5.1. Acoustic measurements

Field measurements of velocity and turbulent quantities have been made much more accessible with the development of acoustic measurement methods. Acoustic Doppler Current Profiler (ADCP), highly efficient and reliable instrument for flow measurements in riverine and open-channel environments, has been used for the first time to determine the velocity profiles in the dam reservoir in Poland.

The measurements are repeated continuously during the movement of the boat. As a result, for a single passage along the cross section, a few hundred to several thousands of partial flow are obtained, which are summed during the measurement process. The measurements are repeated several times. The final result is calculated as the average value of at least four correct runs.

Teledyne RD Instruments' StreamPro Acoustic Doppler Current Profiler (ADCP) was used to validate the hydrodynamic CFD model. The device was mounted on a boat that moves across a transect of the reservoir channel. This technique can be adopted while complying the assumptions: (1) the water surface is not wavy and (2) velocity of the water is less than 2 m/s.

In order to correctly determine the places selected for the verification, the GPS Garmin eTrex 10 has been used. Flow velocity measurements were made in June 2013 and included four cross sections in the Sulejow reservoir and measurements of the flow rate at the inlet to the reservoir of the Pilica and Luciaza rivers.

The places, which have been selected for the verification of the hydrodynamic model, were arranged along the longitudinal axis of the Sulejow reservoir. The selection of these areas was dictated by expecting a different character of flow in indicated areas (Figure 15):


• Tresta (4)—located in the lower part of the artificial lake, where the depth is about 7–8 m. The place is closest to the dam of the reservoir, characterized by, in addition to great depths, the largest cross-sectional width of approximately 2000 m.

## 5.2. Results of model validation

5. Model verification

54 Dam Engineering

5.1. Acoustic measurements

in the dam reservoir in Poland.

of the Pilica and Luciaza rivers.

depth of the basin (approximately 6 m).

runs.

for validation of the numerical simulations.

Numerical simulations have many advantages such as providing results in the entire domain and the ability to make changes to the geometry, boundary, or initial conditions, but numerical models always require validation of the simulations with reliable and appropriate experimental data [22]. The following section describes the measurements for obtaining data necessary

Field measurements of velocity and turbulent quantities have been made much more accessible with the development of acoustic measurement methods. Acoustic Doppler Current Profiler (ADCP), highly efficient and reliable instrument for flow measurements in riverine and open-channel environments, has been used for the first time to determine the velocity profiles

The measurements are repeated continuously during the movement of the boat. As a result, for a single passage along the cross section, a few hundred to several thousands of partial flow are obtained, which are summed during the measurement process. The measurements are repeated several times. The final result is calculated as the average value of at least four correct

Teledyne RD Instruments' StreamPro Acoustic Doppler Current Profiler (ADCP) was used to validate the hydrodynamic CFD model. The device was mounted on a boat that moves across a transect of the reservoir channel. This technique can be adopted while complying the assumptions: (1) the water surface is not wavy and (2) velocity of the water is less than 2 m/s. In order to correctly determine the places selected for the verification, the GPS Garmin eTrex 10 has been used. Flow velocity measurements were made in June 2013 and included four cross sections in the Sulejow reservoir and measurements of the flow rate at the inlet to the reservoir

The places, which have been selected for the verification of the hydrodynamic model, were arranged along the longitudinal axis of the Sulejow reservoir. The selection of these areas was

• Barkowice Mokre (1)—the place closest to the backwaters of the reservoir, located in the riverine zone, characterized by small depths (<3 m) and the highest flow rates.

• Zarzecin (2)—located in the upper, narrow part of the reservoir, with higher flow veloci-

• Bronislawow (3)—situated in the central part of the reservoir, near the former water intake for Lodz City. The place is characterized by a low flow, due to greater width (1500 m) and

ties, resulting in a half-river character. The depth at this point was about 4 m.

dictated by expecting a different character of flow in indicated areas (Figure 15):

A reasonable agreement between the flow pattern predicted by the model and those deduced from the field data was found (Figure 16). To quantify the comparison, relative error was calculated by taking the difference between numerical and measured values and then dividing the results by the measured values. The measured velocity profiles were provided with a relative accuracy within the range 1–10%.

