Experimental investigation of the Near Wake of a Trailer V. Barzanooni 1 2

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1 Experimental investigation of the Near Wake of a Trailer V. Barzanooni, A. Khoshnevis Mechanical Engineering Department Sabzevar Tarbiat Moallem Universit, I.R.IRAN Sabzevar-Tohid Cit Iran Mrvahid5@ahoo.com khoshnevis@sttu.ac.ir Abstract: In this paper we present results of an experimental program that aims at gaining a better understanding of the flow in the near wake of a trailer. We consider the effects of different velocit at the input on the trailer wake parameters. turbulence intensit and average velocit Charts is plotted for four different velocit. turbulence intensit and average velocit has been investigated B taking distance from the end of model. Analsis of the flow in the near wake of Trailer shows two maximum values for turbulent intensit because of the interaction between the shear laers of upper and lower surfaces of model and the wake region. Ke-Words: Experimental stud, Trailer, Hot-Wire, Near Wake, Wind-nnel, rbulence intencit, Shear laers Introduction Fluid flow measurement is so important phenomena in our industries. For measuring fluid flow, we can use some different methods, such as static pitot tube, hotwire anemometer, laser Doppler anemometer, ultrasonic anemometer and etc.each of them has their benefit, when the velocit variation are high and to measure the turbulence intensit of flow, the hot wire anemometer is velocit at high frequenc even over 3KH. So for turbulent flow and unstead flow measurement, hotwire has its own special abilities. Trailers are one of the more vehicle geometries in use toda et it has received ver littie attention in the car aerodnamics literature. The main goal of the present research is to gain a better understanding of trailer aerodnamics. The aerodnamics of road vehicles has frequentl been studied in simplified geometries to separate the effect of various components on aerodnamic drag and on near wake flow danamics. A review of earl work in this area can be found in Hucho[]. Particular relevant to the present work are the investigation b Balkanni and coworkers[,] on the effects of drag reducing devices on the near wake flow.recentl Leitz et al[3] have reported results of numerical simulation and experiments of the flow behind the tailgate of a pickup truck. Duell and George[5] report unstead flow effects in the near wake of a three-dimensional bluff bod with a blunt base similar to the one used b Balkani and co-workers.the differentiate between unstead effects in the separated shear laer at the edge of the bod and the closed recirculating flow region. In this paper we present results of an experimental program that aims at gaining a better understanding of the flow in the near wake of a trailer. We consider the effects of different velocit at the input on the trailer wake parameters. turbulence intensit and average velocit Charts is plotted for four different speed. turbulence intensit and average velocit has been investigated B taking distance from the end of model. Materials And Methods The experiments are done in the wind tunnel located at the department of design and manufacturing technolog, (Iranian research organization of science and technolog). this wind tunnel has settling chamber with series of mesh screen (mm ) and one hone comb with to make the airflow uniform. It is an open circuit low-speed wind tunnel made b Fara Sanjesh Saba Ltd, in Iran. and was used to simulate uniform air flow. The maximum speed of the tunnel is approximatel 3 m/s and the test section cross-section area is approximatel m and m length. the hotwire that we used in this stud is CTA tpe and manufactured b Fara Sanjesh Saba Ltd in Iran. Air passed through a contraction and a uniform flow passed through the test section with a free stream velocit of U. Data acquisition was done at different sections rear of model. rbulence intensit was. of the free stream velocit and the distribution of mean velocit was considered to uniform at the inlet of the test section(fig. ). ISSN: ISBN:

