Shock/Boundary Layer Interaction is unwanted phenomenon that occurs during the high velocity fluid flow. Recently developed fresh flow control device called micro-ramp ( portion of micro-vortex generator ) shown possible in commanding this job. Therefore, this research aims to analyze the capableness of micro-ramps in commanding SBLI under hypersonic status. Hypersonic is chosen because most of the old experiments are conducted under supersonic condition.A In this experiment, several theoretical accounts of micro-ramps will be placed under the hypersonic flow ( Mach 5 ) and oblique daze moving ridges will be generated. The flow feature recorded from Schlieren exposure will so be investigated.
Aim and Background
Hypersonic aircraft relies to a great extent on their air-breathing propulsion system. However, the beings of Shock/Boundary Layer Interaction ( SBLI ) during high velocity airflow critically lower the public presentation of the aircraft engine.
Shock/Boundary Layer Interaction ( SBLI ) is a natural phenomenon that is often a shaping characteristic in high velocity aerodynamic flow Fieldss. The interactions can be found in practical state of affairss, runing from transonic aircraft wings to hypersonic vehicles and engines. When daze wave interacts with boundary bed flow, like the figure below, diverse types of flow will happen such as the flow separation, unsteadiness, perpendicular flow, force per unit area moving ridges etc.
Picture recognition to H.D. Kim & A ; T.Setoguchi, “ Shock Induced Boundary Layer Separation ” , 8th International Symposium on Experimental & A ; Computational Aerothermodynamics of Internal Flow, Lyon, France, July-2007
The consequence of SBLI on external flow is that it increases the aerodynamic retarding force, which comparatively reduces the lift. It will besides bring on aerodynamic warming and increase instabilities such as recess bombilation and pounding. Meanwhile, for internal flow, it can do entire force per unit area loss, unsteadiness and loss of flow control public presentation.
There are several factors that influence this unwanted phenomenon. The factors include the flow Mach figure, Reynolds Number, Characteristic of Boundary bed Flow ( Laminar/Turbulent, Boundary layer thickness ) and flow geometry ( force per unit area gradient ) . As Mach figure additions, the lower limit of wall shear emphasis is decreased and it will make nothing at a point where a bantam separation bubble is formed. The more Mach figure additions, the more the bubble separation grows. SBLI cut down the quality of flow field by triping large-scale separation, doing the flow unsteady and distorted due to entire force per unit area loss, and more worst make an engine unable to get down. Most of the interactions are caused by oblique daze moving ridges, but the terminal interaction is usually due to a normal daze.
The traditional manner to command the SBLI ‘s effects is by a bleed technique, which removes low-momentum flow from the boundary bed utilizing suction through a porous surface on the recess wall. Although this technique reduces the characteristic effects on the boundary bed, bleed systems are heavy and complex, decrease mass flow to the engine and introduce extra retarding force. As a consequence, this bleed technique gives a really low efficiency. Therefore, many different types of whirl generators ( VGs ) have been proposed and investigated as possible replacings to shed blood systems.
Micro-ramp, a portion of micro-vortex generators is the fresh type of flow control device that can gives similar control benefits as the bleed technique but without bleed punishment. It has the ability to change the near-wall construction of compressible disruptive boundary beds to supply increased commixture of high velocity fluid which improves the boundary bed wellness when subjected to flux perturbation. Since their size is little, micro-ramp are embedded in the boundary bed which provide reduced retarding forces compared to the traditional whirl generators while they are cost-efficient and do non necessitate a power beginning.
The initial thought on utilizing micro-ramp as SBLI control device was proposed by Prof. Babinsky * [ 1 ] . They conducted experimental probes at Mach 2.5 based on the geometries of micro-ramp suggested by Anderson * [ 2 ] in their numerical optimisation surveies. From the experiment, they observed that micro-ramp produces a counter-rotating streamwise whirls fluxing downstream and this whirls helped to stamp down the SBLI ‘s consequence. This gesture transports the low-momentum flow at the wall surface to the outer parts of the boundary bed and at the same time brings the high-momentum flow from the outer parts towards the surface of the wall. As a consequence, more healthier and robust boundary bed was formed, which is less prone to flux separation.
Subsequently, the flow feature in the downstream part of the micro-ramp was produced in detailed by Li & A ; Liu * [ 3,4 ] , in their numerical probe. It was so identified that a concatenation of vortex pealing constructions originated from the vertex of the micro-ramp due to Kelvin-Helmhotz instability, and these constructions propagate farther downstream and interact with the encroaching daze moving ridge, finally falsifying the construction of the daze moving ridge hence cut downing its strength.
Until now, most surveies of micro-vortex generators in SBLI have been performed in simple flow-fields, such as the level home base normal or oblique SBLI and besides in supersonic status. Therefore, this research will concentrate on hypersonic status because there ‘s deficiency of research and cognition of MVG under this status. It is of import to research the ability of micro-ramp in commanding SBLI effects under hypersonic status and subsequently better the detached boundary bed caused by the incident daze.
The result of this research is of import to better the current apprehension and cognition on the efficiency of micro-ramps in hypersonic status. For this experiment, we will detect the behavior of the flow over and downstream the micro-ramps and its capableness in commanding SBLI consequence in a flow velocity of Mach 5.
Significant of Research
This research is important because it can demo us the ability of micro-ramps in commanding Shock/Boundary Layer Interaction. As mentioned before, the SBLI will do the flow field go unsteady and can take down the aircraft engine public presentation. It is necessary for applied scientists to minimise the effects of SBLI so that aircraft winging in hypersonic status do non hold degraded public presentation. This is really of import particularly for military/ jet combatant aircraft and outer infinite projectile which normally winging in hypersonic.
For this experiment, we need to hold the undermentioned technology/system to carry through our experiment outlook. The needed system/technology is as follow:
High Supersonic Wind Tunnel
High Supersonic Wind Tunnel is a air current tunnel that can bring forth hypersonic velocities ( Mach figure 5 to 15 ) . These types of tunnel must run intermittently with really high force per unit area ratios when initialising. Since there is temperature bead during spread outing flow, the air indoors have a possibilities to go liquified. Therefore, pre-heating must be applied and the nose may necessitate chilling. Shock tubing can be use to bring forth high force per unit area and temperature ratios.
( Definition of HSST, beginnings from: Wikipedia, Hypersonic air current tunnel, hypertext transfer protocol: //en.wikipedia.org/wiki/Hypersonic_wind_tunnel )
Figure: High Supersonic Wind Tunnel ( HSST )
Micro-ramps are parts of micro whirl generators, which is an aerodynamic surface with little vane that intended to bring forth whirl. Vortex generators can better the efficiencies of wings and control surfaces by detaining the flow separation and aerodynamic stalling.
In this experiment, two types of micro inclines theoretical account will be investigated. These two theoretical accounts can be differentiated by their height per centum from boundary bed thickness. The first theoretical account is MR70 ( the tallness is 70 % from boundary bed thickness ) and the following 1 is MR30 ( 30 % from boundary thickness ) . Boundary bed thickness is defined as the distance between the walls to the point where the speed of the flow becomes free watercourse speed. This boundary bed thickness can be identified from preliminary experiment by utilizing really fast Schlieren images. The boundary bed obtained for this experiment is about around 5.8 millimeter. Subsequently, we designed the micro-ramps based on the dimension proposed by Anderson, with the ratio given by w/h = 5.86 and c/h = 7.2. The micro ramps theoretical account dimensions will be stated in the tabular array below:
Chord, degree Celsius
Picture recognition Mohd R.Saad, Hossein Zare-Behtash, Azam Che-Idris and Konstantinos Kontis, “ Micro-Ramps for Hypersonic Flow Control ” , Micromachines
Toepler ‘s z-type Schlieren system
Schlieren image is used to visual the flow of fluids of changing denseness around the experimented object. The construct behind this system is that the visible radiation from a individual collimated beginning reflecting on a mark object. Subsequently, the collimated visible radiation beam will be distorted due to the fluctuations in refractile index of denseness gradient existed in the fluid. This deformation creates a spacial fluctuation in the strength of the visible radiation, which can be visualized straight with a radiogram system.
