Understanding Laminar and Turbulent Flow

Hello and Welcome This Blog from The Efficient Engineer is sponsored by Brilliant. One of the very first things you learn in fluid mechanics is the difference between laminar and turbulent flow. And for good reason.

What is turbulent flow?

these two flow regimes behave in very different ways and, as we’ll see in this blog, this has huge implications for fluid flow in the world around us Here we have an example of the laminar flow regime. It's characterized by smooth, even flow. The fluid is moving horizontally in layers, and there is a minimal amount of mixing between layers. As we increase the flow velocity we begin to see some bursts of random motion. This is the start of the transition between the laminar and turbulent regimes. If we continue increasing the velocity went up with the fully turbulent flow. Turbulent flow is characterized by chaotic movement and contains swirling regions called eddies. The chaotic motion and eddies result in significant mixing of the fluid. If we record the velocity at a single point in steady laminar flow, we'll get data that looks like this. There are no random velocity fluctuations, and so in general laminar flow is fairly easy to analyze. 

 Why is laminar and turbulent flow important?

For turbulent flow, we’ll get data that looks like this. This flow is much more complicated. We can think of the velocity as being made up of a time-averaged component, and a fluctuating component. The larger the fluctuating component, the more turbulent the flow. Because of its chaotic nature, the analysis of turbulent flow is very complex. Since the laminar and turbulent flow is so different and needs to be analyzed in different ways, we need to be able to predict which flow regime is likely to be produced by a particular set of flow condition We can do this using a parameter which was defined by Osborne Reynolds in 1883. Reynolds performed extensive testing to identify the parameters which affect the flow regime and came up with this non-dimensional parameter, which we call Reynolds number. It's used to predict if the flow will be laminar or turbulent. Rho is the fluid density, U is the velocity, L is a characteristic length dimension, and Mu is the fluid dynamic viscosity. The equation is sometimes written as a function of the kinematic viscosity instead, which is just the dynamic viscosity divided by the fluid density. The characteristic length L will depend on the type of flow we are analyzing. For flow past a cylinder, it will be the cylinder diameter.

At what Reynolds number is turbulent flow?

For flow past an airfoil, it will be the chord length. And for flow through a pipe, it will be the pipe diameter. Reynolds number is useful because it tells us the relative importance of the inertial forces and the viscous forces. Inertial forces are related to the momentum of the fluid, and so are essentially the forces that cause the fluid to move. Viscous forces are the frictional shear forces that develop between layers of the fluid due to its viscosity. If viscous forces dominate flow is more likely to be laminar because the frictional forces within the fluid will dampen out any initial turbulent disturbances and random motion. This is why the Reynolds number can be used to predict if the flow will be laminar or turbulent. If inertial forces dominate, flow is more likely to be turbulent. But if viscous forces dominate, it’s more likely to be laminar. And so smaller values of Reynolds number indicate that flow will be laminar. The Reynolds number at which the transition to the turbulent regime occurs will vary depending on the type of flow we are dealing with. These are the ranges usually quoted for flow through a pipe, for example. Under very controlled conditions in a lab, the onset of turbulence can be delayed until much larger Reynolds numbers. Most flows in the world around us are turbulent. The flow of smoke out of a chimney is usually turbulent. And so is the flow of air behind a car travelling at high speed. The flow of blood through vessels on the other hand is mostly laminar because the characteristic length and velocity are small. This is fortunate because if it were turbulent heart would have to work much harder to pump blood around the body. To understand why this is, let's look at how the flow regime affects flow through a circular pipe. The flow velocity right at the pipe wall is always zero. This is called the no-slip condition. For fully developed laminar flow, the velocity then increases to reach the maximum velocity at the center of the pipe. The velocity profile is parabolic. For turbulent flow, the profile is quite different. We still have the no-slip condition, but the average velocity profile is much flatter away from the wall.

Why is turbulent blood flow bad?

This is because turbulence introduces a lot of mixing between the different layers of flow, and this momentum transfer tends to homogenize the flow velocity across the pipe diameter. Note that I have shown the time-averaged velocity here. The instantaneous velocity profile will look something like this. In pipe flow, one thing we are particularly interested in is pressure drop. Across any length of pipe, there will be a drop in pressure due to the frictional shear forces acting within the fluid. The pressure drop in turbulent flow is much larger than in laminar flow, which explains why the heart would have to work harder if blood flow was mostly turbulent! We can calculate Delta-P along the pipe using the Darcy-Weisbach equation. It depends on the average flow velocity, the fluid density, and a friction factor f. For laminar flow, the friction factor can be calculated easily. It is just a function of the Reynolds number. If we combine these two equations we can see that the pressure drop is proportional to the flow velocity. But for turbulent flow calculating f is more complicated. It is defined by the Colebrook equation.

