Human beings differ according to their passion, desire, and aim therefore the tools that we have used for centuries diverge as to satisfy our demands. This divergence can be seen in every field of daily life. Some of those tools are ushering by trends that I guess you have had lots of them so far. The trend is an illicit drug and we are behind the bar to reach at least a piece of them with our average budgets. Some call it economic harassment. Anyway, having a thorough interest on cars since my infancy, I, though, can say that that bulky plastic and metal tools are one of my illicit drugs, especially coupe and convertible ones. Fluids dynamics is my dearly curiosity that develops my interest making me a meddlesome engineer. Throughout this article, I’m going to investigate the aerodynamics of a convertible can and compare it to the coupe one. Despite the fact that convertibles are summer stuff, a guest from Germany (see figure 1) has broken all my bounds that the driver was trying to go on and on amid the snowy winter conditions. It is bizarre that, of course, windows were fully closed due to winter. It would have been a great bliss that air conditioner was on at 27 degree Celsius. Figure 1 The first question that come to my mind was the velocity at which windshield may negate the effect of snow. What would the conditions both driver and passengers encounter? “The Slow Mo Guys”, a YouTube channel, has examined the effect of rain experimentally. In the video below, they use a convertible BMW 2 series: I cannot interpret anything from the video above since they didn't give any result or comparison among their experimental campaign. Despite, it is funny to observe the physical incident with a slow motion camera where it is hard to find a convenient one for an enthusiast. Another experimental examination regarding convertible car aerodynamics belongs to GraysGrage. I recommend you to follow the channel that Gray shares excellent videos regarding ground vehicles and aerodynamics. He has been carrying out wind tunnel tests as to determine aerodynamics of cars and try to testify effect of several kinds of stuff on aerodynamics such as spoilers at bonnet, roof, and rear. Graysgarage compares convertibles and auxiliary structures such as wind deflector regarding location and size. You may have seen a wind deflector as in the picture below if you encounter someone who has a convertible and tries to get rid of back-flow (?). Figure 2: The wind deflector which is located over back seats It is time to have a deep dive into theory. Technically speaking, the separation throughout the boundary layer results in chaotic flow which is defined as Turbulence, the flow condition hardly ever foreseen. For convertible cars, airflow after windshield cannot stand any surfaces to keep on movement through trailing edge without flow in the reverse direction. The back-flow, flow in the reverse direction, is occurred some distance later windshield and directly influences both passenger and driver, although headrests are available. Hence, the application of a wind deflector provides pleasure driving which reduces consequences of aerodynamics instabilities. Moreover, the difference between the aerodynamics of cars either with wind deflectors or not can be seen in figure 3 as follows: Figure 3: Experimental examination of wind deflector The shape of cars is an exploratory issue that is indeed associated with fuel consumption, acoustic, and stability. The drag coefficient is one of the main factors which defines the degree of frictional force as to specify relation between flow and solid structure. According to Wolf-Heinrich Hucho (2013), the drag coefficient through optimal body to road vehicle can be seen as in graph as below (figure 4). The difference between saloon-, coupe-, and convertible-type cars is also specified as below (figure 5):
Aside from literature, most of them based on studies of enthusiastic, I have conducted some CFD studies to examine difference between coupe and convertible. Besides, I have also carried out studies to further investigate a presence of rear spoiler. For this purpose, I have gotten 2D model of BMW 4 series and generated 4 models with and without rear spoiler. Figure 6: BMW 4 series with rear spoiler and BMW 4 series convertible both open and close The parameters and definitions on numerical study can be concluded as follows:
Models:
As expected, the minimum turbulent kinetic energy among model belongs to model 1 which has rear spoiler. The foil of the spoiler is NACA airfoil 0012 which is selected arbitrary. Figure 7: CFD comparison Results: According to CFD results which can be seen as in Figure 7 and video below, a huge ascent in the turbulent kinetic energy is generated at car with open-roof. Both of open- and close-roof cases, application of spoiler reduces the magnitude of the turbulent kinetic energy. It is obvious that the passenger at the back seats would be effected by turbulence at the velocity of 80 km/h which also causes a poor aerodynamics that results in increasing of fuel consumption and noise. Therefore, application of wind deflector would really reduce the effect of turbulence. Yet rear spoiler has a positive effect to negate the presence of turbulence, it is insufficient to prevent boundary layer separation. Thus, it would have been an affirmative solution to using a rectangular plate over the upper-side of windshield (see the bonus below for details). Here is detailed video with velocity contours: Bonus: Have a further idea, please comment below!