The possible reasons for the discrepancies are (1) inaccuracies in location of measuring points, (2) point velocity measurement errors, (3) errors in modeling the flow, and (4) errors in modeling the geometry.

The first category is related to the field velocity measurements taken from a boat. Considering the fact that a boat cannot maintain an absolute fixed position due to the waving and wind, errors are introduced in velocity measurements. A deviation of 20 cm from the fixed position can cause large errors if there is a steep velocity change in the plane of measurements. The magnitude of this error could not be estimated accurately; however, rough estimate of the nearby velocities within a distance of 20 cm at the measuring point resulted in an error in the range 3–5%.

Figure 15. Hydrological and morphological differentiation of the Sulejow reservoir along the longitudinal axis.

6. Conclusions

Author details

Poland

References

72:4151-4162

Aleksandra Ziemińska-Stolarska

of Fluid Mechanics. 1982;14:153-187

The objective of this study was to develop and validate a three-dimensional numerical model for simulating flow through the long dam reservoir of a complex bathymetry (17 km length). As a result of the study, a three-dimensional one-phase CFD model of flow hydrodynamics in the large water body on the example of the Sulejow reservoir was developed with an accurate

Three-Dimensional CFD Simulations of Hydrodynamics for the Lowland Dam Reservoir

http://dx.doi.org/10.5772/intechopen.80377

57

The results of three-dimensional one-phase CFD model indicate that the flow field in the Sulejow reservoir is transient in nature, with visible swirl flows in the lower part of the lake. The results of simulations confirm the pronounced effect of wind on the water flow in the reservoir and the accumulation of phytoplankton cells in the epilimnion layer of the lacustrine part of the Sulejow reservoir. Methodology developed in the frame of this work can be applied to all types of storage reservoir configurations, characteristics, and hydrodynamic conditions. Results of the simulation are complementary to the direct measurements of the surface water quality. A well-defined and constructed model can be used while developing a strategy for water environment quality control and can be used as an auxiliary tool for the monitoring and

depiction of basin bathymetry and verified on the basis of field measurements.

prediction of surface water quality and decision-making in the field of planning.

Address all correspondence to: aleksandra.zieminska-stolarska@p.lodz.pl

[1] Hutter K. Hydrodynamics of Lakes. NY, USA: Springer-Verlag; 1984

reservoirs. Ecological Engineering. 2000;16(1):181-188

Faculty of Process and Environmental Engineering, Lodz University of Technology, Łódź,

[2] Imberger J, Hamblin PF. Dynamics of lakes, reservoirs and cooling ponds. Annual Review

[3] Serruya S, Hollan E, Bitsch B. Steady winter circulation in lakes constance and kinneret driven by wind and main tributaries. Archiv für Hydrobiologie. 1984;70(1):33-110

[4] Csanady GT. Large-scale motion in the great lakes. Journal of Geophysical Research. 1975;

[5] Dubnyak S, Timchenko V. Ecological role of hydrodynamic processes in the Dnieper

Figure 16. Comparison between computed and measured velocity profiles in four cross sections.

The second category consists of errors related to the instrument, its volume resolution, the range of operation, and the sampling time. The ADCP device could measure instantaneous 3-D velocity vectors with 1% accuracy. The vertical resolution of the instrument was 0.05 m, which is less than the vertical mesh spacing (Δy) used in the numerical model, that is, 0.08 m. In other words, the instrument resolution error can be ignored.

The third category is related to the numerical methods (discretization and iteration errors), the boundary conditions, and the closure models. For a carefully modeled problem that has well-posed boundary conditions, these errors are relatively low in comparison with other errors.

The fourth category is how the model geometry was built. The modeled geometry was an approximation of the reservoir topography as it was based on measurements of discrete cross sections. The regions between the cross sections were interpolated and may not represent the right topography of the artificial lake. A rapid variation in the topography significantly affects the flow velocity distributions. The spacing used in the present study was selected with special attention to the section properties of the reservoir. However, they may not have captured important changes of the bed.

Based on the above discussion, a total error between computed and measured velocities of about 10% is a reasonable assumption. Proper agreement of theoretical and experimental results shows the correctness of the actions, developed in the frame of this work.