What is laminar flow used for?

appears on both sides of the equation, so it needs to be solved iteratively. Unlike laminar flow, for which the pressure drop is proportional to the flow velocity, it turns out that for turbulent flow it is proportional to the flow velocity squared. And it also depends on the roughness of the pipe surface. Epsilon is the height of the pipe surface roughness, and the term Epsilon/D is called the relative roughness. Surface roughness is important for turbulent flow because it introduces disturbances into the flow, which can be amplified and result in additional turbulence. For laminar flow, it doesn't have a significant effect because these disturbances are dampened out more easily by the viscous forces. Since the Colebrook equation is so difficult to use, engineers usually use its graphical representation, the Moody diagram, to lookup friction factors for different flow conditions. Where flow is laminar the friction factories only a function of Reynolds number, so we get a straight line on the Moody diagram. For turbulent flow, you select the curve corresponding to the relative roughness of your pipe, and you can look up the friction factor for the Reynolds number of interest. So we know that if the Reynolds number is large, inertial forces dominate, and the flow is turbulent. 

But even for turbulent flow viscous forces can be significant in the boundary layers that develop at solid walls. Because of the no-slip condition, shear stresses are large close to a wall. This means that in a turbulent boundary layer there remains a very thin area close to the wall where viscous forces dominate and flow is essentially laminar. We call this the laminar, or viscous, sublayer. Its thickness decreases as the Reynolds number increases. Above the laminar sublayer, there is the buffer layer, where both viscous and turbulent effects are significant. And above the buffer layer, turbulent effects are dominant. If the roughness of a surface is contained entirely within the thickness of the laminar sublayer, the surface is said to be hydraulically smooth, because the roughness has no effect on the turbulent flow above the sublayer. This is important in pipe flow because, as can be seen from the Moody diagram, flow in a smooth pipe has a lower friction factor and smaller pressure drop than flow in the rough pipe.

Understanding Approach of an AStabilizedircraft!

Hello and Welcome what is meant by the Stabilized approach of an aircraft before we look at what is meant by a stabilized approach let's look and why an established approach is required for the advantages of waste plastic Road if the approval is developed it in a safe landing on aircraft which is landing at the correct speed and attitude text approach the completion of the landing rule within the available Run will and all the available and in the stands with the established approach by the can avoid a loss of control of the aircraft during approach which is more critical if there is any Terrain surrounding the Runway and finally a smooth flat maneuver can be initiated by the Pilot approach is stabilized.

what is meant by a stabilized approach?

during different ways which come just before the flood and the landing room if the Agra satisfies a set of conditions that your project is called as a specialized approach a few of these conditions are approved speed heat of the 10th landing configuration and aircraft attitude and engine trusting let's look at this condition in more detail

the approach speed during the approach face the aircraft must be of you not faster than desired touch on speed depending on the aircraft manufacturer of this may be defined as we approach or f speed will be at least 1.3 times more than the stall speed of the aircraft for a given landing configuration the rate of different this is regarding the approach angle and the rate at which the aircraft is descending usually the approach angle would be three degrees and the rate of this and would be between 600 to 700 feet per minute the maximum rate of the send for established approach will never exceed 1054 minut in all cases landing configuration the act should be fully configured for landing which is with respect to the flaps and the landing gear in normal flying conditions for a stabilized approach the flaps to be extended family and the landing gear should also be extended it should also be ensured that they are not in their respective positions the aircraft attitude the egg craft must be stable on all the three Axes and only minor corrections may be allowed if required due to external factors during the approach base the potential energy of a graph get converted into kinetic energy so proper Energy Management is essential for the smooth and safe landing the eggrat attitude plays a major role in the total energy management for Ireland is used for your product should have captured and aligned with the localizer and glideslope signal of the Runway in which the aircraft has to land the wireless assist the aircraft in being supplied on the final Descent path

aircraft is descending the engine can be reduced but the engine should be stable and it was provided by the engine will be a little above I will be idle Indian forced applies to produce these conditions should be satisfied depending on whether the aircraft is grown under instrument conditions IMC or visual met conditions VMC there is an altitude limitation by which the aircraft should be stabilized and I am see the aircraft should be stabilized by thousand feet and under VMC the aircraft should be supplied by 500 feet IMC and VMC are defined based on visibility distance from my cloud and ceiling During these conditions are not satisfied it is always best to perform a go around and make a new attempt for landing aircraft they may be many reasons why the approach becomes hand on supplied approach let's take a look at a few of the reasons some of the reasons for an unfertilized approach for visibility adverse weather conditions through fatigue failure of my receiver on both the aircraft any ATC restrictions tureen t enough to go near the airport