© 2016 -2017 Sersol. All rights reserved except where noted.
0 Comments
Tough viscosity is driven under the factors such as temperature, molecular structure, shear rate, ambient conditions, and even flow conditions, it isn’t, partially, related to weight. The existence of matter consists on molecular structure which has a specific weight and also bond to create bulky structure. To examine detailed description on viscosity, you had better to check my previous article on it: Viscosity Amount of matter has no any effect of viscosity that the viscosity of a cup of water and a ton of water is same. Besides, I also wonder about comparison among substances in which the viscosity and density change in accordance with matter. Here is a compatible graph that compare several substance (I got the values from engineering tool box): Here is a video that compare biodiesel, glycerin, and vegetable oil: The viscosity only needed to weight for the purpose of existence, not much. Whole description is convenient for Newtonian fluids.
Multiphase examination of ascending of hydrogen bubble in the water during the electrolysis where hydrogen is the product of the chemical incident. The bubbling process has been generated by UDF in which chemical process partially simulated. The study is relatively related to bubble growth, accumulation, and detachment. Tool: Ansys 16.2 Fluent Numerical Model: Eulerian - Multiphase flow approach / Sharp General: Transient, 2D, and Gravity. One of the important reasons of fluid movement is pressure difference. Bulky fluid tends to flow high pressure side to low pressure-side. It is a bliss that physics have awkward methods. The Marangoni Effect, one of them, is a special case that explain interaction between fluids and surface tension. Before explanation regarding Marangoni effect, it had better to get a semi-touch with surface tension which is the interaction through boundary between liquid and air. It provides the least surface to liquid through boundary due to inter-molecular forces. "At liquid-air interfaces, surface tension results from the greater attraction of liquid molecules to each other (due to cohesion) than to the molecules in the air (due to adhesion). The net effect is an inward force at its surface that causes the liquid to behave as if its surface were covered with a stretched elastic membrane. Thus, the surface becomes under tension from the imbalanced forces, which is probably where the term "surface tension" came from. Because of the relatively high attraction of water molecules for each other through a web of hydrogen bonds, water has a higher surface tension (0.072 N/m at 20 °C) compared to that of most other liquids. " For instance, the surface tension of soap is lower than water. Therefore, while an amount of soap droplet is poured into the water, molecules of water are triggered to flow ahead liquid soap due to difference of surface tension. I have conducted an indoor experiment which is easy to carry out, as below: Physics is an illicit drugs that make people meddlesome. Have much fun. Whereabouts does absolute zero come from ? Yet it seems virtually has a deep science, if you familiar with thermodynamics, it is easy to explain the phenomenon. Where are the proponents of the Carnot Cycle ? Quasi-technically speaking; Here we go. It is the convenient explanation that the Carnot cycle is the base for absolute zero. We all seem to agree within this physical phenomenon. What about others ? How would have you explained the absolute zero someone who has a background out of science ? Follow me. Here is the a convenient explanation of "absolute zero" in a relative technical perspective. Were you to being experienced with thermodynamics, It would be easier to understand phenomenon. Moreover, we could interpret absolute zero as to constitute a connotation. It sometimes seems elusive to generate a rapprochement to physical phenomena. I prefer "Loudspeaker" to describe absolute zero. Although there is a lowest value for temperature which is specified 0 degree Kelvin, there isn't any specific value for the highest yet. While temperature of bulk goes down to 0 degree Kelvin, efficiency of Carnot machine goes up to 1 that is the highest value for efficiency (Efficiency of system varies between 0 to 1 regarding to temperature). Anyway, now forget about it and turn back to loudspeaker. You are a teenager and probably obsessive on rock music. Have you ever wondered to playing guitar ? It is such an idea needs curiosity, passion and ear. Do you aware of huge amplifiers that rock bands use in their concert ? These amplifiers consume relatively huge amount of energy to release voice. If you turn off volume or try to keep it through a lower level, amount of consumed energy decreases. You can't go further that there is a lowest value for volume level is 0. No energy is consumed to generate voice that zero is same for each us to specifying silence. What about the highest level ? Yet I haven't a precise information, 194 dB is assumed as the maximum value at 1 ATM in accordance with literature. Therefore, maximum level could be changed regarding to power of amplifier and ambient conditions. Having further question, do not hesitate to contact !