2 The x* stands for the stream wise dimensionless distance from the rear surface of the trailer model. Measurements were carried out b a constant temperature hot wire anemometer(cta) using a -D wire probe model from Fara Sanjesh Saba Co. the probe was maunted on a traversing mechanism that facilitated all three orthogonal movements. In order to move the probe in the test section, an open slot, with cm wide was made over the wind tunnel s topside. The probe positin in the streamwise and cross-stream direction was controllabele within. mm intervals b software. Before each test, the prob was calibrated for the range of.5- m sec with accordance to the conditions of the test room. Data analsis was made b special program called FlowWare. Ambient o temperature and pressure were ± c and 7 pa, respectivel. The signals from the hot wire anemometer were recorded with the digital data recorder at a sampling frequenc of 5 KHZ. The time-averaged velocit characteristics were obtained using about 5 samples. To test we used a model of two-dimensional and simplified bod trailer without details such as: mirrors, wheel and etc. The trailer model is shown schematicall in figure. as shown in figure, the length of the model is. m, and the height is.3m. the maximum cross section area is.m which gives a block age area ratio of 9% also shown in figure is the origin of the coordinate sstem used in this paper. The x-axis is in the flow direction. The -axis is in the vertical direction with its origin at the smmetr plane of the model. The scale of model is /75 and its height from ground is 5 mm. Air flow speed,5,, 5 m/s is tested. Fig.: schematic diagram of test section 3 Results And Discussion The flow characteristics are determined at streamwise(x) direction. u is streamwise velocit component that is non-dimensionalized using the free stream average velocit. The time-averaged velocities and the fiuctuating components of the velocit are processed using the related software. The free stream velocit is selected as m/s, 5m/s, m/s and 5m/s inorder to investigat velocit change effects on the wake characteristics. Figures to 7 show the profiles of time-averaged streamwise velocit, at different x* and different values of the free stream velocit. According to Fig., there is a velocit defect with increase free stream velocit, near the wake of Trailer. This defect is recovered at the first location(x*=.). Figure to 3 show the (turbulence intencit percent) for differend X/L ratio and different free stream velocit. It can be seen that the maximum values of turbulence intencit occur near the top edge of the model. This is due to the interaction between shear laers separated at the leading edge of the model and the wake formed behind the model. At first these maximum values increased and then are declined as the distance from the model increases. We see that the wake of trailer has an anisotropic nature. In additional, a high value of turbulence intensit can be as a result of vortex shedding. The values of wake turbulence intensit increase as the free stream velocit increases. But the maximum values of turbulence intencit at the far-awa from the model remains constant. Conclusion Near wake of a trailer has been studied experimentall at free stream velocities of,5, and 5m/s using Hot-wire anemometer. The distance from the model is varied so that the distance-tolength ratios (X/L) are.,.,,, and. Analsis of the flow in the near wake of Trailer shows that free stream velocit changes having an important effects on the wake velocit profiles except at the x*=.. there are two maximum values for turbulence intensit in the cases of x*=.,.. because of the interaction between the shear laers of upper and lower surfaces of model and the wake region.. ISSN: ISBN:

3 U=m/s U=5m/s U=m/s U=5m/s U=m/s U=5m/s U=m/s U=5m/s.... Fig.: profiles of time-averaged streamwise velocit component of the wake for x*=. Fig.5: profiles of time-averaged streamwise velocit component of the wake for x*=.. U=m/s U=5m/s U=m/s U=5m/s Fig.3: profiles of time-averaged streamwise velocit component of the wake for x*=. U=m/s U=5m/s U=m/s U=5m/s.. Fig.: profiles of time-averaged streamwise velocit component of the wake for x*=.. U=m/s U=5m/s U=m/s U=5m/s Fig.: profiles of time-averaged streamwise velocit component of the wake for x*=.. U=m/s U=5m/s U=m/s U=5m/s Fig.7: profiles of time-averaged streamwise velocit component of the wake for x*= ISSN: ISBN:

4 U=m/s U=5m/s U=m/s U=5m/s Y Fig.: profiles of turbulence intensit component of the wake for x*=. U=m/s U=5m /s U=m/s U=5m /s Y Fig.: profiles of turbulence intensit component of the wake for x*= U=m /s U=5m /s U=m /s U=5m /s Y Fig.9: profiles of turbulence intensit component of the wake for x*=. U=m /s U=5m /s U=m /s U=5m /s Y Fig.: profiles of turbulence intensit component of the wake for x*= U=m/s U=5m/s U=m/s U=5m/s Y Fig.: profiles of turbulence intensit component of the wake for x*= U=m/s U=5m /s U=m/s U=5m /s Y Fig.3: profiles of turbulence intensit component of the wake for x*= ISSN: ISBN:

5 5 List of smbols X: streamwise coordinate measured from the rear surface of the trailer. Y: vertical coordinate measured from the down surface of the trailer x*: streamwise dimensionless distance measured from the rear surface of the trailer H: height of the test section L : length of the trailer U: free stream velocit u: streamwise component of velocit : rbulence intencit percent References: [] Hucho, w.h., aerodnamics of road vehicles, SAE international, warrendale, pa, 99. [] Balkani, S.R., Bernal, L.P., Khalighi, B., and Sumantran, V.,"Dnamics of Manipulated Bluff Bod Wakes," AIAA paper -55,. [3] Khalighi, B. Zang, S., Koromilas, c., Balkani, S., Bernal, L.P., laccarino, G. and Moin, P., "Experimental and computational stud of unstead wake flow behind a bod with a drag reduction device,"saepaper --. [] Balkani, S., Bernal, L.P. AND KHALIGI, b.,"analsis of the near wake of bluff bodies in ground proximit," ASME paper [5] Duell, E.G. and George, A.R., "Experimental stud of a ground vehicle bod unstead near wake," SAE Paper 999. ISSN: ISBN: