Project SEATTLER for renewable electricity.

Rugescu, Radu Dan ; Tache, Florin ; Chiciudean, Teodor Gelu 等

Abstract: The objective of the research described in this paper was to develop numerical simulations and to compare the results with laboratory experiments in new, promising zones of aeroacoustics, considered fruitful for the environmental technologies, particularly related to aerodynamic noise suppression. When noise measurements are not being conducted, the cold air turbine embedded in the tower can be used as an efficient, eco-friendly source of energy.

Named SEATTLER from Solar Energy Actuator for Tall Tower Low-cost Electricity Research, this moderately tall tower creates a considerable air acceleration and allows the aerodynamic noise to be definitely perceived. Numeric simulations applied on this architecture reveal astonishing air velocities well over 100 m/s in the test chamber area.

Key words: gravitational draught, infra-turbulence wind tunnel, solar energy, cold air turbine

1. Introduction

The destination of the facility here described is to allow the development of numerical simulation activities and laboratory experiments in the new and important field of aeroacoustics, considered fruitful for the environmenta technologies, particularly related to aerodynamic noise suppression. The laboratory will consist of four complementary branches, namely the gravitational draught for aeroacoustics and infra-turbulence aerodynamics (GDA), solar energy heating (SHE), space structures and orbital surveillance for environmental management (SOS) and gravitational oscillator studies (GOS). Each branch accommodates a subsequent number of specific activities.

2. SEATTLER first hits

The SEATTLER S&T objectives are to create an innovative, non-mechanical air accelerator with double application: as an infra-turbulence, zero driving noise acoustic wind tunnel and as a cheap solar radiation, direct action electric power plant.

The first, wind-tunnel application, means that noise of industrial fans and especially of aircraft engines will be ideally studied and means of suppression found, at a yet unattained level due to its zero noise. The second one claims a small area alternative to the SB GmbH Solar Tower power plant that uses a very large greenhouse solar collector. With its reduced area collector and high radiation temperature, the SEATTLER solar energy tower ends in a cheaper and totally ecological manner of electricity production. Regarding the SEATTLER tunnel, the crucial progress is the complete removal of all moving parts and consequently of all driving noise sources.

Named SEATTLER from Solar Energy Actuator for Tall Tower Low-cost Electricity Research, it allows the noise of the flowing air to be definitely perceived. The new tool will address the area of both fundamental and industrial research for noise protection of the environment and especially noise reduction in aeronautics, as desired by the ACARE-2020 project.

[ILLUSTRATIONS OMITTED]

The avenue towards environment-friendly aircraft engines will thus be cleaned. Besides the obvious acoustical quality of the rig, its construction is by far much simpler and far less expensive than of any other existing noise test facility. It has a vertical, small space consuming, lightweight design, to be easily incorporated amidst other or twinned to other existing facilities. It is possible to accommodate it, for example, near the well-known Bremen University Drop Tower (upper photo), or directly side-added to such an existing tall building. A height of the SEATTLER tunnel of 80 meters could attract air speeds of more than 50 m/s in the test chamber. At the base of the vertical exhauster (lower photo), a test chamber building is accommodated.

Neither noise nor vibrations will be sent by SEATTLER to the surroundings, offering in addition a much higher safety-level in operation also. Tinny noise reduction effects will become accessible and new standards in aeroacoustics will emerge, with major benefits for noise investigations on turbo-engine individual parts. Because all existing facilities are propelled by fan type mechanical driving equipment, they inevitably produce the well-known eigen-noise: part from the driving equipment and part from the flow of air in the very tunnel (see Fig. 3).

This behavior highly worsens the investigation and sensible progress could only be made when the eigen-noise of the wind tunnel is either drastically reduced or completely suppressed, as in the case of the SEATTLER solution.

[FIGURE 3 OMITTED]

The current large-scale electrical fans, despite some recently made progress, manifest a residual level of eigen-noise, while SEATTLER will be free of any driving-equipment eigen-noise (see table below).