We all know that temperature change is the main effect on viscosity since it is easy to observe results of changing of viscosity regarding to temperature change. Imagine it is a happy weekend day breakfast and you are one of them who keep cream chocolate out of fridge, yes Nutella (Some of keep it in the fridge). Having forgotten Nutella in the fridge the day before, the resistance of chocolate against flow would increases and you should have to wait until it gets warm. Surveillance is great! Temperature is one of main actors as to change viscosity. What about the others ? How do viscosity occurs? Every now and then, you would consider the other parameters if you have not a exact knowledge about them. We ought to examine the factors whereas viscosity changes regarding to changes these ones. Apart from temperature, some of properties are partially effective on viscosity. These are Molecular Structure, Shear Rate, Ambient Conditions and Flow Conditions. Also, those factors could effect each other as to cause various physical phenomenon. Molecular structure: Assume that molecular bonds of ingredients in honey structure probably might be higher than the ones. The tighter the molecules are linked, the more the substance will resist deformation. Shear rate: Newtonian liquids are independent of the external force. The vital question is whether a change of shear rate does or does not change a fluid's viscosity. This question draws the line between Newtonian and non-Newtonian fluids. If a fluid's internal flow resistance is independent of the external force – i.e. the shear rate - acting upon the fluid, it is ideally viscous. Such fluids are named Newtonian liquids after Sir Isaac Newton, who discovered the mathematical relation between viscosity and the external force acting upon a fluid. For non-Newtonian Liquids, If a substance is not ideally viscous, its viscosity changes with the shear rate. Their viscosity decreases when the shear rate increases. For other substances the viscosity increases with increasing shear rate (i.e. yogurt, body gel, starch) The ambient conditions: Apart from temperature, the pressure could be effective on viscosity within particular conditions. In most cases, a fluid's viscosity increases with increasing pressure. Compared to the temperature influence, liquids are influenced very little by the applied pressure. The reason is that liquids (other than gases) are almost non-compressible at low or medium pressures. For most liquids, a considerable change in pressure from 0.1 to 30 MPa causes about the same change in viscosity as a temperature change of about 1 K (1°C). Consequently, the molecules can move less freely and the internal friction forces increase. The result is an increased flow resistance that might be ignored. The Flow Behavior of Water under Pressure: The anomaly that water has its maximum density at +4°C is widely known. Such an anomaly can also be observed for the flow behavior of water under pressure. For temperatures >+32°C, water behaves like other liquids. Its viscosity increases with increasing pressure. Below +32°C and under pressures of up to 20 MPa, the water's viscosity decreases with increase. Flow Conditions: For testing a fluid's viscosity, defined flow conditions are essential. The fluid has to develop laminar flow. With laminar flow, the substance moves in imaginary thin layers in which molecules do not change from one layer to another. The flow has an orderly structure. In turbulent flow, on the other hand, no recognizable structure or layers can be observed. Molecules move freely. The fluid forms vortices. If testing a fluid under turbulent flow conditions, the results will give a falsely higher viscosity. (The turbulent movement of the molecules will be misinterpreted - so to speak - as higher flow resistance by a measuring instrument). Here is a short video related to viscosity and how to measure it. Enjoy your watch: An examination of Karman Vortex phenomenon has been carried out, previously -> Click The Karman Vortex Street is one of particular specifications of fluid physics at which can be investigated numerically. There are lots of experimental and numerical studies that have been carried out since it had been discovered. In this topic, I wanted to share numerical simulation results which I have carried out in accordance with experimental study of Sanjay Kumar and George Laughlin from Department of Engineering, The University of Texas at Brownsville. The researchers carried out this experimental work due to receipt effect of spinning object on Karman Vortex Street. Besides, they also detected the structure of Karman Vortex during stationary condition of circular object. The experiment had been realized with the values specified as below: Diameter of circular object: 6.35 mm Reynolds Number: 168 Working fluid: Water Three specification mentioned as above are enough to generate a numerical solution related to Karman Vortex Street. I have generated a numerical model within Ansys 16.2 commercial software (SpaceClaim, Meshing, Fluent). Consequently, a comparison between numerical and experimental result has been visualized. The photograph as below is captured by Sanjay Kumar and George Laughlin during stationary condition experiments: Verification and validation are the most important specification of a numerical study. Weather or not, a numerical study has to be examined with these two phenomena. On the contrary, simulation results might only available for a painting exhibition. What are the verification and validation ? Anyway. Results and comparisons of specified studies has been visualized as below: The pattern after circular object is mostly similar with experiments. Some of parameters could be adjusted to reduce error rate and ambiguity.
