, have rounded return circuits, like in the case of the NLR-LSWT. However, the return circuit of DNW wind tunnel is constructed with octagonal sections. Although the second solution is cheaper, in both cases different parts of the circuit needed to be built in factories far away from the wind tunnel location, resulting in very complicated transportation operation. One of the most important points mentioned in this chapter refers to the wind tunnel cost, intending to offer low cost design solutions. Up to now we have mentioned such modifications to the power plant, proposing a multi-fan solution instead of the traditional special purpose single fan. The second and most important point is the wind tunnel's construction. The most common wind tunnels, including those with square or rectangular test sections, have rounded return circuits, like in the case of the NLR-LSWT. However, the return circuit of DNW wind tunnel is constructed with octagonal sections. Although the second solution is cheaper, in both cases different parts of

the circuit needed to be built in factories far away from the wind tunnel location, resulting in very complicated transportation

like in the case of ITER's wind tunnel. Figure 14 shows two wind tunnels built with wood panels and aluminium standard profile

Figure 13.Non-dimensional scheme of a wind tunnel with rectangular section test chamber and large contraction ratio, N≈9. To reduce the costs, all the walls can be constructed with flat panels, which can be made on site from wood, metal or even concrete, **Figure 13.** Non-dimensional scheme of a wind tunnel with rectangular section test chamber and large contraction ratio, N≈9.

Both wind tunnels shown in Figure 14 are open circuit. The one on the left is located in the Technological Centre of the UPM in Getafe (Madrid) and its test chamber section is 1,20·1,00 m. Its main application is mainly research. The right one is located in the Airplane Laboratory of the Aeronautic School of the UPM. Its test chamber section is 0,80·1,20 m, and it is normally used for To reduce the costs, all the walls can be constructed with flat panels, which can be made on site from wood, metal or even concrete, like in the case of ITER's wind tunnel. Figure 14 shows two wind tunnels built with wood panels and aluminium standard profile structure.

Both wind tunnels shown in Figure 14 are open circuit. The one on the left is located in the Technological Centre of the UPM in Getafe (Madrid) and its test chamber section is 1,20 x 1,00 m2 . Its main application is mainly research. The right one is located in the Airplane Laboratory of the Aeronautic School of the UPM. Its test chamber section is 0,80 x 1,20 m2 , and it is normally used for teaching purposes, although some research projects and students competitions were done there as well. Despite the fact that these tunnels are open circuit, the construction solutions can be also applied to closed circuit ones.

**Figure 14.** Research and education purpose wind tunnels built with wood panel and standard metallic profiles, with multi-fan power plant.

According to our experience, the manpower cost to build a wind tunnel like those defined in figures 9 to 13 could be 3 man-months for the design and 16 man-months for the construction. With these data, the cost of the complete circuit, excluding power plant, would be about 70.000,00 €. In our opinion, the cost figure is very good, considering the fact that the complete building time possibly may not exceed even 9 months.

Wehavemore reliabledatawithregardtothe ITERwindtunnel,builtin2000-01.Thewhole cost of the wind tunnel, including power plant, work shop and control room, was 150.000,00 €.

This wind tunnel was almost completely built with concrete. Figure 15 shows different stages of the construction, starting from laying the foundations to the almost final view. The small photos show the contraction, with the template used for wall finishing, and the power plant.
