Low-speed Circulating Wind Tunnels Essay

In this experiment, the velocity profile for a flat plate at zero pressure gradient of a boundary layer at two different stream wise points were acquired. The investigation was also based on and how changes in Reynolds number affect the velocity distribution within boundary layers. Parameters such as the Momentum Thickness, Displacement Thickness, Shape Factor, shear stress and coefficient of friction was also calculated to gain a better understand of boundary layers. The experimental values calculated were compared to the theoretical Blasius for laminar flow and Power Law Solutions for turbulent flow to see how they varied. It was found out the higher the Reynolds number the greater the boundary layer thickness. As the

A Betz manometer is used to measure the tunnel pressure, which is given in mm0, which can then be used to calculate the wind tunnel speed. This pressure was given as 20.25 mm0. The barometric pressure was recorded to be 761.5 mmHg, which will be converted into Pascals. The ambient air temperature was taken to be 23.5

Additionally, lower-mantle plume conduits rooted in wide patches of strongly negative velocity reduction were found in Hawaii, Iceland and Samoa (p. 96). Figure four of Frenchs’ research revealed that eleven major hotspots possessed plumes with notably similar characteristics. Visual inspection of these similar plume conduits indicate that they may derive from very broad, lower-mantle domes (p. 97). Nonetheless, French notes that there are corresponding plumes that are below the detection ability of current imaging technology, making it difficult to make any concrete assumptions (p. 97).

The inspiration of using riblets for drag reduction came from the study of sharks. Upon calculation of the Reynolds number of a shark based on its body length, it is found to be very high, of the order 106–107.3 In spite of this fact, sharks are extremely fast swimmers, which is disproportionate to the maximum speed they can achieve based on their body mass and area. On further investigation of the reason behind this anomaly, it was found that shark skin has certain microstructures that reduce drag. Though shark skin appears to be extremely smooth, it has minute grooves or microstructures on the surface. They have tiny scales that are about 0.2–0.5 mm, with ridges that are aligned in a “streamwise direction”.3 Each scale has about 3–7 ridges. Laboratory tests reveal that because of these scales that extend into the turbulent boundary layer, about 7% reduction in drag is achieved.3

The first part of this experiment involved testing three wing designs in a wind tunnel. First, the wind tunnel was turned on with nothing inside and the flow velocity was recorded. Then, the first airfoil, a pre-built standard NACA 0024, was tested. It was put in the wind tunnel in the 0° slot on the Kelvin Lift & Drag Balance arm and locked in place. The balance was then calibrated so that the LIFT value read zero, and the wind tunnel was turned on to its high setting. Once the wind tunnel reached its maximum speed of approximately 6 m/s, the value for LIFT was recorded and the wind tunnel was turned off. These steps were then repeated but with the airfoil in the 5°, 10°, and 15° slots in the Kelvin Lift & Drag Balance arm.

The Joule-Thomson apparatus (Leybold Didactic, Huerth, Germany) consisted of a glass cylinder with five outlets and a glass filter subdivision. One side of the division was connected to the helium or carbon dioxide gas pressure cylinder that was supplied in the laboratory, a pressure sensor, and a NiCr-Ni thermocouple, which measures the temperature inside that chamber. The other chamber contained outlets for another thermocouple and for the transferred gas. A temperature controlled water bath was used to set the system to the

The concept of boundary-layers was first thought of in the early 1900s by Ludwig Prandtl. He presented a paper in Germany in 1904 which outlined a slightly viscous fluid near a solid boundary cite{Prandtl}. In this paper certain assumptions were made. Firstly the Reynolds number is large, so the viscous terms can be neglected far away from the solid boundary. Then there exists a thin layer of fluid near the solid boundary and this fluid is known as a boundary-layer. Outside this viscous fluid is an inviscid fluid region, which gives rises to a multideck structure. This boundary-layer has a thickness of $delta$ and is proportional to Reynolds number by $delta/L propto {Re}^{-1/2}$, where $L$ is the characteristic length scale of the solid boundary. The pressure from outside the boundary-layer is not significantly different from the pressure inside the boundary-layer. The boundary condition for pressure can be approximated by the value of upper boundary in the inviscid region. Rescaling the wall normal coordinate $y$ by the boundary-layer thickness ${Re}^{-1/2}$ implies that we are located within the boundary-layer and this retains some viscous terms. The following scalings are introduced to perform analysis within a boundary-layer