The examination of the table allows to point out the clear distinction of the SEATTLER solution, where the driving noise is reduced below 10dB, in contrast to all other high quality facilities, where the best achievement of 29dB is offered in Sweden. It is obvious that the SEATTLER aeroacoustics facility is a high quality tool for the in-depth study of noise emission during aerodynamic flows around profiles, especially through blade cascades of air compressors and turbines. The separation of the soft noise of the flow is usually the main difficulty of all existing installations. A wind tunnel with no moving parts, where the airflow runs under gravity draught only, is a crucial advance in this area and this solution is offered by SEATTLER [11].

The high consumption of energy had also found a practical solution with SEATTLER through the involvement of the solar heating. A focusing array of controlled mirrors is used to easy heat the fresh air and produce the draught effect required to accelerate it through the test chamber. When the wind tunnel is not under operation a cold air turbine is imagined to be introduced in the airflow, powered by the draught of the air and producing electricity after driving a coupled generator. This dual capability is reducing costs further and offers an unexpected solution for energy.

3. Gravity draught for air acceleration

The source of the gravitational draught is the ascending effect of lower density volumes of warm gases in contrast with the higher density surrounding air as a result of their different weights, quantitatively described by the famous Archimede's law.

As far as we keep standing in the frames of this effect of gravity the problem remains entirely immobile. The accompanying buoyant force supplies the maximal estimate for the draught effect. However, when the upward motion of the rarefied gas from the inside is considered, the more elaborated dynamic equilibrium must be approached by the rules of gasdynamics, although its roots remain in the realm of crude Archimede's principle.

[FIGURE 4 OMITTED]

The draft in Fig. 4 shows a vertical stack circulated by the warmed air that defuses into the atmosphere after exiting its top opening. It is surrounded by higher density cold air and the effect of gravity must be accounted in computing the different inner and outer pressures that act on stack's walls. For the sake of simplicity, the air density is considered as independent of altitude [11], while obviously different inside and outside.

The aerostatic influence of the gravitation is then given by the gradient equation both inside (inner density [rho]) and (outer density [[rho].sub.0]) outside the tower,

d p / d z = -g [rho], d p / d z = -g [[rho].sub.0]. (1)

The right hand term in these equations is nothing but the slope to the left of the vertical in each pressure diagram from figure 4, meaning the inner pressure in the stack (left, dotted) is decreasing less steeply and remains closer to the vertical than the outer pressure. The dynamic equilibrium is established when, following a series of transforms, the stagnation pressures inside and outside become equal (Fig. 4).

While the air outside the stack is preserved immobile and due to the effect of gravitation its pressure decreases with altitude from [p.sub.ou](0)[equivalent to] [p.sub.0] at the stack's pad to [p.sub.ou](l)- at the tip of the stack "4", the inner air is flowing and, consequently, its pressure [p.sub.in] varies not only by gravitation, but also due to acceleration and braking along the 0-1-2-3-4 cycle.

The air acceleration takes place at tower inlet between 0-1 as governed by the energy compressible equation ([GAMMA] [equivalent to] [kappa] - 1 / [kappa]) with constant density [[rho].sub.0] along,

[p.sub.1] = [p.sub.0] - [GAMMA] / 2 x [[??].sub.2] / [[rho].sub.0] [A.sup.2], (2)

where A is the cross area of the inner channel and [??] the mass flow rate, constant through the entire stack (steady-state assumption). The air is warmed in the heat exchanger/solar receiver between 1-2 with the heat q per kg with dilatation and acceleration of the airflow, accompanied by the "dilatation drag" pressure loss [1]. Considering also A = const for the cross-area of the heating zone and adopting the variable [gamma] for the amount of heating rather then the heat quantity itself,

[gamm] = [[rho].sub.0] - [[rho].sub.2] / [[rho].sub.0] = 1 = [beta], (3)

with a given control value for

[beta] = [[rho].sub.2] / [[rho].sub.0] > 1, (4)

the continuity condition shows that the variation of the speed is simply given by

[c.sub.2] = [c.sub.1] / [beta]. (5)

The impulse equation gives now the value of the pressure loss due to air dilatation,