WHY do pilots say HEAVY? Wake Turbulence

Hello, and welcome Now I'm pretty sure many of you have seen airplanes approaching airports all lined up like pearls on a necklace Coming in one by one. Now, they seem to be all flying at a safe distance from each other as this is the work of the approach controller. Now he makes sure that the airplanes have enough separation from each other by vectoring them with given headings and controlling their speed onto the instrument landing system. Now the planes land as such that they have enough time to vacate the runway at the suitable taxiway before the next plane comes to land.  an Airbus A320 is just landing and you can already spot the next airplane, a Boeing 777, right behind it.

But the reason for this separation is not just the time to vacate the runway, actually, the primary reason is wake turbulence avoidance. So what is wake turbulence? Now, wake turbulence or wing vortex occurs when the wing is generating lift. Now, if air below the wing is drawn around the wingtip into the region above the wing by the lower pressure on the upper side of the wing Causing a vortex to trail from each wingtip. Now the strength of the wingtip vortex is determined primarily by the weight of the airspeed and the angle of attack of the aircraft. Now the higher the angle of attack and the heavier the plane, the stronger the wake turbulence becomes. turbulence but keep in mind this is only an ultralight airplane with a maximum weight of roughly 450 kilos, but it's impressive how quickly the wakes appear. So imagine the wake turbulence a Boeing 747 generates with a maximum landing weight of 302 tonnes and wake turbulence is a serious threat for the preceding plane.

Nasty downdrafts and sudden excessive roll rates get the plane in an upset state you do not want to experience on short final as a pilot or as a passenger. Numerous testing has shown that wingtip vortices have an estimated sink rate of 400 feet per minute and come to rest at 800 feet below the airplane's flight path where it is considered safe to fly across the dissipating wake. So let's determine the minimum separation needed between two Airbus A320's now we are definitely going to need two minutes and that is the time it takes to wake to descend 800 feet and Two minutes at an average approach speed of 130 knots results in 4.3 nautical miles minimum separation distance now at 64.5 times maximum landing weight the A320 is not the heaviest aircraft out there. So the ICAO came up with the wake turbulence Weight categories now write this down because these numbers will be in your HPL exam. Category L is for lightweight - So any plane up to 7 tons or less. category M for the medium is for 7 tonnes up to a hundred and thirty-six tons and Anything heavier than that is categorized as heavy, but as usual, there is an exception So listen to the ATC call of my dear friend Paulo Alexander Bukarest control, very good morning Qatar 13VP "SUPER" at level 390 As he flies the Airbus A380 ICAO had to introduce a new category for aircraft with a take of weight up to 560 tonnes named Super, so as mentioned a minute ago the heavier the plane the larger and more intense the wakes are the more separation is needed between the planes.

now British Airways 777 has just landed categorized as heavily followed by a medium category Airbus A320 now you can see there's a significantly larger gap between both airplanes and as ICAO regulates if a medium follows a heavy aircraft Their minimum separation has to be 5 nautical miles now This can go up to 8 nautical miles for instances a light aircraft like a Cessna Caravan follows an Airbus A380. But if a heavy aircraft follows a lighter aircraft they aren't affected as much by the wake due to the Actual heavier weight and are safe at a distance of 4 nautical miles. But it's not just the ATC controller's responsibility to vector you accordingly you as a pilot have to keep the necessary distance in order to not get into the wake turbulence of the preceding aircraft. But how do you know as the pilot? What type of plane is ahead of you? And this brings us to the main question of the video. That's the reason why pilots flying airplanes categorized as heavy creating the more severe turbulence mentioned their category at the end of their call sign So as a pilot, you should pay close attention to who you following Especially when intercepting the ILS at a lower altitude than your preceding airplane and wakes aren't just a threat during landing; a similar procedure applies during takeoff now very often you can see a heavy Airbus A330 departing and then a smaller Boeing 737 or Airbus A320 waiting on the runway for their takeoff clearance and the waiting period is a safety measure to let the wake turbulence dissipate before the lighter aircraft commences takeoff. Now you say that's not true I've seen turboprops rolling down a runway right after a heavy has taken off. Yes, that's true this can happen but there's something very important to keep in mind Wake turbulence as mentioned before are first Generated when the plane rotates meaning creating lifts over the wing so if the turboprop pilot closely monitored the lift-off point of the preceding plane and Knows his takeoff roll will be shorter He can immediately commence takeoff as he will fly over the flight path and wakes of the preceding plane also During cruise flying through the contrail of an aircraft can get very turbulent So avoid flying through those especially with passengers in point Now these strong rotors upon landing are no joke They are so powerful that houses close to airports have to have special roof tiles as in the past They have caused many damages Especially if you're in flight school and feel the need to fly to a big international Airport for a low approach with your little Cessna and besides the tower control that will warn you about the wakes.

Keep a safe distance Because getting flipped over by awake isn't cool at all. And if it doesn't feel safe you can always Go around also be aware of hovering helicopters in the vicinity of the runway There wakes can be as powerful as a medium categorized aircraft. And by the way, speaking of flight school Have we ever thought why a glider plane always flies a little higher than its preceding tow plane Think about it and as always Concord had her own rules although Concorde fell into the category of a medium-weight Aircraft due to her excessive angle of attack upon landing Her delta-wing created wake turbulence as strong and as dangerous as the ones of jumbo and therefore the pilots had to say speed bird Concorde too heavy! God, I miss this plane That's it for today Thank you very much 

What Is Meant By Contrails? The Reason For Contrails ? What Are The Major Sources of Contrails ? That Formed At The Engine Inlet?

Hello and welcome we will be looking at what is meant by contrails  the reason for contrails and what are the major sources that formed at the engine inletLet's see what is meant by contrails Short for condensation trails or vapour trails  that can be seen downstream of a jet engine exhaust contrails are something that occurs naturally and depending on the atmospheric conditions it may form in an aircraft is flying at a very high altitude at a lower altitude as well but they can be some smoke trails that can be man-made 

Usually, the aerobatic aircraft that a flying liver smoke trail behind them this trail is man-made and does not depend on the atmospheric conditions the smoke is created by spring degradable paraffin-based oil at the engine exhaust because of the high exhaust gas temperature the oil will immediately vaporize living a smoke trail behind the aircraft another method is to use a separate motor generator that will create the smoke train to the different nozzle at the trailing edge of the aircraft the oil that is used should be non-toxic and should not cause damage to the aircraft or effective Pilots of the audience the smoke that is created also gives a visual idea to the pilots about other aircraft rectory and can assist the making corrections as required

Now let's look at the reasons for contrails  formation

as be so earlier the contrails forms naturally behind an aircraft one of the reasons for contrails   formation is because of the mixing of hot humid air from the engine with exhaust outside air which has low vapor pressure and low temperature The hot humid air immediately condensers because of the outside and conditions and freezes immediately causing a white trail behind the aircraft the size thickness and duration of the country depends on the aircraft altitude the temperature and humidity of the atmosphere these contains  are usually seen on aircraft flying at very high altitude

Some contrails  may be seen on aircraft flying at lower altitudes these contrails  are mostly formed at the training age of the flaps of the wingtips  and not necessarily at the engine exhaust and the trailing edge of the flaps and the wingtips what is this are created behind the aircraft these vortices cause A reduction in pressure and temperature which can cause the water in the air to contents resulting in visible contrails these contrails  also depend on the humidity of air but will usually occur at lower altitudes when the aircraft is flying at slow speeds

Now let's see what is meant by chemtrails

according to some people are chemtrails chemical smoke trails  which are spread by an  aircraft in flight over certain places toxic Chemicals were loaded on aircraft based on inputs from certain people there is no evidence which supports this and a more specific system is installed on the aircraft for spraying Chemicals except for a few aircraft used for crop cultivation so we can conclude that chemtrails do not exist

Now we will look at what are the smoke trails

which are created at the engine inlet these trails are called an inlet. vortex and occur when the aircraft is on the ground and stationary or moving at slow speeds and the engine is creating high thrust this vortex extends from the ground and enter the engine through the engine  diffuses action the vortex that is formed with contents the air creating a visible vortex trail at the inlet as shown here so this would this is also depending on the humidity of the outside air but this vortex trail may affect engine operation with other countries do not affect the engine of the aircraft