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Normal Shock Relationships

Fluid Mechanics · FE Reference Handbook section

Fluid Mechanics
12 formulas
10 exam-style examples
~60 min
All Fluid Mechanics lectures

Handbook notes for this section

Definitions and conditions exactly as the handbook states them.

  • A normal shock wave is a physical mechanism that slows a flow from supersonic to subsonic. It occurs over an infinitesimal
  • distance. The flow upstream of a normal shock wave is always supersonic and the flow downstream is always subsonic as
  • The following equations relate downstream flow conditions to upstream flow conditions for a normal shock wave.

Core formulas for this FE topic

Definitions, applicability, units, assumptions and worked examples for each relation.

Worked exam-style examples

The four ways this section is written on the real exam — thoughts first, then equations, then substitution.

Example 1
Normal shock relationships — solve for downstream Mach number — Normal Shock Relationships

normal shock relationships in a supersonic wind tunnel diffuser Given upstream Mach number (M_1) = 2.4000; specific heat ratio (k) = 1.3600, determine the downstream Mach number (M_2).

Given

  • upstreamMachnumber(M1)=2.4000upstream Mach number (M_1) = 2.4000
  • specificheatratio(k)=1.3600specific heat ratio (k) = 1.3600

Find

downstream Mach number (M_2)

Start with the thinking

  • The governing relation printed in this handbook section is Normal shock relationships.
  • Everything except M_2 is given, so isolate M_2 symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Normal shock relationships give the downstream Mach number for supersonic flow crossing a normal shock.

Step-by-step solution

  1. Step 1 — State the governing relation:

    M22=M12+2k−12kk−1M12−1M_2^2 = \dfrac{M_1^2 + \dfrac{2}{k-1}}{\dfrac{2k}{k-1}M_1^2 - 1}
  2. Step 2 — Rearrange the relation so that M_2 stands alone on the left-hand side.

  3. Step 3 — List the givens: upstream Mach number (M_1) = 2.4000, specific heat ratio (k) = 1.3600.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    M2=0.5159M_{2} = 0.5159
  6. Step 6 — Check: returning M_2 = 0.5159 to

    M22=M12+2k−12kk−1M12−1M_2^2 = \dfrac{M_1^2 + \dfrac{2}{k-1}}{\dfrac{2k}{k-1}M_1^2 - 1}

    reproduces the given quantities, and both sides carry the same units.

Answer:
M2=0.5159M_{2} = 0.5159

Why the other options are there

  • 1.0317 — kept a factor of two that cancels in the correct rearrangement.
  • 0.2579 — dropped that same factor in the other direction.
  • 0.5675 — rounded an intermediate value before the final step.

Reference: FE Handbook — Normal Shock Relationships

Example 2
Normal shock relationships — solve for downstream Mach number (case 2) — Normal Shock Relationships (2)

normal shock relationships ahead of a blunt body in supersonic flow Given upstream Mach number (M_1) = 1.2500; specific heat ratio (k) = 1.3800, determine the downstream Mach number (M_2).

Given

  • upstreamMachnumber(M1)=1.2500upstream Mach number (M_1) = 1.2500
  • specificheatratio(k)=1.3800specific heat ratio (k) = 1.3800

Find

downstream Mach number (M_2)

Start with the thinking

  • The governing relation printed in this handbook section is Normal shock relationships.
  • Everything except M_2 is given, so isolate M_2 symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Normal shock relationships give the downstream Mach number for supersonic flow crossing a normal shock.

Step-by-step solution

  1. Step 1 — State the governing relation:

    M22=M12+2k−12kk−1M12−1M_2^2 = \dfrac{M_1^2 + \dfrac{2}{k-1}}{\dfrac{2k}{k-1}M_1^2 - 1}
  2. Step 2 — Rearrange the relation so that M_2 stands alone on the left-hand side.