To sum up, CFD model that is generated myself is applicable (validation) in accordance with this case. Thus, it probably works in which other model through different scales.
We all has been carrying out experimental studies since birth as to understanding physical phenomena. Remember your tremendous examinations with water, sand, earth, etc. What happened during your infancy ? At first, you probably could detect something quite different around you which triggered your curiosity. Thus, observation process had been started at which you would want to define physical phenomena. Were to observed only, you would be specified as a quite observer like peer. On the contrary, some of us had conducted experimental studies as to examined several specifications that are partially effective on the physical phenomena (These children were called as hyperactive or even something else). I was one of them had lots of injures through different areas of my body. One of my obsession was related to crash simulation. I had various mini plastic toy cars and was carrying out several experiments with them (crash, burn, race, swim, etc.).
Humankind needs experiments to getting a deep dive regarding world. We have observed, have carried out experimental studies and have generated analytic & numerical model to specify problems and we will be. Recently I have discovered a Youtube channel includes various spectacular experimental fluid mechanic videos. Even if some of them seem like a horror film, all these studies are marvelous. I suppose that you would much enjoy with these videos. Here is 35 videos in this channel that are between 4 mins and 10 mins. There is something wisdom. All best. An airplane that the most fastest way to travel among distances. In accordance with statistic, the most reliable vehicle related to public transportation is airplane. Although, we have been encountering several crashes that probably result in carnage as to a death tool in recent years. What about the Malaysian Airplane which have been searching for 3 years ? Therefore, some entrepreneurs are in their way as to create novel, applicable and also cheap designs. According to statistic, the possibility to being killed in an airplane is 1 in 29.4 million. Even if you may encounter with a death crash, the probability to being rescued is around 24 % which is higher than my foreseen, frankly speaking. Have you ever wondered which action of airplane is most dangerous ? Let's grabbing statistic: 16% of total crashes are associated with "cruise". Distribution of percents are in balance which clarify danger comes through in every way. "Detachable aircraft cabin" is virtually a novel design but would it be a solution ? What will captain do if the trouble starts during takeoff ? Will captain drop the cabin above to structure as to apartment, residence or workplace ? "Tatarenko Vladimir Nikolaevich" has 2 patent applications so as to detachable aircraft cabin design. Let's have a look: Is it safe ? I'm not sure yet. What if someone was carrying out a simulation regarding to detachable cabin. "A youtuber" has done it. Even so, It might not an exact simulation as to scientific laws but would be an reasonable sight to discover. This is: If you have a further explanation, comment below ! Thanks. Controlling process needs a board in which ingredients are located to sustain communication between device and controller. Design of electronics circuits on the board is an important case. CPU, capacitor and the others, of course, get active with electricity. Location of these ingredients on card are determined based on board area and interaction. While specifying locations of ingredients considering criteria, thermal equilibrium, generally, isn't being considered as a problem that is actually a big problem. There is no censure for anyone who comes from one of electronics departments unless designer familiar with thermal system.
There are various commercial CFD software at which electronics cooling studies might be carried out. Even, Ansys has a particular software regarding to electronics cooling is called as Icepack. If there is no facility to using Icepak, you have to design your own case with others. What are the criteria at which we have to be careful ?
What else ? I advice you to examine project of Simscale that gives you a compatible sight: Click: Simulation Experts Save Electronics from Thermal Damage Click: A project of simscale Also click: MODELING OF NATURAL CONVECTION IN ELECTRONIC ENCLOSURES |
Categories
All
|