Pressure probes

Introduction:

Pressure investigations employs the force per unit area measured at the flow speed which have been employed to specify fluid flows and mensurating mean or mean speed is to utilize a Pitot inactive tubing. Pressure investigations can be used step the stagnancy force per unit area, the inactive force per unit area, and the flow angle within a unstable watercourse. When planing a pneumatic investigation that is to be used in flow measurings, the effects of obstruction, frequence response, force per unit area hole size and geometry, the local Mach and Reynolds Numberss and the comparative graduated table of the phenomena under probe must be addressed. In general, better truth is gettable if smaller investigation and transducers are used though this normally means that the mechanical unity may be compromised, that the response times are longer and that there are greater jobs with taint in soiled environments. The effects of obstruction become greatest when the flow is compressible. For illustration, infixing a investigation into a gas watercourse where the undisturbed Mach figure is 0.9 will do the flow to choke if the flow country is reduced by merely 1 per centum. In supersonic flow, a investigation root can make a degage bow daze that lies far upstream of the investigation tip.

Chu and Young originally proposed and demonstrated the usage of consecutive tubing with its terminal cut at an oblique angle to the tubing axis applied to a survey of the flow near a wing organic structure junction. Chu ‘s process requires measuring of the force per unit area at a series of four angles of the tubing axis ( roll angles ) for every 90° intervals and besides employed the usage of a square-cut sliding screen was extended over the rotatable to supply 5th force per unit area measuring.

Explicit standardization of the consecutive tubing required adjustment of the response to several multinomials and involves tonss of standardization invariables. The five force per unit area measurings are used to use five-hole investigation to find speed magnitude and way. Bryer and Pankhurst supply a good sum-up of truth punishments incurred for misalignment for different Pitot inactive tubing design. Dynamic and Static force per unit areas are required for complex flows and it ‘s achieved by multi-hole force per unit area investigation which typically requires standardization. Each mensural force per unit area for rotary motions of the tubing was obtained from one of the four circumferential holes of a 5-hole investigation and force per unit area measured with the screen extended was used from the cardinal hole of a 5-hole investigation.

Straight tubing with oblique cut terminal have many possible advantages when compared to multi-hole investigations and most obvious may be its size for a given tubing diameter, a five hole investigation would show 5 times the cross-sectional country. The chief motive for the original development of the individual hole investigation was that it does non affect the usage of spatially separated measuring holes, which will do a false measuring of the flow angle in flows where spacial gradients of speed magnitude are encountered. In malice of this of import advantage, they do n’t look to hold any development or application of the investigation aside from Chu ‘s. It seems likely of mechanical complexness involved in the mechanisms requires a axial rotation placement and screen extension has discouraged farther development. The force per unit area response is besides less sensitive with the individual hole investigation for a given cut angle as compared to that of a individual port on a five hole investigation.

Rotatable individual hole force per unit area investigation is developed utilizing a hallow shaft stepping motor for axial rotation placement is shown in fig.2.

The mechanical design of the axial rotation thrust, the issue of sealing and form of the sliding screen and most late is the force per unit area response of the angle-cut tubing for incompressible flow of changing magnitude and way. The investigation ‘s axial rotation mechanism is automatically simpler than Chu ‘s and provides axial rotation positioning in 15° increases. Chu ‘s attack of graduating and utilizing the devices as it were a 5-hole investigation was abandoned: it was found that the particular symmetricalness of the device can be exploited to give a standardization map with 6 grades of freedom. The standardization of the rotatable investigation ‘s response in this mode does non necessitate a force per unit area measured by a square-cut sliding screen. The square-cut tubing force per unit area measuring is still required in these instances where the inactive force per unit area is to be determined and for these state of affairss we have obtained extra measuring utilizing a wholly separate, non-rotatable, square-cut entire force per unit area investigation.

The application of the graduated investigation to measurement in a flow of unknown speed magnitude and way has besides been re-examined.A

PROBE DESIGN:

The new response map has been incorporated into a new flexible, inexplicit attack to treat force per unit area measurings made at more than 4 consecutive axial rotation angles if desired to better accuracy.A Initial trials of the full process employed a paradigm 1.3 millimeter diameter, 45 degree-cut-angle investigation without a skiding screen to mensurate the speed profile in a planar disruptive boundary layer.A Roll placement was accomplished by a sub illumination, hollow shaft stepping motorA?a immense betterment allowed by modern promotions in stepping motor technology.A In these trials, speed magnitude agreed with that measured by a conventional square-cut entire force per unit area investigation to within 0.5 % of the watercourse velocity, and flow angle was within 1 grade of expected values. The present work was conceived to widen the rating to a 3-dimensional flow with small-scale characteristics including inactive force per unit area fluctuation.

Theoretical analysis methods:

It would be advantageous if the standardization features and response of a Single-hole investigation could be determined by analytical processs. In fact, there are methods that can assist to confront up the analysis of force per unit area investigations from a theoretical point of view. Some of these methods are:

– The streamline projection method

– The possible flow solution

For trapezoidal or cobra shaped caput investigations, analytical processs of any type are hard. These complex geometries, characterized by disconnected alterations in contour, are capable to flux separation and syrupy effects that are non modelled by current computational techniques. However, the streamline projection method is used in add-on to the experimental research every bit good as the computational probes. It will be shown that this simple method can easy foretell the single-hole investigation standardization coefficients, at least qualitatively.

For investigations of easy contour geometry, ( e.g. , cylindrical investigation caput ) , the streamline projection method is valid, but a possible flow solution can besides foretell the force per unit area distribution and the corresponding standardization features to a sensible truth.

While the analytic relationships are valuable for word picture of investigation behavior and as a usher to the functional signifier of standardization equations, it is improbable that they are capable of replacing single investigation standardizations. This is due to both the restrictions of the derivation every bit good as the fabrication abnormalities of the investigations. Regardless of the truth of the theoretical derivations, the latter effects may ever ask single investigation standardizations, peculiarly for little sized investigations.

Measurement of informations and development of an insertion process for the information analysis become duty of the investigation user.

CALIBRATION TECHNIQUES:

For both, standardization and application, the investigation ‘s mention line is defined by some consistent feature of the investigation ‘s geometry. In application, a mention way obtained by puting P1 with P2 is non ever meaningful, since ab initio a known flow way would be required to associate the balanced status to an absolute spacial mention.

The investigation can be operated in two ways:

  1. Nulling technique
  2. Stationary method ( non-nulling technique )

Both methods offer advantages and disadvantages. Due to infinite limitations in turbo machinery applications and weave tunnel obstruction, the investigation is frequently required to be little, and the trouble associated with traversing and informations acquisition encountered when the investigation is used in a nulling manner, do a non-nulling method a better option.

Calibration maps are so used to happen the flow angles. The watercourse atmospherics and entire force per unit areas – and, therefore, Mach figure – can be determined in similar mode.

NULLING Technique:

The nulling technique is the most accurate but automatically complex. It is the most simple in footings of informations analysis, every bit good. The investigation is mounted on a three grade of freedom tracking system and is oriented such that the X-axis is parallel to the flow ( yaw and pitch angles are both zero ) . The halfway force per unit area pat measures the stagnancy force per unit area P1 and the force per unit areas in the two outer tubings are equal ( P2=P3 ) and relative to the inactive force per unit area. Finally, the investigation place is noted and the flow way is determined from a calibrated graduated table.

This nulling technique requires a really sophisticated traversing system and long informations acquisition clip, since the investigation must be yawed at each measuring location until the two force per unit areas are equal. This can take a long clip, particularly if the investigation is little and has a slow clip response.

If infinite restrictions or other considerations make nulling techniques impractical, three-hole investigations in a non-nulling manner can be employed for measurings in low velocity, incompressible flows.

STATIONARY METHOD:

The stationary method or non-nulling technique tends to be less accurate but offers simpleness in installing. The latter feature is the most of import in turbo machine applications.

It is performed by puting the investigation at changeless pitch and swerve values with regard to the trial subdivision. The three force per unit areas are measured at each measuring location by tracking the investigation over the flow field. From these three measured force per unit areas, the way and magnitude of the flow with regard to the X-axis of the force per unit area investigation are determined.

Although elegant in its simpleness, this technique encounters uniqueness when standardization for big angle of swerve is sought. So it is restricted to take down flow angle ranges, forestalling its usage in extremely 3D flows.

ENERGY BERNOULLI EQUATION:

The flow gesture is known to be a map of several non-dimensional parametric quantities. The most of import 1s in aeromechanicss are:

Reynolds figure:

Mach figure:

Gass at low speed – the standardization experiments are conducted at Ma & lt ; 0.2 – can be considered as basically incompressible ( constant-density ) fluids. The analysis of the steady flow for this kind of fluid starts with the preservation of mass, impulse and energy.

For unidimensional flow along a watercourse tubing ( Fig. 1 ) , the mass preservation equation for steady flow has the signifier:

If it is further assumed that the flow is in viscid, the impulse equation is:

The cross subdivision of the watercourse tubing must be little in order to see the local values of the force per unit area and speed.

For the steady province, the last term in Eq. ( 4 ) drops out, and the equation can be integrated along the way s of the watercourse tubing, to ensue in the Bernoulli preservation equation for energy:

The force per unit area pin Eq. ( 5 ) is the inactive force per unit area. It is the constituent of the force per unit area that represents unstable hydrostatic effects. And in rule, it is measured by an instrument that moves along with the fluid. This is, nevertheless, inconvenient, and the force per unit area is normally measured via a little hole in a wall arranged so that it does non upset the flow. The measure is normally called dynamic force per unit area. It is the constituent of the fluid that represents unstable kinetic energy.

Entire force per unit area platinum, sometimes besides called “stagnation pressure” , is defined as the force per unit area that would be reached if the local flow is imagined to decelerate down to zero speed, frictionless. Entire force per unit area is the amount of inactive and dynamic force per unit area:

From measurings of the sum and inactive force per unit areas, the speed can be obtained as,

This follows readily from Eq

For Eq. ( 6 ) and ( 7 ) to use, the investigation must non upset the flow, and it must be carefully aligned analogue to the watercourse. A A A A A

DEFINITION OF HOLE AND CALIBRATION COEFFICIENTS:

The force per unit area sensed by the hole idiffer from the free watercourse inactive force per unit area p. The hole coefficient qi is normally used in the undermentioned signifier:

Where irepresents figure of holes.

It is evident that the standardization features must include informations that represent force per unit area differences in the swerve plane every bit good as differences between the measured and the true, local sum and inactive force per unit areas. When the investigation is used to mensurate these measures, the relationship between them and the swerve angle I”I? is described by the standardization coefficients. These force per unit area coefficients must be defined so that they are independent of speed and are a map merely of the flow angular shape.

Entire force per unit area coefficient:

Inactive force per unit area coefficient:

Consequence OF TURBULENCE ON PRESSURE PROBE:

The single-hole swerve metre:

This device is a individual chamfered tubing over which can be skid a arm which, in its forward place, converts the device into a pitot tubing. The Pitot force per unit area holding been measured, swerves and pitch angles can be deduced from readings of the individual chamfered tubing at, at most, four azimuthal places. The yaw standardization in unvarying flow is shown in figure 13 ( a ) , and, unlike the conventional three-hole swerve metre but like the Gupta swerve metre, breaks downward from a additive fluctuation at a yaw angle of about 15 ” . In disruptive flow, nevertheless, the yaw standardization interruptions upwards from the additive part at an angle of about 20 ” . The incline of the additive part is about 2 % greater in turbulent flow than in unvarying flow.

PRESSURE PROBE MEASUREMENTS:

The standard method for mensurating mean and mean speed is to utilize a Pitot inactive tubing. Accurate usage of this investigation relies on alining the investigation to cognize primary flow way. Chu, Bryer and Pankhurst supply a good sum-up of the truth punishments incurred for misalignment for different Pitot – inactive tubing designs. For complex flows, both dynamic and inactive force per unit areas are required every bit good as flow way. This is most normally achieved by utilizing combination or multi-hole force per unit area investigation which typically requires standardization in known flow conditions representative of those in which they will be used.

Many different types of investigations have been proposed in the yesteryear, either for mensurating flow way, flow velocity or both. In truths due to Reynolds-number effects can be important and need to be considered for accurate measurings. Westphal developed a individual hole investigation in which a individual tubing cut at 45° is rotated about its axis by a illumination hoofer motor. This allows speed, magnitude and angle measurings with a significantly smaller investigation, although the measurement process.

When utilizing multi-hole investigations, one issue which should ever be kept in head is that ultimate truth of the force per unit area investigation relies on the truth of the standardization. Furthermore, one uncertainness that remains with most go outing standardization techniques is that the standardizations are performed at steady pitch and swerve angles in uniform, and no history of the nonlinear effects of the turbulent flow are accounted. The degree of this uncertainness remains ill-defined.

In order to utilize a individual hole force per unit area investigation in a “ non-nulling ” manner, it is necessary to happen a relationship between the angle and the speed of the flow, the inactive force per unit area and the force per unit areas measured in the investigation holes. Such a relationship is obtained by agencies of a direct standardization of the investigation. Practically, all the methods that can be found in the literature sing the standardization process of multi hole force per unit area investigations [ 8 ] have a common characteristic: they use normalized standardization coefficients. Such coefficients, as defined in [ 9 ] , are obtained for a three-hole investigation as a map of the entire force per unit area, P0, the inactive force per unit area, PS, and all the force per unit areas measured in the cardinal hole, Personal computer, and in both left-hand side, PL, and right-hand side holes, PR, giving up:

Where CI± represents the angular coefficient, CP0 and CPs are the entire and inactive force per unit area coefficients and Q is the standardization factor that is introduced in all the coefficients. All the coefficients become independent of the dynamic force per unit area if normalized with the factor Q. Thus, the angular coefficient is merely a map of the flow angle, so both inactive and entire force per unit area coefficients provide the speed magnitude and the inactive force per unit area in the flow. The standardization apparatus of a investigation is based on a shifting sequence of the investigation inside a known flow field. This means that the comparative angle place of the investigation regard to the flow way has to be increasingly modified utilizing a highly-precise angular stepping mechanism. For every angular place, the sum and inactive force per unit areas every bit good as all the force per unit area measurings in the holes are stored. Using these force per unit area values, all the standardization coefficients defined in ( 1 ) are straight obtained. Since the investigation is symmetric, it is possible to carry through the standardization merely sing positive ( or negative ) incidence angles of the flow. However, in order to avoid little differences derived from imperfectnesss of the investigation during the fabrication procedure, it is preferred to carry on a complete standardization apparatus. The standardization coefficients to be obtained following ( 1 ) and the process to find both speed magnitude and way of the flow after finishing a measuring sequence with a CTHP is sketched in Fig. 3. The standardization provides the fluctuations of the coefficients CI± , CP0 and CPs with the flow angle I± . Then, the angular coefficient is obtained from the different force per unit areas sensed in the holes when mensurating. Once the angular coefficient CI± is calculated, the flow angle is known and the values of both force per unit area coefficients, CP0 and CPs are besides determined. These coefficients allow us to cipher both inactive and entire force per unit areas of the flow. The difference between them, i.e. the dynamic force per unit area, is instantly related to the speed magnitude of the flow.

The chief end is placed on the development of general relationships to cut down the numerical computations that are necessary in the post-processing. However, due to the betterment of the computational resources in recent old ages, nowadays it is better to use insertion.