  3. Step 3 — List the givens: upstream Mach number (M_1) = 1.2500, specific heat ratio (k) = 1.3800.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    M2=0.8121M_{2} = 0.8121
  6. Step 6 — Check: returning M_2 = 0.8121 to

    M22=M12+2k−12kk−1M12−1M_2^2 = \dfrac{M_1^2 + \dfrac{2}{k-1}}{\dfrac{2k}{k-1}M_1^2 - 1}

    reproduces the given quantities, and both sides carry the same units.

Answer:
M2=0.8121M_{2} = 0.8121

Why the other options are there

  • 1.6243 — kept a factor of two that cancels in the correct rearrangement.
  • 0.4061 — dropped that same factor in the other direction.
  • 0.8934 — rounded an intermediate value before the final step.

Reference: FE Handbook — Normal Shock Relationships

Example 3
Normal shock relationships — solve for downstream Mach number (case 3) — Normal Shock Relationships (3)

normal shock relationships for flow in a supersonic nozzle Given upstream Mach number (M_1) = 1.2000; specific heat ratio (k) = 1.3500, determine the downstream Mach number (M_2).

Given

  • upstreamMachnumber(M1)=1.2000upstream Mach number (M_1) = 1.2000
  • specificheatratio(k)=1.3500specific heat ratio (k) = 1.3500

Find

downstream Mach number (M_2)

Start with the thinking

  • The governing relation printed in this handbook section is Normal shock relationships.
  • Everything except M_2 is given, so isolate M_2 symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Normal shock relationships give the downstream Mach number for supersonic flow crossing a normal shock.

Step-by-step solution

  1. Step 1 — State the governing relation:

    M22=M12+2k−12kk−1M12−1M_2^2 = \dfrac{M_1^2 + \dfrac{2}{k-1}}{\dfrac{2k}{k-1}M_1^2 - 1}
  2. Step 2 — Rearrange the relation so that M_2 stands alone on the left-hand side.

  3. Step 3 — List the givens: upstream Mach number (M_1) = 1.2000, specific heat ratio (k) = 1.3500.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    M2=0.8413M_{2} = 0.8413
  6. Step 6 — Check: returning M_2 = 0.8413 to

    M22=M12+2k−12kk−1M12−1M_2^2 = \dfrac{M_1^2 + \dfrac{2}{k-1}}{\dfrac{2k}{k-1}M_1^2 - 1}

    reproduces the given quantities, and both sides carry the same units.

Answer:
M2=0.8413M_{2} = 0.8413

Why the other options are there

  • 1.6826 — kept a factor of two that cancels in the correct rearrangement.
  • 0.4206 — dropped that same factor in the other direction.
  • 0.9254 — rounded an intermediate value before the final step.

Reference: FE Handbook — Normal Shock Relationships

Example 4
Normal shock relationships — solve for downstream Mach number (case 4) — Normal Shock Relationships (4)

normal shock relationships in a supersonic wind tunnel diffuser Given upstream Mach number (M_1) = 2.4500; specific heat ratio (k) = 1.3900, determine the downstream Mach number (M_2).

Given

  • upstreamMachnumber(M1)=2.4500upstream Mach number (M_1) = 2.4500
  • specificheatratio(k)=1.3900specific heat ratio (k) = 1.3900

Find

downstream Mach number (M_2)

Start with the thinking

  • The governing relation printed in this handbook section is Normal shock relationships.
  • Everything except M_2 is given, so isolate M_2 symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Normal shock relationships give the downstream Mach number for supersonic flow crossing a normal shock.

Step-by-step solution

  1. Step 1 — State the governing relation:

    M22=M12+2k−12kk−1M12−1M_2^2 = \dfrac{M_1^2 + \dfrac{2}{k-1}}{\dfrac{2k}{k-1}M_1^2 - 1}
  2. Step 2 — Rearrange the relation so that M_2 stands alone on the left-hand side.

  3. Step 3 — List the givens: upstream Mach number (M_1) = 2.4500, specific heat ratio (k) = 1.3900.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    M2=0.5161M_{2} = 0.5161
  6. Step 6 — Check: returning M_2 = 0.5161 to

    M22=M12+2k−12kk−1M12−1M_2^2 = \dfrac{M_1^2 + \dfrac{2}{k-1}}{\dfrac{2k}{k-1}M_1^2 - 1}

    reproduces the given quantities, and both sides carry the same units.