[p.sub.2/ + [[??].sup.2] / [[rho].sub.2] [A.sup.2] = [p.sub.1] + [[m.sub.2] / [[rho].sub.0] [A.sup.2] - [DELTA][p.sub.R]. (6)

where a possible pressure loss [DELTA][p.sub.R] due to friction into the heat exchanger is considered. Once the dilatation drag is thus perfectly identified, the total pressure loss [DELTA][p.sub.[SIGMA]] from pad's outside up to the exit from the heat exchanger results as depending on the yet unknown mass flow rate [??], as the sum of the inlet acceleration loss (2) and the dilatation loss (6),

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (7)

equivalent to

[p.sub.2] = [p.sub.0] - [[??].sup.2] / [[rho].sub.0] [A.sup.2] x [gamma](2 - [GAMMA]) + [GAMMA] / 2(1 - [gamma]) - [DELTA][p.sub.R]. (8)

The gravitational effect (1) continues to decrease the value of the inner pressure up to the exit rim of the stack, where the inner pressure becomes

[p.sub.3] = [p.sub.2] - g[[rho].sub.2]l [p.sub.0] - [[??].sup.2] / [[rho].sub.0][A.sup.2] x [gamma](2 - [GAMMA]) + [GAMMA] / 2(1 - [gamma]) - [DELTA][p.sub.R] - g[[rho].sub.2]l. (9)

The constant density assumption along the upper stack [[rho].sub.2] = [[rho].sub.3] [[rho].sub.4] was used. Recovery of the static air pressure, previously [6] considered through a compressible process governed by the Bernoulli equation

[p.sub.4.sup.*] = [p.sub.3] + [GAMMA] [[??].sup.2] / 2[[rho].sub.2][A.sup.2]

is here replaced with the Unger condition [5] of an isobaric exit [p.sub.4.sup.*] = [p.sub.3] which, considered into (9) for replacing [p.sub.3], ends in the equilibrium equation

[p.sub.4.sup.*] = [p.sub.0] - [[??].sup.2] / [[rho].sub.2][A.sup.2] x [gamma](2 - [GAMMA]) + [GAMMA] / 2(1 - [gamma]) - [DELTA][p.sub.R] - g[[rho].sub.2]l. (10)

This means that the dynamic equilibrium is re-established when the stagnation pressure from inside the tower equals the one from outside, at the exit level,

[p.sub.4.sup.*] [equivalent to] [p.sub.in](l) = [p.sub.ou](l) [equivalent to] [p.sub.0](0) - g[[rho].sub.0]l. (11)

This equation is the end element that allows determining the equilibrium value of the air mass flow rate passing through the stack. Equaling (10) and (11),

[p.sub.0] - g[[rho].sub.0]l [equivalent to] [p.sub.0] - [[??].sup.2] / [[rho].sub.2][A.sup.2] x [gamma](2 - [GAMMA]) + [GAMMA] / 2(1 - [gamma]) - [DELTA][p.sub.R] - g[[rho].sub.2]l. (12)

Reducing by the quotient g[[rho].sub.0]l the equilibrium equation appears in the form

[DELTA] p(l) / g [[rho].sub.0]l [equivalent to] 1 + [gamma] - [GAMMA] / 1 - [gamma] x [[??].sup.2] / 2g l [[rho].sup.0.sup.2] [A.sup.2] + [DELTA] [p.sub.R](l) / g [[rho].sub.0]l - [[gamma] = 0. (13)

Depending on the construction of the heat exchanger the drag largely varies. For simple, tubular channels the pressure loss due to frictions stands negligible [6], [8], [9] and the reduced mass flow rate (RMF) results from the simple equation

[R.sup.2] [equivalent to] [[??].sup.2 / 2g l [[rho].sup.2] [A.sup.2] = [gamma] x (1 - [gamma] / [gamma](2 - [GAMMA]) + [GAMMA]. (14)

It represents an alternative to the previous solution of Unger in 1988 [5]

[R.sup.2] [gamma](1 - [gamma]) / 1 + [gamma] (15)

or to the one of Rugescu [6]

[R.sup.2] = [gamma](1 - [gamma] / 1 + [gamma] - [GAMMA] (16)

and gives optimistic values in the region of smaller values of heating (Fig. 5).

[FIGURE 5 OMITTED]

The accelerating potential and the expense of heat to perform this acceleration at optimal conditions result from equations (14)-(16). In a practical manner, the velocity [c.sub.2] results in regard to the free-fall velocity (Torricelli) [c.sub.l]. Its upper margin is given by (17) through (14) while the lower margin by (18) through (15),

[c.sub.2H] = [square root of [gamma] x 2gl / (1 - [gamma])[[gamma](2 - [GAMMA]) + [GAMMA]], (17) [c.sub.2L] = [square root of [gamma] x 2gl / 1 - [[gamma].sup.2] (18)

In fact these formulae render identical results for the optimal [gamma] values (Table 2). For a contraction aria ratio of 10 the maximal airflow velocities in the test chamber [c.sub.e] of the aeroacoustic tunnel versus the tower height are given in Table 2.

The value of [c.sub.e] was computed according to the simple, incompressible assumption, which renders a minimal estimate for the air velocity in the contracted area.

Compressibility whatsoever will tend to increase the actual velocity in the test area, while drag losses, especially in the heat exchanger, will decrease that speed. The optimum values for the heating intensity [gamma] are as follows for upper and lower margin respectively:

[[gamma].sub.H opt] = [square root of 7 - 1] / 6 = 0 0.274292, (19) [[gamma].sub.L opt] = [square root of 2] - 1 = 0.414214. (20)

By substituting these optimum values in the corresponding relations for the c2 velocity, one can easily see that

[c.sup.2.sub.2H] [c.sup.2.sub.2L] = g x l. (21)

4. Turbine effects

According to the design in Fig. 2, a turbine is introduced in the SEATTLER facility next to the solar receiver, with the role to extract at least a part of the energy recovered from the sun radiation and transmit it to the electric generator, where it is converted to electricity. The heat from the flowing air is thus transformed into mechanical energy with the payoff of a supplementary air rarefaction and cooling in the turbine. The best energy extraction will take place when the air recovers entirely the ambient temperature before the solar heating, although this desire remains for the moment rather hypothetical.

[FIGURE 6 OMITTED]

For accesible energy extraction, a quotient is introduced. Major differences appear in the theoretical model with the turbine system as compared to the simple gravity draught wind tunnel previously described. The process of air acceleration at tower inlet is governed by the same energy (Bernoulli) incompressible (constant density [[rho].sub.0] through the process) equation as in the previous case,

[p.sub.1] = [p.sub.0] - [[??].sup.2 / 2[[rho].sup.0][A.sup.2]. (22)

The air is heated in the solar receiver with the amount of heat q, into a process with dilatation and acceleration of the airflow, accompanied by the usual pressure loss, called sometimes "dilatation drag" [8]. Considering a constant area cross-section in the heating solar receiver zone of the tube and adopting the variable a for the amount of heating rather then the heat quantity itself,

[gamma] = [[rho].sub.0] - [[rho].sub.2] / [[rho].sub.0] = 1 - [beta], (23) with a given value for [beta] = [T.sub.1] / [T.sub.2], (24)

the continuity condition shows that the variation of the speed is given by [c.sub.2] = [c.sub.1] / [beta] (25) No global impulse conservation appears in the tower in this case, as long as the turbine is a source of impulse extraction from the airflow. Consequently the impulse equation will be written for the heating zone only, where the loss of pressure due to the air dilatation occurs,

[p.sub.2] + [[??].sup.2] / [[rho].sub.2][A.sup.2] = [p.sub.1] + [[??].sup.2] / [[rho].sub.2][A.sup.2] - [DELTA][p.sub.R]. (26)

A possible pressure loss due to friction into the lamellar solar receiver is considered through [DELTA][p.sub.R]. The dilatation drag is thus perfectly identified and the total pressure loss [DELTA][p.sub.[SIGMA]] from outside up to the exit from the solar heater is present in the expression

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (27)

Observing the definition of the rarefaction factor in (23) and using some arrangements, equation (27) gets the simpler form

[p.sub.2] = [p.sub.0] - [[??].sup.2] / [[rho].sub.0][A.sup.2] x [gamma] + 1 / 2(1 - [gamma]) - [DELTA][p.sub.R]. (28)

The thermal transform further into the turbine stator grid is considered as isentropic, where the amount of enthalpy of the warm air is given by

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII].

