UNIVERSITI TENAGA NASIONALCIVIL ENGINEERING DEPARTMENTCOLLEGE OF ENGINEERING

CEWB 221HYDROLOGY AND HYDRAULICS ENIGINEERINGLAB REPORTEXPERIMENT NO 2:Mini Flow ChannelSection (no) :4

Group no. :1

Group members :ShafiqaSupinahBintiIjonartoni(CE093341)

ElliyaWafaBinti Abdul Hamid (CE093446)

Noor FahanaBintiBahruddin(CE093368)

Vivien Lai Mei Yen(CE093314)

Date of report submission :18/7/2014

Lecturer :Dr.Mohd Hafiz Bin Zawawi

TABLE OF CONTENTS:

ExperimentsContentsPage1Introduction2Objective3Apparatus4Procedure5Data sheet6Calculation8Discussion9Conclusion10Reference11Appendix

SummaryThe Mini Flow Channel is a simple experiment studying the phenomenon and pattern of the fluid flow over and around the submerged objects of different shape like triangular, cylindrical, aerofoil and rectangular shapes. This is achieved by using models such as small and large cylinders, narrow crested and broad crested weirs, crump weir and symmetrical and asymmetrical aerofoils. This experiment only takes into consideration 2 dimensional flow patterns.In brief, the model is fixed into the mini flow channel. Then, water is allowed to flow slowly into the channel. To avoid inconsistent flow of the water which will then result in unclear flow pattern, the flow rate of the water cannot be too fast. Next, the ink is injected into the channel, leading to ink flow in the water channel. Hence, the flow pattern over the model can now be visualized. The different flow patterns for objects of different shapes are sketched into the results slip and their stagnation points, areas of separation as well as the formation of eddies are also determined. The velocity of the flow in the channel can be adjusted by turning the valve situated below the Hydraulics Bench. The flow of the ink will exhibit different patterns according to the various velocities. For instance, turbulent flow (dye will flow in irregular path) will occur after flowing through the submerged objects when the velocity of flow is high. Different shapes of submerged objects used will result in different flow patterns. The location of the stagnation point is also different for different shapes of object.

IntroductionMini Flow Channel is an experiment used to introduce a simple demonstration of two dimension fluid flow of both over and around submerged objects of different shapes. Visualization the pattern of the flow is done by introducing ink for purpose of visual or photographic observations of flow along the bodies and placed any white paper behind the hydraulic bench. Besides, this may help for reveal the special features of flow such as stagnation points, separation and also formation of eddies. In this experiment, the study of influence of airfoil geometry on flow pattern is made by using 5 different wing shapes. The models of wing shapes are: Small cylinderNarrow and broad crested weirCrump weirAerofoilEach of the wing shapes will bring into different results of stagnation point, separation and type of eddy generation. Besides, the flow rate or discharge will also vital in affecting the results. This is meaning that even through in a same wing shape, it will cause different results when it is applied to a different flow rate.

Objective

To observe the flow phenomena and pattern around or over few models. To learn the stagnation points, area of separations and formation of eddies.TheoryThe study of flow around bodies of airfoil-like and other form is of great practical importance, since they are used not only as airplane wings, but form the basis of the design of blades for propellers, fans, pumps, steam, and water turbines. We shall limit our consideration to two dimensional flow patterns. The design of wing, propellers, turbines and blades is an important flow study on different body and shape. The maximum pressure intensity will develop in front of the object body where the stagnation point has a zero velocity. Thus, the thin boundary layer will establish at the stagnation point around the body. The end of the boundary layer will be the separation point where the flow starts turbulence.

For the turbulent flow, the eddy generation will usually occur after the area of separation for most of the cases. While, the turbulent flow passed through a sharp edge object might usually generate greater turbulent behind the object.Streamlines in flow are defined as lines at any instant, are tangent to the velocity vectors, there can be no flow across streamline at any point. Once streamline pattern is at hand, it is no longer necessary to include the individual velocity vector of fluid particles.The maximum pressure intensity is reached at the nose of the body, where the velocity is zero. This point is called a point of stagnation.

The separation of the flow from the surface of bodies is the direct consequence of the development of the boundary layer. In laboratory experiment this layer may be very thin and its presence cannot often be detected visually; the cylinder shown in Figure has diameter of 50 mm, and boundary layer, which starts to develop at the stagnation point in front of the cylinder, is still less 1 mm thick just ahead of the separation point.

It is possible to apply potential flow theory to the airfoil, leading the prediction of flow pattern of the kind illustrated in Figure. It is apparent that this flow pattern has peculiar features: there is a stagnation point on the upper surface of the airfoil just forward of trailing edge, and flow from the underside of the airfoil to the upper surface takes place around the trailing edge.

When the airfoil first begin to move (it makes no difference whether we consider the airfoil in motion, or the fluid motion), the flow pattern does in fact correspond to a potential flow. The establishment of the flow is accompanied by the development of boundary layers, and friction forces build up, the flow pattern changes. The result is that, at the trailing edge, two streams of fluid that are traveling at different velocities meet. The effect is to set up a lane of intense shearing a vortex sheet extended behind the airfoil. He shear forces set up n this plane act to equalize the velocities of two converging streams. This process takes place very rapidly, and is accompanied by the formation of a starting vortex resulting from the curling up of the vortex sheet. At a later stage the starting vortex is carried away downstream, leaving behind it the vortex sheet sketched in Figure.