Answer:
M2=0.5161M_{2} = 0.5161

Why the other options are there

  • 1.0322 — kept a factor of two that cancels in the correct rearrangement.
  • 0.2581 — dropped that same factor in the other direction.
  • 0.5677 — rounded an intermediate value before the final step.

Reference: FE Handbook — Normal Shock Relationships

Example 5
Normal shock relationships — solve for downstream Mach number (case 5) — Normal Shock Relationships (5)

normal shock relationships ahead of a blunt body in supersonic flow Given upstream Mach number (M_1) = 1.7500; specific heat ratio (k) = 1.3500, determine the downstream Mach number (M_2).

Given

  • upstreamMachnumber(M1)=1.7500upstream Mach number (M_1) = 1.7500
  • specificheatratio(k)=1.3500specific heat ratio (k) = 1.3500

Find

downstream Mach number (M_2)

Start with the thinking

  • The governing relation printed in this handbook section is Normal shock relationships.
  • Everything except M_2 is given, so isolate M_2 symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Normal shock relationships give the downstream Mach number for supersonic flow crossing a normal shock.

Step-by-step solution

  1. Step 1 — State the governing relation:

    M22=M12+2k−12kk−1M12−1M_2^2 = \dfrac{M_1^2 + \dfrac{2}{k-1}}{\dfrac{2k}{k-1}M_1^2 - 1}
  2. Step 2 — Rearrange the relation so that M_2 stands alone on the left-hand side.

  3. Step 3 — List the givens: upstream Mach number (M_1) = 1.7500, specific heat ratio (k) = 1.3500.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    M2=0.6228M_{2} = 0.6228
  6. Step 6 — Check: returning M_2 = 0.6228 to

    M22=M12+2k−12kk−1M12−1M_2^2 = \dfrac{M_1^2 + \dfrac{2}{k-1}}{\dfrac{2k}{k-1}M_1^2 - 1}

    reproduces the given quantities, and both sides carry the same units.

Answer:
M2=0.6228M_{2} = 0.6228

Why the other options are there

  • 1.2457 — kept a factor of two that cancels in the correct rearrangement.
  • 0.3114 — dropped that same factor in the other direction.
  • 0.6851 — rounded an intermediate value before the final step.

Reference: FE Handbook — Normal Shock Relationships

Example 6
Normal shock relationships — solve for downstream Mach number (case 6) — Normal Shock Relationships (6)

normal shock relationships for flow in a supersonic nozzle Given upstream Mach number (M_1) = 1.3000; specific heat ratio (k) = 1.3600, determine the downstream Mach number (M_2).

Given

  • upstreamMachnumber(M1)=1.3000upstream Mach number (M_1) = 1.3000
  • specificheatratio(k)=1.3600specific heat ratio (k) = 1.3600

Find

downstream Mach number (M_2)

Start with the thinking

  • The governing relation printed in this handbook section is Normal shock relationships.
  • Everything except M_2 is given, so isolate M_2 symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Normal shock relationships give the downstream Mach number for supersonic flow crossing a normal shock.

Step-by-step solution

  1. Step 1 — State the governing relation:

    M22=M12+2k−12kk−1M12−1M_2^2 = \dfrac{M_1^2 + \dfrac{2}{k-1}}{\dfrac{2k}{k-1}M_1^2 - 1}
  2. Step 2 — Rearrange the relation so that M_2 stands alone on the left-hand side.

  3. Step 3 — List the givens: upstream Mach number (M_1) = 1.3000, specific heat ratio (k) = 1.3600.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    M2=0.7846M_{2} = 0.7846
  6. Step 6 — Check: returning M_2 = 0.7846 to

    M22=M12+2k−12kk−1M12−1M_2^2 = \dfrac{M_1^2 + \dfrac{2}{k-1}}{\dfrac{2k}{k-1}M_1^2 - 1}

    reproduces the given quantities, and both sides carry the same units.