If the simplifying assumption is accepted that, under this aspect only, the heating progresses at constant pressure, then a far much simpler expression for the enthalpy fall in the stator appears,

[DELTA][h.sub.23] = [omega]q = [omega]c [sup.p][T.sub.2] [gamma]. (29)

To better describe this process a choice between a new rarefaction ratio of densities [[rho].sub.3]/[[rho].sub.2] or the energy quota [omega] must be engaged and the choice is here made for the later. Into the isentropic stator the known variation of thermal parameters occurs,

[T.sub. 3] / [T.sub.2] = 1 [omega][gamma], (30) [p.sub.3] / [p.sub.2] = [(1 - [omega][gamma]).sup.[kappa] / [kappa] - 1], (31) [[rho].sub.3] / [[rho].sub.2] = [(1 - [omega][gamma]).sup.1 / [kappa] - 1]. (32)

The air pressure at stator exit follows from combining (31) and (28) to render

[p.sub.3] = [[p.sub.0] - [[??].sup.2] / [[rho].sub.0][A.sup.2] x [gamma] + 1 / 2(1 - [gamma] - [DELTA][p.sub.R]] [(1 - [omega][gamma]).sup.[kappa] / [kappa] - 1]. (33)

Considering a Zolly-type turbine the rotor wheel is thermally neutral and no variation in pressure, temperature and density appears. The only variation is in the air kinetic energy, when the absolute velocity of the airflow decreases from [c.sub.3] to [c.sub.3] sin [[alpha].sub.1] and this kinetic energy variation is converted to mechanical work outside. Consequently [[rho].sub.4] = [[rho].sub.3], [p.sub.4] = [p.sub.3], [T.sub.4] = [T.sub.3] and

[c.sub.4] = [c.sub.1] / (1 - [gamma])[(1 - [omega][gamma]).sup.1 / [kappa] - 1]. (34)

The air ascent in the tube is only accompanied by the gravity up-draught effect due to its reduced density, although the temperature could drop to the ambient value. We call this quite strange phenomenon the cold-air draught. It is governed by the simple gravity form of Bernoulli's equation of energy,

[p.sub.5] = [p.sub.3] - g[[rho].sub.3]l. (35)

The simplification was assumed again that the air density varies insignificantly during the tower ascent. The value for [p.sub.3] is here the one in (34). At air exit above the tower a sensible braking of the air occurs in compressible conditions, although the air density suffers insignificant variations during this process.

The Bernoulli equation is used to retrieve the stagnation pressure of the escaping air above the tower, under incompressible conditions

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]. (36)

Value for [p.sub.5] from (35) and for the density ratio from (23) and (32) are now used to write the full expression of the stagnation pressure in "6" as

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (37)

It is observed again that up to this point the entire motion into the tower hangs on the value of the mass flow-rate, yet unknown. The mass flow-rate itself will manifest the value that fulfils now the condition of outside pressure equilibrium, or

[p.sub.6.sup.*] = [p.sub.0.] g[[rho].sub.0]l. (38)

This way, the local altitude air pressure of the outside atmosphere equals the stagnation pressure of the escaping airflow from the inner tower. Introducing (37) in (38), after some re-arrangements, the dependence of the global mass flow-rate along the tower, when a turbine is inserted after the heater, is given by the final developed formula:

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (39)

where the notations are again recollected:

[gamma] = [[rho].sub.0] - [[rho].sub.2] / [[rho].sub.0], the dilatation by heating in the heat exchanger;

[omega] = the part of the received solar energy which could be extracted in the turbine;

[DELTA][p.sub.R] = pressure loss into the heater and along the entire tube either.

All other variables are already specified in the previous chapters. It is clearly noticed that by zeroing the turbine effect ([omega] = 0) the formula (39) reduces to the previous form in (13), or by neglecting the friction to (14), which stays as a validity check for the above computations. For different and given values of the efficiency [omega], the variation of the mass flow-rate through the tube depends parabolically of the rarefaction factor [gamma].