Typical job that arises in the standardization with the factor Q is the debut of remarkable points for all standardization coefficients when Q turns to zero. In fact, the job is non truly associated to the visual aspect of remarkable points, which could be avoided easy by agencies of some sort of mathematical operator. The unequivocal job lies in the non-monotonous behavior of the curve of the angular coefficient when traversing from one side to the other side of the uniquenesss. The 2nd confining factor of the CTHP public presentation refers to the speed scope that is mensurable. Basically, the standardization method is based on the fact that when the standardization coefficients are normalized, they vary significantly with the flow incidence angle, but are practically independent of the flow speed [ 9 ] . The normalized standardization coefficients are obtained sing that the force per unit area distribution around a cylinder can be expressed as follows:

Where

Pd corresponds to the dynamic force per unit area

Cp is the force per unit area coefficient.

I? is the angle between every point in the cylinder surface and the free watercourse direction.A

In the instance of individual hole force per unit area investigation, with building angle I? , the force per unit area in hole at different angles is given by:

If all look above is introduced in the definition of the normalized standardization coefficients, it is easy demonstrated that the coefficient are independent of both entire and inactive force per unit area, being determined merely by the force per unit area coefficient Cp.

ANGULAR CALIBRATION:

This subdivision contains a theoretical analysis of the standardization coefficients in the instance of a CTHP ( which is similar to individual hole force per unit area investigation ) with an angular distance of 45 grades between the holes. The standardization coefficients that are obtained utilizing a traditional normalizing factor Q are compared to the new set of coefficients derived from an improved standardization factor QN. The distribution of the force per unit area coefficient Cp in the cardinal hole should be obtained turn overing the investigation 360 grades about its ain axis in a flow field. However, since the involvement is now placed in developing a theoretical model of the standardization apparatus, the analysis is afforded utilizing bibliographic informations. Therefore, we have employed for convenience a curve suiting tool based on splines through the experimental informations collected in [ 16 ] for a ReynoldsA figure of 2.3A-104. The Cp distributions in both left ( L ) and right ( R ) holes have been constructed switching the original informations for the cardinal hole A±45° severally. The concluding distributions in the three-holes, which are a map of the flow angle I± , are plotted in Fig. 7. Though adapted from experimental consequences, Cp distributions imposed like this have to be considered as ideal, since these premises imply that there is no uncertainness associated either to the angular distance of the holes or to the investigation misalignment. As expected, the upper limit of the force per unit area coefficient in the cardinal port is obtained for a flow angle of 0 grades. Similarly, maximal values for both left and right ports are reached severally at A±45° . If the building angle of the investigation would be 60 grades, so the maximal values for both sidelong holes would be placed at A±60° . Following, with the distributions of the force per unit area coefficient of Fig. 7, the standardization coefficients that are derived from the traditional standardization ( normalization factor Q ) are shown in Fig. 8. The entire and inactive force per unit area coefficients, CP0 and CPs, are really similar. Both of them are symmetric regard to an incidence flow angle of 0 grades. In the angular scope of A±30° are positive, demoing values between 0 and 4. For the angular scope of A±10° are about changeless, lifting as the flow angle additions towards A±30° . On the contrary, the angular coefficient C_ is anti-symmetric regard to a flow angle of 0 grades. This manner, it takes positive values for negative incidence angles and negative values for positive incidence angles, ranged from -6 to 6. At a 0 grade flow angle, the angular coefficient is zero. The significance of Fig. 8 is that the angular scope of a CTHP calibrated with the traditional method is merely limited to the interval between -30 and 30 grades. Outside of this angular scope, the angular coefficient is no longer humdrum with the flow angle, as illustrated in Fig. 9. Shown in the figure is the distribution of the angular coefficient calculated with the regular standardization factor Q, for two investigations with building angles of 45 ( black line ) and 60 grades ( grey line ) . The x-axis has been extended to include an angular scope of A±70° .