This system is provided in many research lab, for illustration in Aero-Physics Laboratory in University of Manchester, which consist of a uninterrupted visible radiation beginning with a focussing lens and broad slit, 2 parabolic silver coated mirrors, a knife-edge and macro lens used for concentrating purposed.
Life-size image ( 20 K )
Picture taken from: ScienceDirect, Optics & A ; Laser Technology, “ Temperature measuring of air convection utilizing Schlieren system ” , hypertext transfer protocol: //www.sciencedirect.com/science/article/pii/S0030399208001357
IR Thermography can be used to observe radiation in the infrared scope of the electromagnetic spectrum and expose the images of that radiation. From Black Body Radiation Law, which stated that all objects above absolute nothing will breathe infrared radiation, it is possible for us to see one ‘s environment with or without seeable light by utilizing thermography. Since radiation additions when temperature additions, we can see the fluctuation in temperature utilizing thermography.
For this experiment, we will be utilizing FLIR Thermacam SC 3000 Cooled System. With the temperature scope sensing of -250K to 1,730K and sensitiveness of A±2 % , this camera is really suited for any experiment under hypersonic status. The recording frequence is 50Hz and added with Cooling system allows it to be cooled to 70K within 6 proceedingss or less.
ThermaCAMA® SC 3000 Infrared Camera
FLIR ThermaCAM SC 3000 Infrared Camera, “ hypertext transfer protocol: //www.iard.co.il/cubi/Cameras_brief.html ”
Since most of the fluids are crystalline, we can utilize flow visual image method to do the unseeable flow become seeable. For this experiment, we will be utilizing surface flow visual image. This method reveals the streamlines of flow in the bound as a solid surface is approached. Coloured oil flows are used to visualise the flow. The oil that we will be utilizing will be the standard 40W treated with a fluorescent dye or pigment. As the air flows over the theoretical account, the oil is carried downstream in a long run. Surface oil flows will bespeak the boundary of a flow separation since the oil can non perforate the separation boundary. Treated the surface oil with napthalin can assist find the passage point on the theoretical account as oil downstream of the passage point will be swept off.
For this experiment, it is necessary to bring forth oblique daze moving ridges to detect the effects of micro-ramps in commanding SBLI. Thus, daze generator will be used to bring forth oblique daze moving ridges on the theoretical account.
First, the status of HSST environment demands to be set up so that it has the flow velocity of Mach 5 ( with a Reynolds Number of 1,320,000 ) . The operational stagnancy force per unit area and temperature will be set to 650 kPa and 375K severally. The premise we made here is that the fluctuation of freestream Reynolds figure is really little. Therefore, we can handle the flow as the uninterrupted medium.
Next, the micro incline theoretical accounts will be mounted on top of aluminium metal level home base with this dimension: 300mm long, 50 millimeter broad and 5 millimeter midst. From the Toepler ‘s z-type Shlieren system, a Photron APX-RS high velocity picture camera will be used for high-velocity recording at 10,000 Federal Protective Service.
Meanwhile, the thermacam for our infra-red thermography will be mounted on top of the trial subdivision at a certain angle from perpendicular plane, and it is connected to a Personal computer for image storage.
For the oil surface flow visual image, the oil is applied during the air current tunnel is stopped. After the tunnel is operated to its coveted status, we let it run until the surface oil flow runs are decently established. Then the tunnel will be stopped and person demands to rapidly take the image of the runs. The thickness of the oil applied must be right so that the generated runs length produced will be meaningful. In order to increase the contrast between home base and the fluorescent oil, the level home base and the micro-ramps will be painted with black coloring material. Shock generators will be placed on top of the home base to bring forth oblique daze moving ridges on the micro-ramps theoretical accounts.
For two different theoretical accounts of micro-ramps and one baseline theoretical account ( without a micro-ramp ) , the Schlieren images, thermic image and surface flow visual image images for each of them will be collected at the terminal of the experiment. The consequences obtained will so be analyzed and discussed.