4.1. Discussion

Notice must be made that the result in (39) is based on the convention (29). The exact expression of the energy q introduced by solar heating yet does not change this result significantly. Regarding the squared mass flow-rate itself in (39), it is obvious that the right hand term of its expression must be positive to allow for real values of [R.sup.2].

This only happens when the governing terms present the same sign, namely

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (40)

The larger term here is the ratio [p.sub.0] / g[[rho].sub.0]l), which always assumes a negative sign, while not vanishing. The conclusion results that the tower should surpass a minimal height for a real [R.sup.2] and this minimal height were quite huge. Very reduced values of the efficiency [omega] should be permitted for acceptably tall solar towers. This behavior is nevertheless altered by the first factor in (40) which is the denominator of (29) and which may vanish in the usual range of rarefaction values [gamma]. A sort of thermal resonance appears at those points and the turbine tower works properly well.

4.2. Discussion on denominator

The expression from the denominator of the formulae (39) which gave the flow reportedly, it can be canceled (become 0) for the usual values of the dilatation rapport (ratio) gamma and respectively quota part from energy extracted omega. This strange behavior must be explained. The separate denominator in (40) is,

A [equivalent to] {[gamma] + 1)[(1 - [omega][gamma]).sup.[kappa] + 1 / [kappa]] - [GAMMA]} = 0. (41)

The curve of zeros and the zones with opposite signs are:

[FIGURE 7 OMITTED]

It is yet hard to accept that such a self-amplification or pure resonance of the flow can be real and in fact the formulae (39) does not allow, in its actual form, the geometrical scaling of the tunnel and of the turbine. The rigor of computational formulae is out of any discussion, this showing that the previous result outcomes from the hypotheses adopted. Among those, the hypothesis of isobaric heating before the turbine is obviously the most doubtful.

5. Organisation of the research area

The height of the construction is from 20-m to 140-m. Below and around the test chamber situated at floor 1, a multi-purpose building of the laboratory will be installed (Fig. 8,a). The air inlets are located above the ground floor (Fig. 8,b).

[FIGURE 8 OMITTED]

A surface of around 0.8 ha suffices [7] to collect enough solar energy for powering the aeroacoustic wind tunnel at its highest capacity.

Figure 9 shows a 3D model of the tower assembly designed in a CAD application environment. It comprises the tower with the inlet geometry, the laminator, the turbine and the heater.

[FIGURE 9 OMITTED]

6. Numerical simulations

The geometry presented above has been implemented in a commercial CFD application in order to compare the previously mentioned theory and formulae with numerical simulations on the full-scale model of the draught tower.

The grid used for integrating the equations that describe the air flow through the tower is made of 152600 cells, 307519 faces and 154914 nodes. The operating conditions adopted for the simulation are as follows: operating pressure 101325 Pa, operating temperature 300 K, operating density 1.225 kg/[m.sup.3] gravitational acceleration 9.81 m/[s.sup.2]. Though the flow is primarily laminar, the numerical model used was a well-known k-epsilon model for turbulence, which presented the advantage of taking into account full buoyancy effects. And by giving a low turbulence intensity as input data (1%), the numerical model was very close to the real phenomena occuring in the draught tower. The properties adopted for air are: [c.sub.p0] = 1006.43 j/kg/K, [[lambda].sub.0] = 0.0242 w/m/K, [[eta].sub.0] = 1.7894 x [10.sup.-5] kg/m/s. The boundary conditions for the important sections of the tower were adopted as follows: atmospheric pressure of 101325 Pa and 300 K temperature for the area surrounding the inlet, 101000 Pa and 300 K for the exit section at the top of the 80 m tall tower. For the heater: a temperature of 418 K. No heat exchange with the exterior environment was considered (perfectly isolating walls). Results after some 50000 iterations are briefly presented in the figures below.

[FIGURE 11 OMITTED]

7. Conclusions

Numerical simulations performed had shown that the boundary conditions play a major influence upon the results and the numerical problem is mainly related to the correct formulation of those conditions. In most cases however the air acceleration was found in very good agreement to the experimental data.