‘Low speed streaks’ refer to the regions of relatively slow flow spaced out in a pronounced manner. They generally occur ‘between the legs of hairpin vortices, where flow is displaced upward from the surfaces so that it convects low momentum fluid away from the wall.’[2]. Streaks have been found to occur in the sublayer region by Kline and Runstandler (1959)[1] and have been shown to occur at a distance of y+

The details of the CV system used in this work are described elsewhere [15,16]. The design of the downstream compartment allows varying the volume for gas accumulation from 77.6×10-6 m3 to 1009.7×10-6 m3; at the same time, the effects of resistance to gas accumulation reported in ref. [31-33] are minimized. The absolute pressure transducer (MKS model 627B11TBC1B) to monitor gas accumulation operates in a range of 0 to 1333 Pa (10 torr), with an accuracy of 0.0133 Pa (0.0001 torr) and a maximum error of 0.12% of the pressure reading. This level of precision is typical of the best precision from pressure transducers currently available on the market. Prior to each experiment, the system is evacuated using a rotary vacuum pump (Edwards model RV3) for at least 48 h, and just before the experiment, leak tests for both upstream and downstream sides of the membrane are performed. During the leak tests, the vacuum pump is disconnected from the system and gas accumulation (if any) in the downstream reservoir is monitored for a period of time (from 20 minutes to 1 hour depending on the duration of the experiment).

“This 1.5 stage low speed facility operated from laboratory air conditions at about 1 atm inlet

A detailed study of secondary flows and separation in S- duct diffusers, their detection and control was done. The experimental investigations were also studied given in various references. The experiments were carried out with and without inflow distortion. The subject over which the flow is visualized is an S-Duct diffuser which is an essential feature of a combat aircraft inlet system. Due to space limitations, a short duct is required, resulting in high center-line curvatures. Due to centerline curvature, there are cross-stream pressure gradients giving rise to secondary flows. Control of secondary flows and separation has been explored by a number of investigators. Guo and Seddon investigated the swirl in an S-

For wind engineering applications and simulation of flow around buildings, the validation can be defined into two main phases, including: (1) wind flow characteristics validation; and, (2) validation of simulated pressures on surfaces of building [99]. In this chapter, the CFD LES is carried out to simulate the inflow turbulence content in such a way to compensate the lack of large eddies in the flow. The generated transient inflow should possess natural wind characteristics with both time (temporal) and space (spatial) correlations.

Boundary layers are thin regions next to the wall in the flow where viscous forces are important. The above-mentioned wall can be in various geometrical shapes. Blasius [1] studied the simplest boundary layer over a flat plate. He employed a similarity transformation which reduces the partial differential boundary layer equations to a nonlinear third-order ordinary differential one before solving it analytically. The boundary layer flow over a moving plate in a viscous fluid has been considered by Klemp and Acrivos [2], Hussaini et al. [3], Fang and Zhang [4] and recently Ishak et al. [5] and Cortell[6] which is an extension of the flow over a static plate considered by Blasius. A large amount of literatures on this problem has been cited

The outer part of boundary layer area can be assumed inviscid like before Prandtl. The boundary layer is a very thin layer around the solid body. Prandtl explained the boundary layer with the help of adhesion. The velocity difference between solid body and fluid is zero, in the other words there is no slip condition in between since, they are interlocked by adhesion. In the light of this information, the velocity gradient of flow changes from the surface of solid body to the outer line of boundary layer, and this means shear stress demonstrates a vast alteration. Therefore, the friction drag force that observed on the surface of solid body cannot be ignored.[5]

Intake Tunnel: A circular Intake Tunnel of 7.2 m finished dia with 50 cm R.C.C lining is proposed, considering 4 m/s limiting velocity. Length of intake tunnel is proposed as 227 m with radius of curvature 70 m at the junction with intake structure. A bed slope of 1:100 is provided.