Notice that outside the interval of [ -30° , +30° ] , remarkable points are presenting crisp discontinuities in the coefficient. As a consequence, beyond the internal angular scope, the standardization informations can non be reduced to obtain a alone flow angle, restricting the usage of the investigation. In add-on, as observed in Fig. 9, both investigations with different building angles exhibit a similar come-at-able angular scope. As a effect of this consequence, an effort was made to convey out a new method to graduate a CTHP, with the concluding aim of increasing the angular scope of the investigation. By definition, the angular coefficient is calculated as the force per unit area derived function on the left and right holes, divided by the standardization factor Eq. ( 1 ) . If the standardization factor would be value integrity, the force per unit area derived function between ports L and R would offer a humdrum angular coefficient along an angular scope of, at least, twice the building angle of the investigation ( see Fig. 7 ) . With that force per unit area derived function in the numerator of the angular coefficient, it was necessary to happen a standardization factor every bit changeless as possible when changing the flow angle. This new standardization factor is labelled as QN.

The force per unit area distribution in the hole is rather similar to the inviscid behavior of possible flow ( see Fig. 4 ) , so it could be expressed as a map of cos2I± . The force per unit area distribution in R is obtained traveling the cardinal distribution an angular distance equal to the building angle of the investigation. As a effect, it could be expressed as a map of sin2I± . However, the aim is to happen an approximative relationship between the force per unit area ports, instead than an exact mathematical look. Then, since cos2I± + sin2I±=1, the new standardization factor QN could be defined as the amount of both force per unit areas in C and R. On the other manus, QN must be independent of the inactive force per unit area. Sing that the force per unit area in L is about changeless for positive flow angles, it is executable to deduct twice the amount of the force per unit areas in the cardinal and right holes in order to extinguish the inactive force per unit area in the definition of QN.

This definition provides a standardization factor, independent of the inactive force per unit area, which can be expressed as the merchandise of the dynamic force per unit area times a certain map of the flow angle. Therefore, by agencies of QN, an angular coefficient independent of the dynamic force per unit area and lone map of the flow angle is available. Previous treatment is entirely applicable for positive flow angles. In the instance of negative incidences, it is necessary to reconsider this logical thinking, so it can be deduced that the standardization factor should be now

In the standardization procedure, it is possible to specify different angular coefficients in instance of positive or negative flow angles, but when mensurating this favoritism is unpractical. For a existent measuring, you may hold different angular coefficients merely if you can distinguish the angular scope utilizing some of the force per unit area values sensed in the investigation holes. Fortunately, in the instance of the standardization factor QN defined through ( 5 ) and ( 6 ) , the flow angles are positive when PR & gt ; PL and negative when PL & gt ; PR. Even when the flow angle is zero, both force per unit areas in the left and right holes are the same, so QN nowadayss no discontinuities for I±=0° . In drumhead, the standardization factor QN is defined as:

Uncertainty:

Having defined this new standardization method, it is necessary to analyse the uncertainness degrees associated to the standardization factor QN. Present probes confirm that non merely the angular scope is increased, but besides the uncertainness degrees are approximately different regard to typical uncertainness degrees associated to the traditional standardization. In many ways, the factor QN can be considered as two times the traditional factor Q, since it is calculated utilizing twice the force per unit area values of the holes. Then, the uncertainness of the measurings associated to the factor QN may be estimated someway as twice the uncertainness of the measurings obtained utilizing Q. Nevertheless, the uncertainness in the angular coefficient is little because of the decreased transportation of uncertainness in the mathematical procedure. In fact, though the uncertainness in the flow angle is higher ( shown subsequently ) for little flow angles, the uncertainness in the speed magnitude and the inactive force per unit area are lower, even inside the typical angular scope of traditional standardization ( between A±10° and A±30° ) . The methodological analysis proposed has been followed to measure the uncertainness of the flow variables measured with a individual hole force per unit area investigation. Harmonizing to old distributions of the angular coefficient, the flow angle can be expressed in footings of a alone expressed analytic map of CI± . Hence, the uncertainness of the flow angle is:

Using the definition of the angular coefficient in ( 1 ) , the uncertainness of CI± can be besides obtained following an correspondent algebra:

Where Q is the traditional standardization factor. To that terminal, it has been supposed that the uncertainness in the force per unit area is the same for all the holes, being equal to the uncertainness in a force per unit area measuring, IP, which – in a typical experiment – is fundamentally determined by the uncertainness of the force per unit area transducers.

