Propuesta de investigación interna para determinar a competitividad de la

Shilton (2007) using a drogue tracking technique to determine flow fields in the ponds. The use of surface drogues for the measurement of water currents is not new, but they are more typically found in studies of larger water bodies with nearly uniform depth. Martin et al (1990) used drogues for their studies of advective transport in small aquaculture ponds; Shilton (2007) used the technique to study the speed and direction of the fluid movement in the model pond as many instruments were ruled out because of the very low velocities found in the ponds or the other instruments were expensive or not available for the project. The flow measurement software MatPIV, is similar but more flexible than drogue technique which can measure speed and direction of fluid movement in the diversity depth of model pond. MatPIV is a program written by Sveen (see Sveen and Cowen, 2004) and is based on 3 different sets of demo-images which are taken from the papers by Grue et al (1999) and Jensen et al (2001). It is one of at least three available, free toolboxes and is by far the largest presently available, both when functionality and number of users are considered.

Particle Image Velocimetry is a relatively old technique but it has only become a ‘digital’ tracking process within the last 15 years; it is an effective tool for the investigation of pond retention times and is considered to be a simple yet effective method of illustrating flow effects. Its use enables us to calculate the length of time for which water has been held in a pond. With this information gathered, one can start to gain an idea of the water quality in a pond and furthermore set about

making changes to the pond to achieve an optimum holding time. This review is intended to discuss the technical concepts on which PIV is based, the retention times for ponds and previous literature on and surrounding the subject such as:

a) Specifying the coordinate system b) Masking out regions of the flow c) Calculating velocities

d) Filtering the result e) Visualizing the results

Gurlek and Besir (2010) studied by means of PIV the flow structure around a rectangular body located close to a ground board in a free-surface water channel. The rectangular body was set with α= 0oand α= 10oyaw angles referenced to the flow direction and measurements were performed on the vertical and horizontal planes. The PIV technique provides instantaneous and time-averaged flow fields. For α = 0o, the results indicated that the flow structure in the wake region varied significantly with the elevation level from the ground surface. An asymmetric large circulating flow region was identified in the wake region for α = 10o. The instantaneous flow fields revealed the presence of small-scale-vortices in the main flow over the separation line. The vortices emerging from the leading edge of the model rotated in the flow direction, giving rise to entrainment between the incoming and wake flow regions.

In Rostami et al (2007), the study focussed on a comparison of both white light PIV measurements and empirical data and CFD simulation. The objective of the work was to assess the white light sheet PIV as a cost-effective and safe alternative for laser systems whilst keeping the accuracy limits required for

hydraulic model tests. The accuracy requirements for experimental work in hydrodynamics are usually less stringent than in aeronautical and mechanical engineering. Models in hydraulic engineering are larger, so that measurement volumes and light sheets can also be larger and wider. In addition, many hydraulic engineering laboratories consist of open spaces, so that the safety precautions required for laser work can be very difficult to implement. A white light (WL) source of PIV applications results in significantly easier experimental conditions as well as substantially reduced costs. It should be noted that the price of this system is very low when compared with using laser PIV model (almost 1:300). The development of a white light source for PIV applications means that experiments can be conducted with a standard PIV system in virtually any locations. The study shows that, based on WL PIV measurements, the mean velocity profile of each experiment had an excellent agreement with the empirical results. The comparison of WL PIV with CFD simulation velocities indicated that in a range of velocity between 0.095 to 0.194 m/s, the general error of the PIV measurement was an average of about 0.5 to 1.5%. This finding provides further evidence that WL PIV can be applied successfully in open channel flow analysis and open space experimental runs.

Hoyt and Sellin (2000) studied a comparison of PIV results with those obtained using a newly developed turbulent-flow tracer, for flow around a shallow- immersion cylinder and showed that the tracer and PIV displays give almost identical indications of the flow patterns. Since the tracer results are obtained on video, time-dependent streamline information becomes available, thus allowing detailed analysis of fluctuating flows.

Ismail and Ulrich, (2007) focussed on large scale PIV-measurement on the water surface for turbulent open-channel flows, in order to investigate the effects of processes in the water column on the dynamics of free surface flow. Three different sets of PIV measurements revealed a clear surface pattern of secondary currents of a second kind. The long-term temporal average of large stream-wise vortices in the water column results in relatively stable secondary currents of alternating sense of rotation scaling with water depth. Stable large stream-wise vortices always occur close to the sidewall and their successive superposition generates secondary currents in the long term. Vortex structures are detected from the instantaneous velocity map of water surface obtained by using a reference frame technique and from moving camera PIV measurements. Vortex visualization experiments show vertical motions with a vertical axis, mainly associated with up-welling regions of the secondary currents. The vortex size was found to be roughly equal to the water depth.