Answer:
M2=0.7846M_{2} = 0.7846

Why the other options are there

  • 1.5693 — kept a factor of two that cancels in the correct rearrangement.
  • 0.3923 — dropped that same factor in the other direction.
  • 0.8631 — rounded an intermediate value before the final step.

Reference: FE Handbook — Normal Shock Relationships

Example 7
Normal shock relationships — solve for downstream Mach number (case 7) — Normal Shock Relationships (7)

normal shock relationships in a supersonic wind tunnel diffuser Given upstream Mach number (M_1) = 2.5500; specific heat ratio (k) = 1.3900, determine the downstream Mach number (M_2).

Given

  • upstreamMachnumber(M1)=2.5500upstream Mach number (M_1) = 2.5500
  • specificheatratio(k)=1.3900specific heat ratio (k) = 1.3900

Find

downstream Mach number (M_2)

Start with the thinking

  • The governing relation printed in this handbook section is Normal shock relationships.
  • Everything except M_2 is given, so isolate M_2 symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Normal shock relationships give the downstream Mach number for supersonic flow crossing a normal shock.

Step-by-step solution

  1. Step 1 — State the governing relation:

    M22=M12+2k−12kk−1M12−1M_2^2 = \dfrac{M_1^2 + \dfrac{2}{k-1}}{\dfrac{2k}{k-1}M_1^2 - 1}
  2. Step 2 — Rearrange the relation so that M_2 stands alone on the left-hand side.

  3. Step 3 — List the givens: upstream Mach number (M_1) = 2.5500, specific heat ratio (k) = 1.3900.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    M2=0.5064M_{2} = 0.5064
  6. Step 6 — Check: returning M_2 = 0.5064 to

    M22=M12+2k−12kk−1M12−1M_2^2 = \dfrac{M_1^2 + \dfrac{2}{k-1}}{\dfrac{2k}{k-1}M_1^2 - 1}

    reproduces the given quantities, and both sides carry the same units.

Answer:
M2=0.5064M_{2} = 0.5064

Why the other options are there

  • 1.0128 — kept a factor of two that cancels in the correct rearrangement.
  • 0.2532 — dropped that same factor in the other direction.
  • 0.5571 — rounded an intermediate value before the final step.

Reference: FE Handbook — Normal Shock Relationships

Example 8
Normal shock relationships — solve for downstream Mach number (case 8) — Normal Shock Relationships (8)

normal shock relationships ahead of a blunt body in supersonic flow Given upstream Mach number (M_1) = 1.4000; specific heat ratio (k) = 1.3900, determine the downstream Mach number (M_2).

Given

  • upstreamMachnumber(M1)=1.4000upstream Mach number (M_1) = 1.4000
  • specificheatratio(k)=1.3900specific heat ratio (k) = 1.3900

Find

downstream Mach number (M_2)

Start with the thinking

  • The governing relation printed in this handbook section is Normal shock relationships.
  • Everything except M_2 is given, so isolate M_2 symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Normal shock relationships give the downstream Mach number for supersonic flow crossing a normal shock.

Step-by-step solution

  1. Step 1 — State the governing relation:

    M22=M12+2k−12kk−1M12−1M_2^2 = \dfrac{M_1^2 + \dfrac{2}{k-1}}{\dfrac{2k}{k-1}M_1^2 - 1}
  2. Step 2 — Rearrange the relation so that M_2 stands alone on the left-hand side.

  3. Step 3 — List the givens: upstream Mach number (M_1) = 1.4000, specific heat ratio (k) = 1.3900.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    M2=0.7392M_{2} = 0.7392
  6. Step 6 — Check: returning M_2 = 0.7392 to

    M22=M12+2k−12kk−1M12−1M_2^2 = \dfrac{M_1^2 + \dfrac{2}{k-1}}{\dfrac{2k}{k-1}M_1^2 - 1}

    reproduces the given quantities, and both sides carry the same units.

Answer:
M2=0.7392M_{2} = 0.7392

Why the other options are there

  • 1.4785 — kept a factor of two that cancels in the correct rearrangement.
  • 0.3696 — dropped that same factor in the other direction.
  • 0.8131 — rounded an intermediate value before the final step.