The experimental set-up was established with minimal size and maximal simplicity, according to the resources of the CNCSIS grant. Two parameters of the airflow were subjected to measurements: the mean speed in the entrance zone of the tunnel and the exiting air temperature. The experiments were only run with the free gravitational draught and electrical heating of the air. The turbine efect was not yet covered during the tests. It was in the intention of the research team to first demonstrate the capacity of free air acceleration and the value of the theoretical predictions. All these aspects were well covered and the further development of the SEATTLER project depends now on the funding available. The present results prove that the concept is established and really promising. The path towards the gravitational energy extraction tool for ecological, renewable electricity is open.

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[17] Energy Information Administration, Office of Coal, Nuclear, Electric and Alternate Fuels, Renewable Energy Annual 1996, U.S. Department of Energy, Washington, DC 20585, April 1997.

[18] Majdalani, J., Van Moorhem, W. K., Improved time-dependent flowfield solution for solid rocket motors, AIAA Journal v. 36 no. 2 (February 1998) p. 241-8.

Authors data: Dr. Sc. Rugescu R.[adu] D.[an] & Eng. MSc student Researcher Tache F.[lorin], Eng. MSc student Slavu B.[ernard], Eng. MSc student Galan V.[iorel], Eng. PhD student Chiciudean T.[eodor] G.[elu], Eng. PhD & MSc stud. Toma A.[dina] C.[ristina], University "POLITEHNICA" of Bucharest, Romania, rugescu@yahoo.com, flotasoft@yahoo.com, slavu_bernard@yahoo.com, teodorgelu@yahoo.com, tomaadinacristina@yahoo.com

This Publication has to be referred as: Rugescu, R.D.; Tache, F.; Chiciudean, T. G.; Toma, A.C.; Slavu, B. & Galan, V. (2006). Project Seattler for Renewable Electricity, Chapter 42 in DAAAM International Scientific Book 2006, B. Katalinic (Ed.), Published by DAAAM International, ISBN 3-901509-47-X, ISSN 1726-9687, Vienna, Austria

DOI: 10.2507/daaam.scibook.2006.42

Table 1. Comparative outlook of some known low noise tunnels

 Speed
 Wind Tunnel Test Section Range
Facility owner Type (m) (Mach No.)

United Acoustic 1.5 Dia. 1 Mach [less than
Technologies or equal to]
USA 0.65

Georgia Inst. Low turbulence 1 x 1 3 - 23 m/s
Tech. USA

NASA Langley Low turbulence 2.25 x 0.9 x 2.25 0.05 - 0.5
R.C. USA

Goldstein Low turbulence 0.5 x 0.5 x 3.0 42 m/s
Research Lab.
UK

Maibara RTRI Low Noise 3 x 2.5 x 8 85 m/s
Japan

Audi Germany Low noise 9 x 15 x 16 83 m/s

TsAGI Russia T-32 1 x 1 x 4 2 - 80 m/s

Royal Institute Low turbulence 0.8 x 1.2 x 7 68 m/s
Sweden

SEATTLER Zero driver [less than or 0 - 140 m/s
Project noise equal to] 0.4

 Turbulence/ Reynolds
 /Eigen- (/mx
Facility owner noise [10.sup.6])

United n.a. 0.16
Technologies
USA

Georgia Inst. 16%/50dB 0.15
Tech. USA

NASA Langley n.a. 0.13-5.
R.C. USA

Goldstein <0.03%/n.a. n.a.
Research Lab.
UK

Maibara RTRI <0.3%/35dB n.a.
Japan

Audi Germany n.a./46dB 2

TsAGI Russia >0.01%/n.a. 0.13-5.3

Royal Institute <0.02%/29dB n.a.
Sweden

SEATTLER 0.01%/<<10 up to 1
Project dB

Table 2. Draught vs. tower height for a contraction ratio 10

l [c.sub.l] [c.sub.1] [c.sub.2] [c.sub.e]
m m/s m/s m/s m/s

7 11.72 4.85 8.28 82.8
14 16.57 6.86 11.72 117.2
30 24.26 10.05 17.15 171.5
70 37.05 15.35 26.20 262.0
140 52.40 21.71 37.05 370.5