The uncertainness of the traditional standardization factor Q is given by:

Substituting Eq. ( 10 ) into ( 9 ) , the uncertainness of the angular coefficient is expressed as a map of the uncertainness in the force per unit area measuring:

Finally, including Eq. ( 11 ) in ( 8 ) , the uncertainness of the flow angle is:

Where the derived function of the angle with regard to the angular coefficient must be evaluated numerically. Analogous considerations lead to specify the comparative uncertainness for the speed magnitude every bit good as the inactive force per unit area uncertainness, harmonizing to:

Using indistinguishable tax write-offs in the instance of the new standardization method, the uncertainness of the standardization factor QN is:

From ( 15 ) , the uncertainness associated to the flow angle, the comparative uncertainness for the speed magnitude and the inactive force per unit area uncertainness for the new standardization are given by:

The right column of Fig. 12 shows the distribution of all the uncertainnesss formulated earlier as a map of the flow angle. Both consequences for traditional ( dotted lines ) and new ( solid lines ) standardizations are included in the array of secret plans. In add-on, the left column of the figure reproduces the standardization coefficients that are derived from both normalization factors Q and QN. All the uncertainnesss have been made non-dimensional. The uncertainness of the flow angle is expressed as a per centum of the uncertainness in the force per unit area measuring, IP, comparative to the dynamic force per unit area Pd. This means that, for case, if I±=30° the uncertainness in the flow angle is about 0.5 grades for every 1 % of IP=Pd. The uncertainness for the inactive force per unit area is referenced to the uncertainness in the force per unit area measuring. Finally, the comparative uncertainness for the speed has

been made non-dimensional with the uncertainness in the force per unit area measuring relation to the dynamic force per unit area, alternatively of utilizing the inactive force per unit area. This implies that the inactive force per unit area of the flow can non be overly high with regard to the dynamic force per unit area.

From Fig. 12, it is observed a common characteristic for both standardizations: the uncertainness of the flow angle tends to infinite when the standardization factor tends to zero ( at A±30° for Q and A±70° for QN ) . This is because the angle uncertainness is calculated spliting by the standardization factor Eq. ( 12 ) and ( 16 ) . Alternatively, though the comparative uncertainness of the speed and the uncertainness of the inactive force per unit area are non obtained dividing by the standardization factor Eq. ( 13 ) , ( 14 ) , ( 17 ) and ( 18 ) _ , both variables tend to infinite at A±30° when utilizing the traditional standardization. This is a effect of the behavior of both inactive and entire force per unit area coefficients, which are besides infinite at A±30° ( left column of the figure ) . On the contrary, the comparative uncertainness of the speed and the uncertainness of the inactive force per unit area in instance of the new standardization are increased towards A±70° , but limited to finite values. For a flow angle of nothing grades, the uncertainness in the angle measuring is the same for both standardizations.

Inside the angular scope of A±30° , the uncertainness II± is somewhat higher when utilizing the new standardization than the traditional 1. Even so, at A±60° it is considerable little with merely 1 grade for every 1 % of IP=Pd. The comparative uncertainness in the speed magnitude and the uncertainness in the inactive force per unit area are a spot higher when graduating with QN for I± = 0° . On the other manus, in the angular intervals [ -30° , -10° ] and [ 10° , 30° ] , the consequences show a better public presentation of the new standardization method. Complementarily, the comparative uncertainness of speed takes values ranged between 0.5 and 1.2 times IP=Pd for the whole angular scope, which is an exceeding good consequence. The uncertainness of the inactive force per unit area is strongly increased from 1.2 to 2 times IP at A±40° , making up to 6 times IP when being nearby A±70° . Anyway, overall differences between the uncertainnesss evaluated for both standardization methods are non important in the angular scope of A±30° . Therefore, the new standardization is non merely supplying a CTHP that is capable of mensurating angular fluctuations of the flow up to 140 grades, but it besides presents sensible low uncertainnesss for the whole angular scope of the investigation ( A±70° ) .