Model set-up, etc
( Material cost & A ; fabricating procedure )
( Provided in most of the lab )
$ 50 ( rent )
Fluorescent oil, napthaline
Based on the proposed timeline and cost, we can see that this experiment is rather executable. The estimated continuance for this experiment is about a hebdomad, which is sensible. The one twenty-four hours on readying is needed to acquire the general thought on how the experiment will be conducted. Then, more clip should be spend on puting up the research lab and tools required for the experiment. Micro-ramp can be manufactured by utilizing mechanical machine ( guided by an expert ) . This is of import phase as we do n’t desire our theoretical account to hold any surface mistake, which can impact the result of the experiment. Preliminary experiment is of import so that we can hold some expected consequence for our existent experiment. Two experiments are plenty to acquire the mean consequences.
In term of cost, some of the stuffs have been provided by the research lab. For thermaCAM, the existent cost for purchasing a new one is rather expensive. Therefore, leasing it will be a better pick.
From the analysis of the old researches, we can hold some outlook on what would be observed at the terminal of the experiment. First, there will be a seeable strong daze moving ridge which can be seen arising from micro-ramp taking border and a weaker daze moving ridge at the draging border of the theoretical account. Since the exposure clip in normal schlieren is excessively long, the incoming boundary bed can merely been seen in high-velocity schlieren exposure.
Next, the daze constructions between two theoretical accounts are non excessively distinguishable but thicker daze line can be observed merely at the draging border of thicker theoretical account ( in this experiment, it is on MR 70 ) . A bigger theoretical account besides will be expected to debar more flow due to its larger surface country, which requires stronger daze.
From the surface visual image, we expect to see some heavy accretion of oil at the micro-ramp ‘s prima border, which indicates the flow separation. At the downstream of the theoretical account, there will be a trail of primary whirls which can be determined by an country that is non covered with oil. It is because whirls gestures prevent the accretion of oil on the surface.
Chronology of surface oil-flow experiment ( Picture taken from Mohd R.Saad, Hossein Zare-Behtash, Azam Che-Idris and Konstantinos Kontis, “ Micro-Ramps for Hypersonic Flow Control ” , Micromachines )
Another expected observation is that the secondary whirls will look bigger near the centreline and at the downstream of the theoretical account will hold a larger wake country.
The infra-red thermic imagination of the surface temperature for both theoretical accounts besides can look into the behavior of the primary and secondary whirls.
Impact of research
The consequence of the experiment can assist better our cognition about the relationship and ability of the micro-ramp as a flow control device in commanding SBLI ‘s effects under hypersonic status. Practical usage of micro-ramp on hypersonic aircraft or engine can greatly cut down the aerodynamic loss, increase the overall public presentation and understate the energy loss. It is besides environmental-friendly device as it is merely a simple mechanical device without any usage of energy/chemical. Since the energy loss is minimise, less fuel ingestion will be needed to run the aircraft therefore cut down the operational cost.
Mohd R.Saad, Hossein Zare-Behtash, Azam Che-Idris and Konstantinos Kontis, “ Micro-Ramps for Hypersonic Flow Control ” , Micromachines, Published on 26th April 2012
Sang Lee, Large Eddy Simulation of Shock Boundary Layer Interaction Control Using Micro-Vortex Generators, University of Illinois, 2009
Qin Li and Chaoqun Liu, Implicit LES for Supersonic Microramp Vortex Generator: New Discoveries and New Mechanisms, Modelling and Simulation in Engineering Volume 2011 ( 2011 ) , Article ID 934982, 15 pages doi:10.1155/2011/934982, Accepted 12th January 2011, distributed under the Creative Commons Attribution License.
Holger Babinsky, AFRL-AFOSR-UK-TR-2011-0014 Shock Boundary Layer Interaction Flow Control with Micro Vortex Generators, May 2011, University of Cambridge Engineering Department
Lapsa, Andrew P, Experimental Study of Passive Ramps for Control of Shock-Boundary Layer Interactions, Issue Date 2009
Micro-ramp Flow Control for Oblique Shock Interactions: Comparisons of Computational and Experimental Data, Stefanie M.Hirt ( NASA Glenn Research Center ) , David B. Reich ( University of Florida ) , Michael B. O’Connor ( University of Notre Dame ) .