Reference: FE Handbook — Normal Shock Relationships

Example 9
Normal shock relationships — solve for downstream Mach number (case 9) — Normal Shock Relationships (9)

normal shock relationships for flow in a supersonic nozzle Given upstream Mach number (M_1) = 2.9500; specific heat ratio (k) = 1.3400, determine the downstream Mach number (M_2).

Given

  • upstreamMachnumber(M1)=2.9500upstream Mach number (M_1) = 2.9500
  • specificheatratio(k)=1.3400specific heat ratio (k) = 1.3400

Find

downstream Mach number (M_2)

Start with the thinking

  • The governing relation printed in this handbook section is Normal shock relationships.
  • Everything except M_2 is given, so isolate M_2 symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Normal shock relationships give the downstream Mach number for supersonic flow crossing a normal shock.

Step-by-step solution

  1. Step 1 — State the governing relation:

    M22=M12+2k−12kk−1M12−1M_2^2 = \dfrac{M_1^2 + \dfrac{2}{k-1}}{\dfrac{2k}{k-1}M_1^2 - 1}
  2. Step 2 — Rearrange the relation so that M_2 stands alone on the left-hand side.

  3. Step 3 — List the givens: upstream Mach number (M_1) = 2.9500, specific heat ratio (k) = 1.3400.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    M2=0.4645M_{2} = 0.4645
  6. Step 6 — Check: returning M_2 = 0.4645 to

    M22=M12+2k−12kk−1M12−1M_2^2 = \dfrac{M_1^2 + \dfrac{2}{k-1}}{\dfrac{2k}{k-1}M_1^2 - 1}

    reproduces the given quantities, and both sides carry the same units.

Answer:
M2=0.4645M_{2} = 0.4645

Why the other options are there

  • 0.9290 — kept a factor of two that cancels in the correct rearrangement.
  • 0.2323 — dropped that same factor in the other direction.
  • 0.5110 — rounded an intermediate value before the final step.

Reference: FE Handbook — Normal Shock Relationships

Example 10
Normal shock relationships — solve for downstream Mach number (case 10) — Normal Shock Relationships (10)

normal shock relationships in a supersonic wind tunnel diffuser Given upstream Mach number (M_1) = 2.1500; specific heat ratio (k) = 1.3700, determine the downstream Mach number (M_2).

Given

  • upstreamMachnumber(M1)=2.1500upstream Mach number (M_1) = 2.1500
  • specificheatratio(k)=1.3700specific heat ratio (k) = 1.3700

Find

downstream Mach number (M_2)

Start with the thinking

  • The governing relation printed in this handbook section is Normal shock relationships.
  • Everything except M_2 is given, so isolate M_2 symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Normal shock relationships give the downstream Mach number for supersonic flow crossing a normal shock.

Step-by-step solution

  1. Step 1 — State the governing relation:

    M22=M12+2k−12kk−1M12−1M_2^2 = \dfrac{M_1^2 + \dfrac{2}{k-1}}{\dfrac{2k}{k-1}M_1^2 - 1}
  2. Step 2 — Rearrange the relation so that M_2 stands alone on the left-hand side.

  3. Step 3 — List the givens: upstream Mach number (M_1) = 2.1500, specific heat ratio (k) = 1.3700.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    M2=0.5493M_{2} = 0.5493
  6. Step 6 — Check: returning M_2 = 0.5493 to

    M22=M12+2k−12kk−1M12−1M_2^2 = \dfrac{M_1^2 + \dfrac{2}{k-1}}{\dfrac{2k}{k-1}M_1^2 - 1}

    reproduces the given quantities, and both sides carry the same units.

Answer:
M2=0.5493M_{2} = 0.5493

Why the other options are there

  • 1.0987 — kept a factor of two that cancels in the correct rearrangement.
  • 0.2747 — dropped that same factor in the other direction.
  • 0.6043 — rounded an intermediate value before the final step.

Reference: FE Handbook — Normal Shock Relationships

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