The effect of the interaction between two streams is to accelerate the flow of the fluid in the upper layer and to reduce the velocity in the lower layer. In accordance to Bernoulli equation, the corresponding static pressure on the upper surface of the is diminished, and pressure on the lower surface is increased. At the same time the proportion of the fluid steam flowing above the airfoil increases, that flowing beneath decreases, and the position of the forward stagnation point is displaced downward.The lift Force F only develops when the flow pattern of Figure as been established, and is the consequence of the pressure difference between the upper and lower surfaces of the airfoil; this is a consequence of friction force.

Description of Experimental Apparatus

This experiment introduces a simple demonstration of two dimension fluid flow over and around submerged objects of different shapes. The visualization of low pattern is by introducing ink for visual or photographic observations of flow along the bodies, and reveal such special features of flow as stagnation points, separation and formation of eddies. In addition, the study of influence of air foil geometry on flow pattern is made possible by different wing shapes. Visualization the pattern of the flow is done by introducing ink for purpose of visual or photographic observations of flow along the bodies and placed any white paper behind the hydraulic bench.

HB 100 Hydraulics Benchis a basic unit which provides water supply and volumetric measurement services for use in conjunction with other accessories for specific experiments. The bench top is molded into an open channel and measuring tank with space for mounting accessories. The open channel discharges water into the measuring tank. This tank intern discharges water to main storage tank which can be drained by a bottom valve. Both bench top and storage tank are made of fiber glass. The measuring tank is stepped to enable accurate measurement of both high and low flow rates. Level indicators for water level in the open channel and measuring tank as well as Bulls eye level are provided to ensure correct position of the bench and accurate reading of the levels. Variable area flow meter to indicate instant flow rate is also available (optional).The equipment consists of mini flow channel, Hydraulics Bench, water and water ink. The mini flow channel consists of a transparent working section of large depth to width ratio having been varied by using of undershot and overshot gates at upstream and downstream ends, respectively. Water is fed to the streamlined channel entry from a stilling tank to reduce the turbulent intensity. Water discharging from the channel is collected in the volumetric tank of the Hydraulic Bench, and is returned to the stilling tank for recirculation. A dye injection system having 5 needles is located at the vertical inlet section of the channel allowing flow visualization in the conjunction with white background on the rear face of channel. The streamlines defining the direction of flow I the water are rendered visible by the injection of dye / ink at the upstream section of the channel.

Technical DataDye injection needles: 5Dye reservoir capacity: 0.5Width of channel: 15 mmLength of channel: 620mmDepth of channel: 180 mmPump: 0.5 HP centrifugal pump with flow rate at least 60 lt/min at 10 m headPower supply: 220 V, 1 Ph, 50 Hz.ModelsSmall cylinderNarrow crested and broad crested weirsCrump weirAero foil

Procedure1. The amount of ink dye was adjusted to be dropped to get a clear flow pattern.2. Try to have less body contact with the hydraulic bench to prevent vibration that might affect the smoothness of flow lines.3. Make sure the tap was closed. The nut was unscrewed which was situated at the center and slip in any of the four shapes object into the tank and slowly screwed it back.4. The knob was turned which stated below the hydraulic bench to get the flow that we desire. Turned more to obtain higher velocity.5. The flow patterns were observed and sketched it out.6. The tap was closed and waited for the tank to empty.7. The shaped of object was taken out and changed it with other shape.8. The steps 3 to 7 were repeated until all the different shapes are observed.Model for which it is necessary to study the flow pattern is in the channel at the determined angle of attack of put the water ink / dye in dye injection system on top of the tank reservoir. The flow of the dye and the height of the stream lines are adjusted to ensure full visibility. The flow velocity is determined by volumetric method. There is also a need to examine the position of undershot and overshot gates because they determine the level of fluid in the channel and the flow velocity. The best vertical (form observation five dyed jets must be seen simultaneously) position of 5 needles system been chosen, the features of flow pattern are analyzed. It is best to place the channel not on the Hydraulic Bench but on a separate table to eliminate vibration, hence streamlines formation. The channel discharge, however, should be still to the Hydraulics Bench.

ResultsSince there are no certain data or result for this experiment to be analysed or to be calculated, hence the pictures which show the different flow patterns will be analysed in this part of the report. For each picture showing a different flow pattern, there will be an explanation. However, the pictures or basically the flow patterns, limitations and the problems that are likely to disturb the flow pattern during performing the experiment will be explained again in the discussion part of this report. Point of stagnationPoint of separation

Figure 1: Flow Pattern around a crump weirmodel

Point of separationPoint of stagnation

Figure 2: Flow Pattern around an aerofoil modelPoint of separationPoint of stagnation

Figure 3: Flow Pattern around a small weir crested model

Point of separationPoint of stagnation

Figure 4: Flow Pattern around small cylinder modelPoint of separationPoint of stagnation

Figure 5: Flow Pattern around a broad crested weir model

DiscussionDue to blurry pictures, the results will not be as precise. This is also because of the dispensation of the dye were inconsistent. Hence, it has made it difficult to see the patterns properly and to take a proper picture. There was an error where the Hydraulics Bench was not in a level position as indicated by its bubble which was not in a centre position. This might have affected the flow of the water in the channel and the flow pattern of different shapes of the object.Furthermore, the error that was encountered is the inconsistency of water flow and that has affected the observations over the flow pattern of every different shapes of the object.ConclusionTo recapitulate each figures have different shape due to different shape of our flow pattern, the separation of the flow from the surface of bodies is the direct consequence of the development of boundary layer. Since the water is a transparent substance and it is difficult to see its flow pattern by the naked eyes, therefore some ink or dye is added in the water by special needles or dispenser in order to see and have a visualized picture and behaviour of the pattern of fluids flowing around or over a submerged object.

ReferencesHydrology and Hydraulics Engineering Laboratory Manual.